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ΓòÉΓòÉΓòÉ 1. -Preface- ΓòÉΓòÉΓòÉ
ADA REFERENCE MANUAL
Language and Standard Libraries
Version 6.0
21 December 1994
Copyright (C) 1992,1993,1994,1995 Intermetrics, Inc.
This copyright is assigned to the U.S. Government.
All rights reserved.
This document may be copied, in whole or in part, in any form or by any means,
as is or with alterations, provided that (1) alterations are clearly marked as
alterations and (2) this copyright notice is included unmodified in any copy.
Compiled copies of standard library units and examples need not contain this
copyright notice so long as the notice is included in all copies of source code
and documentation.
ADA REFERENCE MANUAL
Language and Standard Libraries
Version 6.0
Foreword Information about this standard
Introduction Introduction to the standard
1 General
2 Lexical Elements
3 Declarations and Types
4 Names and Expressions
5 Statements
6 Subprograms
7 Packages
8 Visibility Rules
9 Tasks and Synchronization
10 Program Structure and Compilation Issues
11 Exceptions
12 Generic Units
13 Representation Issues ANNEXES
A Predefined Language Environment
B Interface to Other Languages
C Systems Programming
D Real-Time Systems
E Distributed Systems
F Information Systems
G Numerics
H Safety and Security
J Obsolescent Features
K Language-Defined Attributes
L Language-Defined Pragmas
M Implementation-Defined Characteristics
N Glossary
P Syntax Summary
Index --- The Detailed Node Listing ---
Foreword Foreword
Introduction Introduction
Design Goals Design Goals
Language Summary Language Summary
Program Units Program Units
Declarations and Statements Declarations and Statements
Data Types Data Types
Other Facilities Other Facilities
Language Changes Language Changes
Instructions for Comment SubmissionInstructions for Comment Submission
Acknowledgements Acknowledgements
1 General
1.1 Scope
1.1.1 Extent
1.1.2 Structure
1.1.3 Conformity of an Implementation with the
Standard
1.1.4 Method of Description and Syntax Notation
1.1.5 Classification of Errors
1.2 Normative References
1.3 Definitions
2 Lexical Elements
2.1 Character Set
2.2 Lexical Elements, Separators, and Delimiters
2.3 Identifiers
2.4 Numeric Literals
2.4.1 Decimal Literals
2.4.2 Based Literals
2.5 Character Literals
2.6 String Literals
2.7 Comments
2.8 Pragmas
2.9 Reserved Words
3 Declarations and Types
3.1 Declarations
3.2 Types and Subtypes
3.2.1 Type Declarations
3.2.2 Subtype Declarations
3.2.3 Classification of Operations
3.3 Objects and Named Numbers
3.3.1 Object Declarations
3.3.2 Number Declarations
3.4 Derived Types and Classes
3.4.1 Derivation Classes
3.5 Scalar Types
3.5.1 Enumeration Types
3.5.2 Character Types
3.5.3 Boolean Types
3.5.4 Integer Types
3.5.5 Operations of Discrete Types
3.5.6 Real Types
3.5.7 Floating Point Types
3.5.8 Operations of Floating Point Types
3.5.9 Fixed Point Types
3.5.10 Operations of Fixed Point Types
3.6 Array Types
3.6.1 Index Constraints and Discrete Ranges
3.6.2 Operations of Array Types
3.6.3 String Types
3.7 Discriminants
3.7.1 Discriminant Constraints
3.7.2 Operations of Discriminated Types
3.8 Record Types
3.8.1 Variant Parts and Discrete Choices
3.9 Tagged Types and Type Extensions
3.9.1 Type Extensions
3.9.2 Dispatching Operations of Tagged Types
3.9.3 Abstract Types and Subprograms
3.10 Access Types
3.10.1 Incomplete Type Declarations
3.10.2 Operations of Access Types
3.11 Declarative Parts
3.11.1 Completions of Declarations
4 Names and Expressions
4.1 Names
4.1.1 Indexed Components
4.1.2 Slices
4.1.3 Selected Components
4.1.4 Attributes
4.2 Literals
4.3 Aggregates
4.3.1 Record Aggregates
4.3.2 Extension Aggregates
4.3.3 Array Aggregates
4.4 Expressions
4.5 Operators and Expression Evaluation
4.5.1 Logical Operators and Short-circuit Control
Forms
4.5.2 Relational Operators and Membership Tests
4.5.3 Binary Adding Operators
4.5.4 Unary Adding Operators
4.5.5 Multiplying Operators
4.5.6 Highest Precedence Operators
4.6 Type Conversions
4.7 Qualified Expressions
4.8 Allocators
4.9 Static Expressions and Static Subtypes
4.9.1 Statically Matching Constraints and Subtypes
5 Statements
5.1 Simple and Compound Statements - Sequences of
Statements
5.2 Assignment Statements
5.3 If Statements
5.4 Case Statements
5.5 Loop Statements
5.6 Block Statements
5.7 Exit Statements
5.8 Goto Statements
6 Subprograms
6.1 Subprogram Declarations
6.2 Formal Parameter Modes
6.3 Subprogram Bodies
6.3.1 Conformance Rules
6.3.2 Inline Expansion of Subprograms
6.4 Subprogram Calls
6.4.1 Parameter Associations
6.5 Return Statements
6.6 Overloading of Operators
7 Packages
7.1 Package Specifications and Declarations
7.2 Package Bodies
7.3 Private Types and Private Extensions
7.3.1 Private Operations
7.4 Deferred Constants
7.5 Limited Types
7.6 User-Defined Assignment and Finalization
7.6.1 Completion and Finalization
8 Visibility Rules
8.1 Declarative Region
8.2 Scope of Declarations
8.3 Visibility
8.4 Use Clauses
8.5 Renaming Declarations
8.5.1 Object Renaming Declarations
8.5.2 Exception Renaming Declarations
8.5.3 Package Renaming Declarations
8.5.4 Subprogram Renaming Declarations
8.5.5 Generic Renaming Declarations
8.6 The Context of Overload Resolution
9 Tasks and Synchronization
9.1 Task Units and Task Objects
9.2 Task Execution - Task Activation
9.3 Task Dependence - Termination of Tasks
9.4 Protected Units and Protected Objects
9.5 Intertask Communication
9.5.1 Protected Subprograms and Protected Actions
9.5.2 Entries and Accept Statements
9.5.3 Entry Calls
9.5.4 Requeue Statements
9.6 Delay Statements, Duration, and Time
9.7 Select Statements
9.7.1 Selective Accept
9.7.2 Timed Entry Calls
9.7.3 Conditional Entry Calls
9.7.4 Asynchronous Transfer of Control
9.8 Abort of a Task - Abort of a Sequence of
Statements
9.9 Task and Entry Attributes
9.10 Shared Variables
9.11 Example of Tasking and Synchronization
10 Program Structure and Compilation Issues
10.1 Separate Compilation
10.1.1 Compilation Units - Library Units
10.1.2 Context Clauses - With Clauses
10.1.3 Subunits of Compilation Units
10.1.4 The Compilation Process
10.1.5 Pragmas and Program Units
10.1.6 Environment-Level Visibility Rules
10.2 Program Execution
10.2.1 Elaboration Control
11 Exceptions
11.1 Exception Declarations
11.2 Exception Handlers
11.3 Raise Statements
11.4 Exception Handling
11.4.1 The Package Exceptions
11.4.2 Example of Exception Handling
11.5 Suppressing Checks
11.6 Exceptions and Optimization
12 Generic Units
12.1 Generic Declarations
12.2 Generic Bodies
12.3 Generic Instantiation
12.4 Formal Objects
12.5 Formal Types
12.5.1 Formal Private and Derived Types
12.5.2 Formal Scalar Types
12.5.3 Formal Array Types
12.5.4 Formal Access Types
12.6 Formal Subprograms
12.7 Formal Packages
12.8 Example of a Generic Package
13 Representation Issues
13.1 Representation Items
13.2 Pragma Pack
13.3 Representation Attributes
13.4 Enumeration Representation Clauses
13.5 Record Layout
13.5.1 Record Representation Clauses
13.5.2 Storage Place Attributes
13.5.3 Bit Ordering
13.6 Change of Representation
13.7 The Package System
13.7.1 The Package System.Storage_Elements
13.7.2 The Package System.Address_To_Access_Conversions
13.8 Machine Code Insertions
13.9 Unchecked Type Conversions
13.9.1 Data Validity
13.9.2 The Valid Attribute
13.10 Unchecked Access Value Creation
13.11 Storage Management
13.11.1 The Max_Size_In_Storage_Elements Attribute
13.11.2 Unchecked Storage Deallocation
13.11.3 Pragma Controlled
13.12 Pragma Restrictions
13.13 Streams
13.13.1 The Package Streams
13.13.2 Stream-Oriented Attributes
13.14 Freezing Rules ANNEXES
A Predefined Language Environment
A.1 The Package Standard
A.2 The Package Ada
A.3 Character Handling
A.3.1 The Package Characters
A.3.2 The Package Characters.Handling
A.3.3 The Package Characters.Latin_1
A.4 String Handling
A.4.1 The Package Strings
A.4.2 The Package Strings.Maps
A.4.3 Fixed-Length String Handling
A.4.4 Bounded-Length String Handling
A.4.5 Unbounded-Length String Handling
A.4.6 String-Handling Sets and Mappings
A.4.7 Wide_String Handling
A.5 The Numerics Packages
A.5.1 Elementary Functions
A.5.2 Random Number Generation
A.5.3 Attributes of Floating Point Types
A.5.4 Attributes of Fixed Point Types
A.6 Input-Output
A.7 External Files and File Objects
A.8 Sequential and Direct Files
A.8.1 The Generic Package Sequential_IO
A.8.2 File Management
A.8.3 Sequential Input-Output Operations
A.8.4 The Generic Package Direct_IO
A.8.5 Direct Input-Output Operations
A.9 The Generic Package Storage_IO
A.10 Text Input-Output
A.10.1 The Package Text_IO
A.10.2 Text File Management
A.10.3 Default Input, Output, and Error Files
A.10.4 Specification of Line and Page Lengths
A.10.5 Operations on Columns, Lines, and Pages
A.10.6 Get and Put Procedures
A.10.7 Input-Output of Characters and Strings
A.10.8 Input-Output for Integer Types
A.10.9 Input-Output for Real Types
A.10.10 Input-Output for Enumeration Types
A.11 Wide Text Input-Output
A.12 Stream Input-Output
A.12.1 The Package Streams.Stream_IO
A.12.2 The Package Text_IO.Text_Streams
A.12.3 The Package Wide_Text_IO.Text_Streams
A.13 Exceptions in Input-Output
A.14 File Sharing
A.15 The Package Command_Line
B Interface to Other Languages
B.1 Interfacing Pragmas
B.2 The Package Interfaces
B.3 Interfacing with C
B.3.1 The Package Interfaces.C.Strings
B.3.2 The Generic Package Interfaces.C.Pointers
B.4 Interfacing with COBOL
B.5 Interfacing with Fortran
C Systems Programming
C.1 Access to Machine Operations
C.2 Required Representation Support
C.3 Interrupt Support
C.3.1 Protected Procedure Handlers
C.3.2 The Package Interrupts
C.4 Preelaboration Requirements
C.5 Pragma Discard_Names
C.6 Shared Variable Control
C.7 Task Identification and Attributes
C.7.1 The Package Task_Identification
C.7.2 The Package Task_Attributes
D Real-Time Systems
D.1 Task Priorities
D.2 Priority Scheduling
D.2.1 The Task Dispatching Model
D.2.2 The Standard Task Dispatching Policy
D.3 Priority Ceiling Locking
D.4 Entry Queuing Policies
D.5 Dynamic Priorities
D.6 Preemptive Abort
D.7 Tasking Restrictions
D.8 Monotonic Time
D.9 Delay Accuracy
D.10 Synchronous Task Control
D.11 Asynchronous Task Control
D.12 Other Optimizations and Determinism Rules
E Distributed Systems
E.1 Partitions
E.2 Categorization of Library Units
E.2.1 Shared Passive Library Units
E.2.2 Remote Types Library Units
E.2.3 Remote Call Interface Library Units
E.3 Consistency of a Distributed System
E.4 Remote Subprogram Calls
E.4.1 Pragma Asynchronous
E.4.2 Example of Use of a Remote Access-to-Class-Wide
Type
E.5 Partition Communication Subsystem
F Information Systems
F.1 Machine_Radix Attribute Definition Clause
F.2 The Package Decimal
F.3 Edited Output for Decimal Types
F.3.1 Picture String Formation
F.3.2 Edited Output Generation
F.3.3 The Package Text_IO.Editing
F.3.4 The Package Wide_Text_IO.Editing
G Numerics
G.1 Complex Arithmetic
G.1.1 Complex Types
G.1.2 Complex Elementary Functions
G.1.3 Complex Input-Output
G.1.4 The Package Wide_Text_IO.Complex_IO
G.2 Numeric Performance Requirements
G.2.1 Model of Floating Point Arithmetic
G.2.2 Model-Oriented Attributes of Floating Point
Types
G.2.3 Model of Fixed Point Arithmetic
G.2.4 Accuracy Requirements for the Elementary
Functions
G.2.5 Performance Requirements for Random Number
Generation
G.2.6 Accuracy Requirements for Complex Arithmetic
H Safety and Security
H.1 Pragma Normalize_Scalars
H.2 Documentation of Implementation Decisions
H.3 Reviewable Object Code
H.3.1 Pragma Reviewable
H.3.2 Pragma Inspection_Point
H.4 Safety and Security Restrictions
J Obsolescent Features
J.1 Renamings of Ada 83 Library Units
J.2 Allowed Replacements of Characters
J.3 Reduced Accuracy Subtypes
J.4 The Constrained Attribute
J.5 ASCII
J.6 Numeric_Error
J.7 At Clauses
J.7.1 Interrupt Entries
J.8 Mod Clauses
J.9 The Storage_Size Attribute
K Language-Defined Attributes
L Language-Defined Pragmas
M Implementation-Defined Characteristics
N Glossary
P Syntax Summary
Index Index
Index.Operators Index.Operators
Index.Digits Index.Digits
Index.A Index.A
Index.B Index.B
Index.C Index.C
Index.D Index.D
Index.E Index.E
Index.F Index.F
Index.G Index.G
Index.H Index.H
Index.I Index.I
Index.J Index.J
Index.K Index.K
Index.L Index.L
Index.M Index.M
Index.N Index.N
Index.O Index.O
Index.P Index.P
Index.Q Index.Q
Index.R Index.R
Index.S Index.S
Index.T Index.T
Index.U Index.U
Index.V Index.V
Index.W Index.W
Index.X Index.X
Index.Y Index.Y
ΓòÉΓòÉΓòÉ 2. Foreword ΓòÉΓòÉΓòÉ
1. ISO (the International Organization for Standardization) and IEC (the
International Electrotechnical Commission) form the specialized system
for worldwide standardization. National bodies that are members of ISO or
IEC participate in the development of International Standards through
technical committees established by the respective organization to deal
with particular fields of technical activity. ISO and IEC technical
committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and
IEC, also take part in the work.
2. In the field of information technology, ISO and IEC have established a
joint technical committee, ISO/IEC JTC 1. Draft International Standards
adopted by the joint technical committee are circulated to national
bodies for voting. Publication as an International Standard requires
approval by at least 75 % of the national bodies casting a vote.
3. International Standard ISO/IEC 8652 was prepared by Joint Technical
Committee ISO/IEC JTC 1, Information Technology.
4. This second edition cancels and replaces the first edition (ISO
8652:1987), of which it constitutes a technical revision.
5. Annexes A to J form an integral part of this International Standard.
Annexes K to P are for information only.
ΓòÉΓòÉΓòÉ 3. Introduction ΓòÉΓòÉΓòÉ
1. This is the Ada Reference Manual.
2. Other available Ada documents include:
a. Rationale for the Ada Programming Language -- 1995 edition, which
gives an introduction to the new features of Ada, and explains the
rationale behind them. Programmers should read this first.
b. Changes to Ada -- 1987 to 1995. This document lists in detail the
changes made to the 1987 edition of the standard.
c. The Annotated Ada Reference Manual (AARM). The AARM contains all of
the text in the RM95, plus various annotations. It is intended
primarily for compiler writers, validation test writers, and others
who wish to study the fine details. The annotations include detailed
rationale for individual rules and explanations of some of the more
arcane interactions among the rules.
Design Goals Design Goals
Language Summary Language Summary
Program Units Program Units
Declarations and Statements Declarations and Statements
Data Types Data Types
Other Facilities Other Facilities
Language Changes Language Changes
Instructions for Comment SubmissionInstructions for Comment Submission
Acknowledgements Acknowledgements
ΓòÉΓòÉΓòÉ 3.1. Design Goals ΓòÉΓòÉΓòÉ
1. Ada was originally designed with three overriding concerns: program
reliability and maintenance, programming as a human activity, and
efficiency. This revision to the language was designed to provide greater
flexibility and extensibility, additional control over storage management
and synchronization, and standardized packages oriented toward supporting
important application areas, while at the same time retaining the
original emphasis on reliability, maintainability, and efficiency.
2. The need for languages that promote reliability and simplify maintenance
is well established. Hence emphasis was placed on program readability
over ease of writing. For example, the rules of the language require that
program variables be explicitly declared and that their type be
specified. Since the type of a variable is invariant, compilers can
ensure that operations on variables are compatible with the properties
intended for objects of the type. Furthermore, error-prone notations have
been avoided, and the syntax of the language avoids the use of encoded
forms in favor of more English-like constructs. Finally, the language
offers support for separate compilation of program units in a way that
facilitates program development and maintenance, and which provides the
same degree of checking between units as within a unit.
3. Concern for the human programmer was also stressed during the design.
Above all, an attempt was made to keep to a relatively small number of
underlying concepts integrated in a consistent and systematic way while
continuing to avoid the pitfalls of excessive involution. The design
especially aims to provide language constructs that correspond
intuitively to the normal expectations of users.
4. Like many other human activities, the development of programs is becoming
ever more decentralized and distributed. Consequently, the ability to
assemble a program from independently produced software components
continues to be a central idea in the design. The concepts of packages,
of private types, and of generic units are directly related to this idea,
which has ramifications in many other aspects of the language. An allied
concern is the maintenance of programs to match changing requirements;
type extension and the hierarchical library enable a program to be
modified while minimizing disturbance to existing tested and trusted
components.
5. No language can avoid the problem of efficiency. Languages that require
over-elaborate compilers, or that lead to the inefficient use of storage
or execution time, force these inefficiencies on all machines and on all
programs. Every construct of the language was examined in the light of
present implementation techniques. Any proposed construct whose
implementation was unclear or that required excessive machine resources
was rejected.
ΓòÉΓòÉΓòÉ 3.2. Language Summary ΓòÉΓòÉΓòÉ
1. An Ada program is composed of one or more program units. Program units
may be subprograms (which define executable algorithms), packages (which
define collections of entities), task units (which define concurrent
computations), protected units (which define operations for the
coordinated sharing of data between tasks), or generic units (which
define parameterized forms of packages and subprograms). Each program
unit normally consists of two parts: a specification, containing the
information that must be visible to other units, and a body, containing
the implementation details, which need not be visible to other units.
Most program units can be compiled separately.
2. This distinction of the specification and body, and the ability to
compile units separately, allows a program to be designed, written, and
tested as a set of largely independent software components.
3. An Ada program will normally make use of a library of program units of
general utility. The language provides means whereby individual
organizations can construct their own libraries. All libraries are
structured in a hierarchical manner; this enables the logical
decomposition of a subsystem into individual components. The text of a
separately compiled program unit must name the library units it requires.
ΓòÉΓòÉΓòÉ 3.3. Program Units ΓòÉΓòÉΓòÉ
1. A subprogram is the basic unit for expressing an algorithm. There are two
kinds of subprograms: procedures and functions. A procedure is the means
of invoking a series of actions. For example, it may read data, update
variables, or produce some output. It may have parameters, to provide a
controlled means of passing information between the procedure and the
point of call. A function is the means of invoking the computation of a
value. It is similar to a procedure, but in addition will return a
result.
2. A package is the basic unit for defining a collection of logically
related entities. For example, a package can be used to define a set of
type declarations and associated operations. Portions of a package can be
hidden from the user, thus allowing access only to the logical properties
expressed by the package specification.
3. Subprogram and package units may be compiled separately and arranged in
hierarchies of parent and child units giving fine control over visibility
of the logical properties and their detailed implementation.
4. A task unit is the basic unit for defining a task whose sequence of
actions may be executed concurrently with those of other tasks. Such
tasks may be implemented on multicomputers, multiprocessors, or with
interleaved execution on a single processor. A task unit may define
either a single executing task or a task type permitting the creation of
any number of similar tasks.
5. A protected unit is the basic unit for defining protected operations for
the coordinated use of data shared between tasks. Simple mutual exclusion
is provided automatically, and more elaborate sharing protocols can be
defined. A protected operation can either be a subprogram or an entry. A
protected entry specifies a Boolean expression (an entry barrier) that
must be true before the body of the entry is executed. A protected unit
may define a single protected object or a protected type permitting the
creation of several similar objects.
ΓòÉΓòÉΓòÉ 3.4. Declarations and Statements ΓòÉΓòÉΓòÉ
1. The body of a program unit generally contains two parts: a declarative
part, which defines the logical entities to be used in the program unit,
and a sequence of statements, which defines the execution of the program
unit.
2. The declarative part associates names with declared entities. For
example, a name may denote a type, a constant, a variable, or an
exception. A declarative part also introduces the names and parameters of
other nested subprograms, packages, task units, protected units, and
generic units to be used in the program unit.
3. The sequence of statements describes a sequence of actions that are to be
performed. The statements are executed in succession (unless a transfer
of control causes execution to continue from another place).
4. An assignment statement changes the value of a variable. A procedure call
invokes execution of a procedure after associating any actual parameters
provided at the call with the corresponding formal parameters.
5. Case statements and if statements allow the selection of an enclosed
sequence of statements based on the value of an expression or on the
value of a condition.
6. The loop statement provides the basic iterative mechanism in the
language. A loop statement specifies that a sequence of statements is to
be executed repeatedly as directed by an iteration scheme, or until an
exit statement is encountered.
7. A block statement comprises a sequence of statements preceded by the
declaration of local entities used by the statements.
8. Certain statements are associated with concurrent execution. A delay
statement delays the execution of a task for a specified duration or
until a specified time. An entry call statement is written as a procedure
call statement; it requests an operation on a task or on a protected
object, blocking the caller until the operation can be performed. A
called task may accept an entry call by executing a corresponding accept
statement, which specifies the actions then to be performed as part of
the rendezvous with the calling task. An entry call on a protected object
is processed when the corresponding entry barrier evaluates to true,
whereupon the body of the entry is executed. The requeue statement
permits the provision of a service as a number of related activities with
preference control. One form of the select statement allows a selective
wait for one of several alternative rendezvous. Other forms of the select
statement allow conditional or timed entry calls and the asynchronous
transfer of control in response to some triggering event.
9. Execution of a program unit may encounter error situations in which
normal program execution cannot continue. For example, an arithmetic
computation may exceed the maximum allowed value of a number, or an
attempt may be made to access an array component by using an incorrect
index value. To deal with such error situations, the statements of a
program unit can be textually followed by exception handlers that specify
the actions to be taken when the error situation arises. Exceptions can
be raised explicitly by a raise statement.
ΓòÉΓòÉΓòÉ 3.5. Data Types ΓòÉΓòÉΓòÉ
1. Every object in the language has a type, which characterizes a set of
values and a set of applicable operations. The main classes of types are
elementary types (comprising enumeration, numeric, and access types) and
composite types (including array and record types).
2. An enumeration type defines an ordered set of distinct enumeration
literals, for example a list of states or an alphabet of characters. The
enumeration types Boolean, Character, and Wide_Character are predefined.
3. Numeric types provide a means of performing exact or approximate
numerical computations. Exact computations use integer types, which
denote sets of consecutive integers. Approximate computations use either
fixed point types, with absolute bounds on the error, or floating point
types, with relative bounds on the error. The numeric types Integer,
Float, and Duration are predefined.
4. Composite types allow definitions of structured objects with related
components. The composite types in the language include arrays and
records. An array is an object with indexed components of the same type.
A record is an object with named components of possibly different types.
Task and protected types are also forms of composite types. The array
types String and Wide_String are predefined.
5. Record, task, and protected types may have special components called
discriminants which parameterize the type. Variant record structures that
depend on the values of discriminants can be defined within a record
type.
6. Access types allow the construction of linked data structures. A value of
an access type represents a reference to an object declared as aliased or
to an object created by the evaluation of an allocator. Several variables
of an access type may designate the same object, and components of one
object may designate the same or other objects. Both the elements in such
linked data structures and their relation to other elements can be
altered during program execution. Access types also permit references to
subprograms to be stored, passed as parameters, and ultimately
dereferenced as part of an indirect call.
7. Private types permit restricted views of a type. A private type can be
defined in a package so that only the logically necessary properties are
made visible to the users of the type. The full structural details that
are externally irrelevant are then only available within the package and
any child units.
8. From any type a new type may be defined by derivation. A type, together
with its derivatives (both direct and indirect) form a derivation class.
Class-wide operations may be defined that accept as a parameter an
operand of any type in a derivation class. For record and private types,
the derivatives may be extensions of the parent type. Types that support
these object-oriented capabilities of class-wide operations and type
extension must be tagged, so that the specific type of an operand within
a derivation class can be identified at run time. When an operation of a
tagged type is applied to an operand whose specific type is not known
until run time, implicit dispatching is performed based on the tag of the
operand.
9. The concept of a type is further refined by the concept of a subtype,
whereby a user can constrain the set of allowed values of a type.
Subtypes can be used to define subranges of scalar types, arrays with a
limited set of index values, and records and private types with
particular discriminant values.
ΓòÉΓòÉΓòÉ 3.6. Other Facilities ΓòÉΓòÉΓòÉ
1. Representation clauses can be used to specify the mapping between types
and features of an underlying machine. For example, the user can specify
that objects of a given type must be represented with a given number of
bits, or that the components of a record are to be represented using a
given storage layout. Other features allow the controlled use of low
level, nonportable, or implementation-dependent aspects, including the
direct insertion of machine code.
2. The predefined environment of the language provides for input-output and
other capabilities (such as string manipulation and random number
generation) by means of standard library packages. Input-output is
supported for values of user-defined as well as of predefined types.
Standard means of representing values in display form are also provided.
Other standard library packages are defined in annexes of the standard to
support systems with specialized requirements.
3. Finally, the language provides a powerful means of parameterization of
program units, called generic program units. The generic parameters can
be types and subprograms (as well as objects and packages) and so allow
general algorithms and data structures to be defined that are applicable
to all types of a given class.
ΓòÉΓòÉΓòÉ 3.7. Language Changes ΓòÉΓòÉΓòÉ
1. This International Standard replaces the first edition of 1987. In this
edition, the following major language changes have been incorporated:
a. Support for standard 8-bit and 16-bit character sets. See 2, 3.5.2,
3.6.3, A.1, A.3, and A.4.
b. Object-oriented programming with run-time polymorphism. See the
discussions of classes, derived types, tagged types, record
extensions, and private extensions in clauses 3.4, 3.9, and 7.3.
See also the new forms of generic formal parameters that are allowed
by 12.5.1: ``Formal Private and Derived Types'', and 12.7: ``Formal
Packages''.
c. Access types have been extended to allow an access value to
designate a subprogram or an object declared by an object
declaration (as opposed to just a heap-allocated object) (see 3.10).
d. Efficient data-oriented synchronization is provided via protected
types. See 9.
e. The library units of a library may be organized into a hierarchy of
parent and child units (see 10).
f. Additional support has been added for interfacing to other
languages. See B.
g. The Specialized Needs Annexes have been added to provide specific
support for certain application areas:
1. Annex C, ``Systems Programming''
2. Annex D, ``Real-Time Systems''
3. Annex E, ``Distributed Systems''
4. Annex F, ``Information Systems''
5. Annex G, ``Numerics''
6. Annex H, ``Safety and Security''
ΓòÉΓòÉΓòÉ 3.8. Instructions for Comment Submission ΓòÉΓòÉΓòÉ
1. Informal comments on this International Standard may be sent via e-mail
to ada-comment@sw-eng.falls-church.va.us. If appropriate, the Project
Editor will initiate the defect correction procedure.
2. Comments should use the following format:
3.
!topic Title summarizing comment
!reference RM95-ss.ss(pp)
!from Author Name yy-mm-dd
!keywords keywords related to topic
!discussion
text of discussion
4. where ss.ss is the section, clause or subclause number, pp is the
paragraph number where applicable, and yy-mm-dd is the date the comment
was sent. The date is optional, as is the !keywords line.
5. Multiple comments per e-mail message are acceptable. Please use a
descriptive ``Subject'' in your e-mail message.
6. When correcting typographical errors or making minor wording suggestions,
please put the correction directly as the topic of the comment; use
square brackets [ ] to indicate text to be omitted and curly braces { }
to indicate text to be added, and provide enough context to make the
nature of the suggestion self-evident or put additional information in
the body of the comment, for example:
7.
!topic [c]{C}haracter
!topic it[']s meaning is not defined
8. Formal requests for interpretations and for reporting defects in this
International Standard may be made in accordance with the ISO/IEC JTC1
Directives and the ISO/IEC JTC1/SC22 policy for interpretations. National
Bodies may submit a Defect Report to ISO/IEC JTC1/SC22 for resolution
under the JTC1 procedures. A response will be provided and, if
appropriate, a Technical Corrigendum will be issued in accordance with
the procedures.
ΓòÉΓòÉΓòÉ 3.9. Acknowledgements ΓòÉΓòÉΓòÉ
1. This International Standard was prepared by the Ada 9X Mapping/Revision
Team based at Intermetrics, Inc., which has included: W. Carlson, Program
Manager; T. Taft, Technical Director; J. Barnes (consultant); B. Brosgol
(consultant); R. Duff (Oak Tree Software); M. Edwards; C. Garrity; R.
Hilliard; O. Pazy (consultant); D. Rosenfeld; L. Shafer; W. White; M.
Woodger.
2. The following consultants to the Ada 9X Project contributed to the
Specialized Needs Annexes: T. Baker (Real-Time/Systems Programming --
SEI, FSU); K. Dritz (Numerics -- Argonne National Laboratory); A. Gargaro
(Distributed Systems -- Computer Sciences); J. Goodenough
(Real-Time/Systems Programming -- SEI); J. McHugh (Secure Systems --
consultant); B. Wichmann (Safety-Critical Systems -- NPL: UK).
3. This work was regularly reviewed by the Ada 9X Distinguished Reviewers
and the members of the Ada 9X Rapporteur Group (XRG): E. Ploedereder,
Chairman of DRs and XRG (University of Stuttgart: Germany); B. Bardin
(Hughes); J. Barnes (consultant: UK); B. Brett (DEC); B. Brosgol
(consultant); R. Brukardt (RR Software); N. Cohen (IBM); R. Dewar (NYU);
G. Dismukes (TeleSoft); A. Evans (consultant); A. Gargaro (Computer
Sciences); M. Gerhardt (ESL); J. Goodenough (SEI); S. Heilbrunner
(University of Salzburg: Austria); P. Hilfinger (UC/Berkeley); B.
Kaellberg (CelsiusTech: Sweden); M. Kamrad II (Unisys); J. van Katwijk
(Delft University of Technology: The Netherlands); V. Kaufman (Russia);
P. Kruchten (Rational); R. Landwehr (CCI: Germany); C. Lester (Portsmouth
Polytechnic: UK); L. Mansson (TELIA Research: Sweden); S. Michell
(Multiprocessor Toolsmiths: Canada); M. Mills (US Air Force); D. Pogge
(US Navy); K. Power (Boeing); O. Roubine (Verdix: France); A. Strohmeier
(Swiss Fed Inst of Technology: Switzerland); W. Taylor (consultant: UK);
J. Tokar (Tartan); E. Vasilescu (Grumman); J. Vladik (Prospeks s.r.o.:
Czech Republic); S. Van Vlierberghe (OFFIS: Belgium).
4. Other valuable feedback influencing the revision process was provided by
the Ada 9X Language Precision Team (Odyssey Research Associates), the Ada
9X User/Implementer Teams (AETECH, Tartan, TeleSoft), the Ada 9X
Implementation Analysis Team (New York University) and the Ada
community-at-large.
5. Special thanks go to R. Mathis, Convenor of ISO/IEC JTC1/SC22 Working
Group 9.
6. The Ada 9X Project was sponsored by the Ada Joint Program Office.
Christine M. Anderson at the Air Force Phillips Laboratory (Kirtland AFB,
NM) was the project manager. Changes
7. The International Standard is the same as this version of the Reference
Manual, except:
a. This list of Changes is not included in the International Standard.
b. The ``Acknowledgements'' page is not included in the International
Standard.
c. The text in the running headers and footers on each page is slightly
different in the International Standard.
d. The title page(s) are different in the International Standard.
e. This document is formatted for 8.5-by-11-inch paper, whereas the
International Standard is formatted for A4 paper (210-by-297mm);
thus, the page breaks are in different places.
ΓòÉΓòÉΓòÉ 4. General ΓòÉΓòÉΓòÉ
1. Ada is a programming language designed to support the construction of
long-lived, highly reliable software systems. The language includes
facilities to define packages of related types, objects, and operations.
The packages may be parameterized and the types may be extended to
support the construction of libraries of reusable, adaptable software
components. The operations may be implemented as subprograms using
conventional sequential control structures, or as entries that include
synchronization of concurrent threads of control as part of their
invocation. The language treats modularity in the physical sense as well,
with a facility to support separate compilation.
2. The language includes a complete facility for the support of real-time,
concurrent programming. Errors can be signaled as exceptions and handled
explicitly. The language also covers systems programming; this requires
precise control over the representation of data and access to
system-dependent properties. Finally, a predefined environment of
standard packages is provided, including facilities for, among others,
input-output, string manipulation, numeric elementary functions, and
random number generation.
1.1 Scope
1.2 Normative References
1.3 Definitions --- The Detailed Node Listing ---
1 General
1.1 Scope
1.1.1 Extent
1.1.2 Structure
1.1.3 Conformity of an Implementation with the
Standard
1.1.4 Method of Description and Syntax Notation
1.1.5 Classification of Errors
1.2 Normative References
1.3 Definitions
ΓòÉΓòÉΓòÉ 4.1. Scope ΓòÉΓòÉΓòÉ
1. This International Standard specifies the form and meaning of programs
written in Ada. Its purpose is to promote the portability of Ada programs
to a variety of data processing systems.
1.1.1 Extent
1.1.2 Structure
1.1.3 Conformity of an Implementation with the
Standard
1.1.4 Method of Description and Syntax Notation
1.1.5 Classification of Errors
ΓòÉΓòÉΓòÉ 4.1.1. Extent ΓòÉΓòÉΓòÉ
1. This International Standard specifies:
a. The form of a program written in Ada;
b. The effect of translating and executing such a program;
c. The manner in which program units may be combined to form Ada
programs;
d. The language-defined library units that a conforming implementation
is required to supply;
e. The permissible variations within the standard, and the manner in
which they are to be documented;
f. Those violations of the standard that a conforming implementation is
required to detect, and the effect of attempting to translate or
execute a program containing such violations;
g. Those violations of the standard that a conforming implementation is
not required to detect.
1. This International Standard does not specify:
a. The means whereby a program written in Ada is transformed into
object code executable by a processor;
b. The means whereby translation or execution of programs is invoked
and the executing units are controlled;
c. The size or speed of the object code, or the relative execution
speed of different language constructs;
The form or contents of any listings produced by implementations; in
particular, the form or contents of error or warning messages;
d. The effect of unspecified execution.
e. The size of a program or program unit that will exceed the capacity
of a particular conforming implementation.
ΓòÉΓòÉΓòÉ 4.1.2. Structure ΓòÉΓòÉΓòÉ
1. This International Standard contains thirteen sections, fourteen annexes,
and an index.
2. The core of the Ada language consists of:
a. Sections 1 through 13
b. Annex A, ``Predefined Language Environment''
c. Annex B, ``Interface to Other Languages''
d. Annex J, ``Obsolescent Features''
1. The following Specialized Needs Annexes define features that are needed
by certain application areas:
a. Annex C, ``Systems Programming''
b. Annex D, ``Real-Time Systems''
c. Annex E, ``Distributed Systems''
d. Annex F, ``Information Systems''
e. Annex G, ``Numerics''
f. Annex H, ``Safety and Security''
1. The core language and the Specialized Needs Annexes are normative, except
that the material in each of the items listed below is informative:
a. Text under a NOTES or Examples heading.
b. Each clause or subclause whose title starts with the word
``Example'' or ``Examples''.
1. All implementations shall conform to the core language. In addition, an
implementation may conform separately to one or more Specialized Needs
Annexes.
2. The following Annexes are informative:
a. Annex K, ``Language-Defined Attributes''
b. Annex L, ``Language-Defined Pragmas''
c. Annex M, ``Implementation-Defined Characteristics''
d. Annex N, ``Glossary''
e. Annex P, ``Syntax Summary''
1. Each section is divided into clauses and subclauses that have a common
structure. Each section, clause, and subclause first introduces its
subject. After the introductory text, text is labeled with the following
headings:
Syntax
2. Syntax rules (indented).
Name Resolution Rules
3. Compile-time rules that are used in name resolution, including overload
resolution.
Legality Rules
4. Rules that are enforced at compile time. A construct is legal if it obeys
all of the Legality Rules.
Static Semantics
5. A definition of the compile-time effect of each construct.
Post-Compilation Rules
6. Rules that are enforced before running a partition. A partition is legal
if its compilation units are legal and it obeys all of the
Post-Compilation Rules.
Dynamic Semantics
7. A definition of the run-time effect of each construct.
Bounded (Run-Time) Errors
8. Situations that result in bounded (run-time) errors, see 1.1.5.
Erroneous Execution
9. Situations that result in erroneous execution, see 1.1.5.
Implementation Requirements
10. Additional requirements for conforming implementations.
Documentation Requirements
11. Documentation requirements for conforming implementations.
Metrics
12. Metrics that are specified for the time/space properties of the execution
of certain language constructs.
Implementation Permissions
13. Additional permissions given to the implementer.
Implementation Advice
14. Optional advice given to the implementer. The word ``should'' is used to
indicate that the advice is a recommendation, not a requirement. It is
implementation defined whether or not a given recommendation is obeyed.
NOTES
15. (1) Notes emphasize consequences of the rules described in the
(sub)clause or elsewhere. This material is informative.
Examples
16. Examples illustrate the possible forms of the constructs described. This
material is informative.
ΓòÉΓòÉΓòÉ 4.1.3. Conformity of an Implementation with the Standard ΓòÉΓòÉΓòÉ
Implementation Requirements
1. A conforming implementation shall:
a. Translate and correctly execute legal programs written in Ada,
provided that they are not so large as to exceed the capacity of the
implementation;
b. Identify all programs or program units that are so large as to
exceed the capacity of the implementation (or raise an appropriate
exception at run time);
c. Identify all programs or program units that contain errors whose
detection is required by this International Standard;
d. Supply all language-defined library units required by this
International Standard;
e. Contain no variations except those explicitly permitted by this
International Standard, or those that are impossible or impractical
to avoid given the implementation's execution environment;
f. Specify all such variations in the manner prescribed by this
International Standard.
1. The external effect of the execution of an Ada program is defined in
terms of its interactions with its external environment. The following
are defined as external interactions:
a. Any interaction with an external file, see A.7,
b. The execution of certain code_statements, see 13.8, which
code_statements cause external interactions is implementation
defined.
c. Any call on an imported subprogram, see B, including any parameters
passed to it;
d. Any result returned or exception propagated from a main subprogram
(see 10.2) or an exported subprogram, see B, to an external caller;
e. Any read or update of an atomic or volatile object, see C.6,
f. The values of imported and exported objects, see B, at the time of
any other interaction with the external environment.
1. A conforming implementation of this International Standard shall produce
for the execution of a given Ada program a set of interactions with the
external environment whose order and timing are consistent with the
definitions and requirements of this International Standard for the
semantics of the given program.
2. An implementation that conforms to this Standard shall support each
capability required by the core language as specified. In addition, an
implementation that conforms to this Standard may conform to one or more
Specialized Needs Annexes (or to none). Conformance to a Specialized
Needs Annex means that each capability required by the Annex is provided
as specified.
3. An implementation conforming to this International Standard may provide
additional attributes, library units, and pragmas. However, it shall not
provide any attribute, library unit, or pragma having the same name as an
attribute, library unit, or pragma (respectively) specified in a
Specialized Needs Annex unless the provided construct is either as
specified in the Specialized Needs Annex or is more limited in capability
than that required by the Annex. A program that attempts to use an
unsupported capability of an Annex shall either be identified by the
implementation before run time or shall raise an exception at run time.
Documentation Requirements
4. Certain aspects of the semantics are defined to be either implementation
defined or unspecified. In such cases, the set of possible effects is
specified, and the implementation may choose any effect in the set.
Implementations shall document their behavior in implementation-defined
situations, but documentation is not required for unspecified situations.
The implementation-defined characteristics are summarized in Annex M.
5. The implementation may choose to document implementation-defined behavior
either by documenting what happens in general, or by providing some
mechanism for the user to determine what happens in a particular case.
Implementation Advice
6. If an implementation detects the use of an unsupported Specialized Needs
Annex feature at run time, it should raise Program_Error if feasible.
7. If an implementation wishes to provide implementation-defined extensions
to the functionality of a language-defined library unit, it should
normally do so by adding children to the library unit.
NOTES
8. (2) The above requirements imply that an implementation conforming to
this Standard may support some of the capabilities required by a
Specialized Needs Annex without supporting all required capabilities.
ΓòÉΓòÉΓòÉ 4.1.4. Method of Description and Syntax Notation ΓòÉΓòÉΓòÉ
1. The form of an Ada program is described by means of a context-free syntax
together with context-dependent requirements expressed by narrative
rules.
2. The meaning of Ada programs is described by means of narrative rules
defining both the effects of each construct and the composition rules for
constructs.
3. The context-free syntax of the language is described using a simple
variant of Backus-Naur Form. In particular:
a. Lower case words in a sans-serif font, some containing embedded
underlines, are used to denote syntactic categories, for example:
b.
case_statement
c. Boldface words are used to denote reserved words, for example:
d.
array
e. Square brackets enclose optional items. Thus the two following rules
are equivalent.
f.
return_statement ::= return [expression];
return_statement ::= return; | return expression;
g. Curly brackets enclose a repeated item. The item may appear zero or
more times; the repetitions occur from left to right as with an
equivalent left-recursive rule. Thus the two following rules are
equivalent.
h.
term ::= factor {multiplying_operator factor}
term ::= factor | term multiplying_operator factor
i. A vertical line separates alternative items unless it occurs
immediately after an opening curly bracket, in which case it stands
for itself:
j.
constraint ::= scalar_constraint | composite_constraint
discrete_choice_list ::= discrete_choice {| discrete_choice}
k. If the name of any syntactic category starts with an italicized
part, it is equivalent to the category name without the italicized
part. The italicized part is intended to convey some semantic
information. For example subtype_name and task_name are both
equivalent to name alone.
1. A syntactic category is a nonterminal in the grammar defined in BNF under
``Syntax.'' Names of syntactic categories are set in a different font,
like_this.
2. A construct is a piece of text (explicit or implicit) that is an instance
of a syntactic category defined under ``Syntax.''
3. A constituent of a construct is the construct itself, or any construct
appearing within it.
4. Whenever the run-time semantics defines certain actions to happen in an
arbitrary order, this means that the implementation shall arrange for
these actions to occur in a way that is equivalent to some sequential
order, following the rules that result from that sequential order. When
evaluations are defined to happen in an arbitrary order, with conversion
of the results to some subtypes, or with some run-time checks, the
evaluations, conversions, and checks may be arbitrarily interspersed, so
long as each expression is evaluated before converting or checking its
value. Note that the effect of a program can depend on the order chosen
by the implementation. This can happen, for example, if two actual
parameters of a given call have side effects.
NOTES
5. (3) The syntax rules describing structured constructs are presented in a
form that corresponds to the recommended paragraphing. For example, an
if_statement is defined as:
6.
if_statement ::=
if condition then
sequence_of_statements
{elsif condition then
sequence_of_statements}
[else
sequence_of_statements]
end if;
7. (4) The line breaks and indentation in the syntax rules indicate the
recommended line breaks and indentation in the corresponding constructs.
The preferred places for other line breaks are after semicolons.
ΓòÉΓòÉΓòÉ 4.1.5. Classification of Errors ΓòÉΓòÉΓòÉ
Implementation Requirements
1. The language definition classifies errors into several different
categories:
a. Errors that are required to be detected prior to run time by every
Ada implementation;
1. These errors correspond to any violation of a rule given in
this International Standard, other than those listed below. In
particular, violation of any rule that uses the terms shall,
allowed, permitted, legal, or illegal belongs to this category.
Any program that contains such an error is not a legal Ada
program; on the other hand, the fact that a program is legal
does not mean, per se, that the program is free from other
forms of error.
2. The rules are further classified as either compile time rules,
or post compilation rules, depending on whether a violation has
to be detected at the time a compilation unit is submitted to
the compiler, or may be postponed until the time a compilation
unit is incorporated into a partition of a program.
a. Errors that are required to be detected at run time by the execution
of an Ada program;
1. The corresponding error situations are associated with the
names of the predefined exceptions. Every Ada compiler is
required to generate code that raises the corresponding
exception if such an error situation arises during program
execution. If such an error situation is certain to arise in
every execution of a construct, then an implementation is
allowed (although not required) to report this fact at
compilation time.
a. Bounded errors;
1. The language rules define certain kinds of errors that need not
be detected either prior to or during run time, but if not
detected, the range of possible effects shall be bounded. The
errors of this category are called bounded errors. The possible
effects of a given bounded error are specified for each such
error, but in any case one possible effect of a bounded error
is the raising of the exception Program_Error.
a. Erroneous execution.
1. In addition to bounded errors, the language rules define
certain kinds of errors as leading to erroneous execution. Like
bounded errors, the implementation need not detect such errors
either prior to or during run time. Unlike bounded errors,
there is no language-specified bound on the possible effect of
erroneous execution; the effect is in general not predictable.
Implementation Permissions
1. An implementation may provide nonstandard modes of operation. Typically
these modes would be selected by a pragma or by a command line switch
when the compiler is invoked. When operating in a nonstandard mode, the
implementation may reject compilation_units that do not conform to
additional requirements associated with the mode, such as an excessive
number of warnings or violation of coding style guidelines. Similarly, in
a nonstandard mode, the implementation may apply special optimizations or
alternative algorithms that are only meaningful for programs that satisfy
certain criteria specified by the implementation. In any case, an
implementation shall support a standard mode that conforms to the
requirements of this International Standard; in particular, in the
standard mode, all legal compilation_units shall be accepted.
Implementation Advice
2. If an implementation detects a bounded error or erroneous execution, it
should raise Program_Error.
ΓòÉΓòÉΓòÉ 4.2. Normative References ΓòÉΓòÉΓòÉ
1. The following standards contain provisions which, through reference in
this text, constitute provisions of this International Standard. At the
time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this
International Standard are encouraged to investigate the possibility of
applying the most recent editions of the standards indicated below.
Members of IEC and ISO maintain registers of currently valid
International Standards.
2. ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set
for information interchange.
3. ISO/IEC 1539:1991, Information technology -- Programming languages --
FORTRAN.
4. ISO 1989:1985, Programming languages -- COBOL.
5. ISO/IEC 6429:1992, Information technology -- Control functions for coded
graphic character sets.
6. ISO/IEC 8859-1:1987, Information processing -- 8-bit single-byte coded
character sets -- Part 1: Latin alphabet No. 1.
7. ISO/IEC 9899:1990, Programming languages -- C.
8. ISO/IEC 10646-1:1993, Information technology -- Universal Multiple-Octet
Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual
Plane.
ΓòÉΓòÉΓòÉ 4.3. Definitions ΓòÉΓòÉΓòÉ
1. Terms are defined throughout this International Standard, indicated by
italic type. Terms explicitly defined in this International Standard are
not to be presumed to refer implicitly to similar terms defined
elsewhere. Terms not defined in this International Standard are to be
interpreted according to the Webster's Third New International Dictionary
of the English Language. Informal descriptions of some terms are also
given in Annex N, ``Glossary''.
ΓòÉΓòÉΓòÉ 5. Lexical Elements ΓòÉΓòÉΓòÉ
1. The text of a program consists of the texts of one or more compilations.
The text of a compilation is a sequence of lexical elements, each
composed of characters; the rules of composition are given in this
section. Pragmas, which provide certain information for the compiler, are
also described in this section.
2.1 Character Set
2.2 Lexical Elements, Separators, and Delimiters
2.3 Identifiers
2.4 Numeric Literals
2.5 Character Literals
2.6 String Literals
2.7 Comments
2.8 Pragmas
2.9 Reserved Words --- The Detailed Node Listing ---
2 Lexical Elements
2.1 Character Set
2.2 Lexical Elements, Separators, and Delimiters
2.3 Identifiers
2.4 Numeric Literals
2.4.1 Decimal Literals
2.4.2 Based Literals
2.5 Character Literals
2.6 String Literals
2.7 Comments
2.8 Pragmas
2.9 Reserved Words
ΓòÉΓòÉΓòÉ 5.1. Character Set ΓòÉΓòÉΓòÉ
1. The only characters allowed outside of comments are the
graphic_characters and format_effectors.
Syntax
2.
character ::=
graphic_character
| format_effector
| other_control_function
3.
graphic_character ::=
identifier_letter
| digit
| space_character
| special_character
Static Semantics
4. The character repertoire for the text of an Ada program consists of the
collection of characters called the Basic Multilingual Plane (BMP) of the
ISO 10646 Universal Multiple-Octet Coded Character Set, plus a set of
format_ effectors and, in comments only, a set of
other_control_functions; the coded representation for these characters is
implementation defined (it need not be a representation defined within
ISO-10646-1).
5. The description of the language definition in this International Standard
uses the graphic symbols defined for Row 00: Basic Latin and Row 00:
Latin-1 Supplement of the ISO 10646 BMP; these correspond to the graphic
symbols of ISO 8859-1 (Latin-1); no graphic symbols are used in this
International Standard for characters outside of Row 00 of the BMP. The
actual set of graphic symbols used by an implementation for the visual
representation of the text of an Ada program is not specified.
6. The categories of characters are defined as follows:
7. identifier_letter
upper_case_identifier_letter | lower_case_identifier_letter
8. upper_case_identifier_letter
Any character of Row 00 of ISO 10646 BMP whose name begins ``Latin
Capital Letter''.
9. lower_case_identifier_letter
Any character of Row 00 of ISO 10646 BMP whose name begins
``Latin Small Letter''.
10. digit
One of the characters 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9.
11. space_character
The character of ISO 10646 BMP named ``Space''.
12. special_character
Any character of the ISO 10646 BMP that is not reserved for a
control function, and is not the space_character, an
identifier_letter, or a digit.
13. format_effector
The control functions of ISO 6429 called character tabulation
(HT), line tabulation (VT), carriage return (CR), line feed (LF),
and form feed (FF).
14. other_control_function
Any control function, other than a format_effector, that is
allowed in a comment; the set of other_control_functions allowed
in comments is implementation defined.
15. The following names are used when referring to certain
special_characters:
symbol name symbol name
" quotation mark : colon
# number sign ; semicolon
& ampersand < less-than sign
' apostrophe, tick = equals sign
( left parenthesis > greater-than sign
) right parenthesis _ low line, underline
* asterisk, multiply | vertical line
+ plus sign [ left square bracket
, comma ] right square bracket
- hyphen-minus, minus { left curly bracket
. full stop, dot, point } right curly bracket
/ solidus, divide
Implementation Permissions
16. In a nonstandard mode, the implementation may support a different
character repertoire; in particular, the set of characters that are
considered identifier_letters can be extended or changed to conform to
local conventions.
NOTES
17. (1) Every code position of ISO 10646 BMP that is not reserved for a
control function is defined to be a graphic_character by this
International Standard. This includes all code positions other than 0000
- 001F, 007F - 009F, and FFFE - FFFF.
18. (2) The language does not specify the source representation of programs.
ΓòÉΓòÉΓòÉ 5.2. Lexical Elements, Separators, and Delimiters ΓòÉΓòÉΓòÉ
Static Semantics
1. The text of a program consists of the texts of one or more compilations.
The text of each compilation is a sequence of separate lexical elements.
Each lexical element is formed from a sequence of characters, and is
either a delimiter, an identifier, a reserved word, a numeric_literal, a
character_ literal, a string_literal, or a comment. The meaning of a
program depends only on the particular sequences of lexical elements that
form its compilations, excluding comments.
2. The text of a compilation is divided into lines. In general, the
representation for an end of line is implementation defined. However, a
sequence of one or more format_effectors other than character tabulation
(HT) signifies at least one end of line.
3. In some cases an explicit separator is required to separate adjacent
lexical elements. A separator is any of a space character, a format
effector, or the end of a line, as follows:
a. A space character is a separator except within a comment, a
string_literal, or a character_literal.
b. Character tabulation (HT) is a separator except within a comment.
c. The end of a line is always a separator.
1. One or more separators are allowed between any two adjacent lexical
elements, before the first of each compilation, or after the last. At
least one separator is required between an identifier, a reserved word,
or a numeric_literal and an adjacent identifier, reserved word, or
numeric_literal.
2. A delimiter is either one of the following special characters
3.
& ' ( ) * + , -
┬╖ / : ; < = > |
4. or one of the following compound delimiters each composed of two adjacent
special characters
5.
=> ┬╖┬╖ ** := /= >= <= << >> <>
6. Each of the special characters listed for single character delimiters is
a single delimiter except if this character is used as a character of a
compound delimiter, or as a character of a comment, string_literal,
character_literal, or numeric_literal.
7. The following names are used when referring to compound delimiters:
8.
delimiter name
=> arrow
┬╖┬╖ double dot
** double star, exponentiate
:= assignment (pronounced: ``becomes'')
/= inequality (pronounced: ``not equal'')
>= greater than or equal
<= less than or equal
<< left label bracket
>> right label bracket
<> box
Implementation Requirements
9. An implementation shall support lines of at least 200 characters in
length, not counting any characters used to signify the end of a line. An
implementation shall support lexical elements of at least 200 characters
in length. The maximum supported line length and lexical element length
are implementation defined.
ΓòÉΓòÉΓòÉ 5.3. Identifiers ΓòÉΓòÉΓòÉ
1. Identifiers are used as names.
Syntax
2.
identifier ::= identifier_letter {[underline] letter_or_digit}
3.
letter_or_digit ::= identifier_letter | digit
a. An identifier shall not be a reserved word.
Static Semantics
1. All characters of an identifier are significant, including any underline
character. Identifiers differing only in the use of corresponding upper
and lower case letters are considered the same.
Implementation Permissions
2. In a nonstandard mode, an implementation may support other upper/lower
case equivalence rules for identifiers, to accommodate local conventions.
Examples
3. Examples of identifiers:
4.
Count X Get_Symbol Ethelyn Marion
Snobol_4 X1 Page_Count Store_Next_Item
ΓòÉΓòÉΓòÉ 5.4. Numeric Literals ΓòÉΓòÉΓòÉ
1. There are two kinds of numeric_literals, real literals and integer
literals. A real literal is a numeric_literal that includes a point; an
integer literal is a numeric_literal without a point.
Syntax
2.
numeric_literal ::= decimal_literal | based_literal
NOTES
3. (3) The type of an integer literal is universal_integer. The type of a
real literal is universal_real.
2.4.1 Decimal Literals
2.4.2 Based Literals
ΓòÉΓòÉΓòÉ 5.4.1. Decimal Literals ΓòÉΓòÉΓòÉ
1. A decimal_literal is a numeric_literal in the conventional decimal
notation (that is, the base is ten).
Syntax
2.
decimal_literal ::= numeral [.numeral] [exponent]
3.
numeral ::= digit {[underline] digit}
4.
exponent ::= E [+] numeral | E - numeral
a. An exponent for an integer literal shall not have a minus sign.
Static Semantics
1. An underline character in a numeric_literal does not affect its meaning.
The letter E of an exponent can be written either in lower case or in
upper case, with the same meaning.
2. An exponent indicates the power of ten by which the value of the
decimal_literal without the exponent is to be multiplied to obtain the
value of the decimal_literal with the exponent.
Examples
3. Examples of decimal literals:
4.
12 0 1E6 123_456 -- integer literals
12.0 0.0 0.456 3.14159_26 -- real literals
ΓòÉΓòÉΓòÉ 5.4.2. Based Literals ΓòÉΓòÉΓòÉ
1. A based_literal is a numeric_literal expressed in a form that specifies
the base explicitly.
Syntax
2.
based_literal ::= base # based_numeral [.based_numeral] # [exponent]
3.
base ::= numeral
4.
based_numeral ::=
extended_digit {[underline] extended_digit}
5.
extended_digit ::= digit | A | B | C | D | E | F
Legality Rules
6. The base (the numeric value of the decimal numeral preceding the first #)
shall be at least two and at most sixteen. The extended_digits A through
F represent the digits ten through fifteen, respectively. The value of
each extended_digit of a based_literal shall be less than the base.
Static Semantics
7. The conventional meaning of based notation is assumed. An exponent
indicates the power of the base by which the value of the based_literal
without the exponent is to be multiplied to obtain the value of the
based_literal with the exponent. The base and the exponent, if any, are
in decimal notation.
8. The extended_digits A through F can be written either in lower case or in
upper case, with the same meaning.
Examples
9. Examples of based literals:
10.
2#1111_1111# 16#FF# 016#0ff#
-- integer literals of value 255
16#E#E1 2#1110_0000#
-- integer literals of value 224
16#F.FF#E+2 2#1.1111_1111_1110#E11
-- real literals of value 4095.0
ΓòÉΓòÉΓòÉ 5.5. Character Literals ΓòÉΓòÉΓòÉ
1. A character_literal is formed by enclosing a graphic character between
two apostrophe characters.
Syntax
2.
character_literal ::= 'graphic_character'
NOTES
3. (4) A character_literal is an enumeration literal of a character type.
(see 3.5.2).
Examples
4. Examples of character literals:
5.
'A' '*' ''' ' '
ΓòÉΓòÉΓòÉ 5.6. String Literals ΓòÉΓòÉΓòÉ
1. A string_literal is formed by a sequence of graphic characters (possibly
none) enclosed between two quotation marks used as string brackets. They
are used to represent operator_symbols (see 6.1) values of a string type
(see 4.2) and array subaggregates (see 4.3.3).
Syntax
2.
string_literal ::= "{string_element}"
3.
string_element ::= "" | non_quotation_mark_graphic_character
a. A string_element is either a pair of quotation marks (""), or a
single graphic_character other than a quotation mark.
Static Semantics
1. The sequence of characters of a string_literal is formed from the
sequence of string_elements between the bracketing quotation marks, in
the given order, with a string_element that is "" becoming a single
quotation mark in the sequence of characters, and any other
string_element being reproduced in the sequence.
2. A null string literal is a string_literal with no string_elements between
the quotation marks.
NOTES
3. (5) An end of line cannot appear in a string_literal.
Examples
4. Examples of string literals:
5.
"Message of the day:"
"" -- a null string literal
" " "A" """" -- three string literals of length 1
"Characters such as $, %, and } are allowed in string literals"
ΓòÉΓòÉΓòÉ 5.7. Comments ΓòÉΓòÉΓòÉ
1. A comment starts with two adjacent hyphens and extends up to the end of
the line.
Syntax
2.
comment ::= --{non_end_of_line_character}
a. A comment may appear on any line of a program.
Static Semantics
1. The presence or absence of comments has no influence on whether a program
is legal or illegal. Furthermore, comments do not influence the meaning
of a program; their sole purpose is the enlightenment of the human
reader.
Examples
2. Examples of comments:
3.
-- the last sentence above echoes the Algol 68 report
end; -- processing of Line is complete
-- a long comment may be split onto
-- two or more consecutive lines
---------------- the first two hyphens start the comment
ΓòÉΓòÉΓòÉ 5.8. Pragmas ΓòÉΓòÉΓòÉ
1. A pragma is a compiler directive. There are language-defined pragmas that
give instructions for optimization, listing control, etc. An
implementation may support additional (implementation-defined) pragmas.
Syntax
2.
pragma ::=
pragma identifier [(pragma_argument_association
{, pragma_argument_association})];
3.
pragma_argument_association ::=
[pragma_argument_identifier =>] name
| [pragma_argument_identifier =>] expression
a. In a pragma, any pragma_argument_associations without a
pragma_argument_identifier shall precede any associations with a
pragma_argument_identifier.
b. Pragmas are only allowed at the following places in a program:
1. After a semicolon delimiter, but not within a formal_part or
discriminant_part.
2. At any place where the syntax rules allow a construct defined
by a syntactic category whose name ends with "declaration",
"statement", "clause", or "alternative", or one of the
syntactic categories variant or exception_handler; but not in
place of such a construct. Also at any place where a
compilation_unit would be allowed.
a. Additional syntax rules and placement restrictions exist for
specific pragmas.
1. The name of a pragma is the identifier following the reserved word
pragma. The name or expression of a pragma_argument_association is a
pragma argument.
2. An identifier specific to a pragma is an identifier that is used in a
pragma argument with special meaning for that pragma.
Static Semantics
3. If an implementation does not recognize the name of a pragma, then it has
no effect on the semantics of the program. Inside such a pragma, the only
rules that apply are the Syntax Rules.
Dynamic Semantics
4. Any pragma that appears at the place of an executable construct is
executed. Unless otherwise specified for a particular pragma, this
execution consists of the evaluation of each evaluable pragma argument in
an arbitrary order.
Implementation Requirements
5. The implementation shall give a warning message for an unrecognized
pragma name.
Implementation Permissions
6. An implementation may provide implementation-defined pragmas; the name of
an implementation-defined pragma shall differ from those of the
language-defined pragmas.
7. An implementation may ignore an unrecognized pragma even if it violates
some of the Syntax Rules, if detecting the syntax error is too complex.
Implementation Advice
8. Normally, implementation-defined pragmas should have no semantic effect
for error-free programs; that is, if the implementation-defined pragmas
are removed from a working program, the program should still be legal,
and should still have the same semantics.
9. Normally, an implementation should not define pragmas that can make an
illegal program legal, except as follows:
a. A pragma used to complete a declaration, such as a pragma Import;
b. A pragma used to configure the environment by adding, removing, or
replacing library_items.
Syntax
1. The forms of List, Page, and Optimize pragmas are as follows:
2. pragma List(identifier);
3. pragma Page;
4. pragma Optimize(identifier);
a. Other pragmas are defined throughout this International Standard,
and are summarized in Annex L.
Static Semantics
1. A pragma List takes one of the identifiers On or Off as the single
argument. This pragma is allowed anywhere a pragma is allowed. It
specifies that listing of the compilation is to be continued or suspended
until a List pragma with the opposite argument is given within the same
compilation. The pragma itself is always listed if the compiler is
producing a listing.
2. A pragma Page is allowed anywhere a pragma is allowed. It specifies that
the program text which follows the pragma should start on a new page (if
the compiler is currently producing a listing).
3. A pragma Optimize takes one of the identifiers Time, Space, or Off as the
single argument. This pragma is allowed anywhere a pragma is allowed, and
it applies until the end of the immediately enclosing declarative region,
or for a pragma at the place of a compilation_unit, to the end of the
compilation. It gives advice to the implementation as to whether time or
space is the primary optimization criterion, or that optional
optimizations should be turned off. It is implementation defined how this
advice is followed.
Examples
4. Examples of pragmas:
5.
pragma List(Off); -- turn off listing generation
pragma Optimize(Off); -- turn off optional optimizations
pragma Inline(Set_Mask); -- generate code for Set_Mask inline
pragma Suppress(Range_Check, On => Index);
-- turn off range checking on Index
ΓòÉΓòÉΓòÉ 5.9. Reserved Words ΓòÉΓòÉΓòÉ
Syntax
a. The following are the reserved words (ignoring upper/lower case
distinctions):
abort else new return
abs elsif not reverse
abstract end null
accept entry select
access exception separate
aliased exit of subtype
all or
and for others tagged
array function out task
at terminate
generic package then
begin goto pragma type
body private
if procedure
case in protected until
constant is use
raise
declare range when
delay limited record while
delta loop rem with
digits renames
do mod requeue xor
NOTES
1. (6) The reserved words appear in lower case boldface in this
International Standard, except when used in the designator of an
attribute (see 4.1.4). Lower case boldface is also used for a reserved
word in a string_literal used as an operator_symbol. This is merely a
convention -- programs may be written in whatever typeface is desired and
available.
ΓòÉΓòÉΓòÉ 6. Declarations and Types ΓòÉΓòÉΓòÉ
1. This section describes the types in the language and the rules for
declaring constants, variables, and named numbers.
3.1 Declarations
3.2 Types and Subtypes
3.3 Objects and Named Numbers
3.4 Derived Types and Classes
3.5 Scalar Types
3.6 Array Types
3.7 Discriminants
3.8 Record Types
3.9 Tagged Types and Type Extensions
3.10 Access Types
3.11 Declarative Parts --- The Detailed Node Listing
---
3.1 Declarations
3.2 Types and Subtypes
3.2.1 Type Declarations
3.2.2 Subtype Declarations
3.2.3 Classification of Operations
3.3 Objects and Named Numbers
3.3.1 Object Declarations
3.3.2 Number Declarations
3.4 Derived Types and Classes
3.4.1 Derivation Classes
3.5 Scalar Types
3.5.1 Enumeration Types
3.5.2 Character Types
3.5.3 Boolean Types
3.5.4 Integer Types
3.5.5 Operations of Discrete Types
3.5.6 Real Types
3.5.7 Floating Point Types
3.5.8 Operations of Floating Point Types
3.5.9 Fixed Point Types
3.5.10 Operations of Fixed Point Types
3.6 Array Types
3.6.1 Index Constraints and Discrete Ranges
3.6.2 Operations of Array Types
3.6.3 String Types
3.7 Discriminants
3.7.1 Discriminant Constraints
3.7.2 Operations of Discriminated Types
3.8 Record Types
3.8.1 Variant Parts and Discrete Choices
3.9 Tagged Types and Type Extensions
3.9.1 Type Extensions
3.9.2 Dispatching Operations of Tagged Types
3.9.3 Abstract Types and Subprograms
3.10 Access Types
3.10.1 Incomplete Type Declarations
3.10.2 Operations of Access Types
3.11 Declarative Parts
3.11.1 Completions of Declarations
ΓòÉΓòÉΓòÉ 6.1. Declarations ΓòÉΓòÉΓòÉ
1. The language defines several kinds of named entities that are declared by
declarations. The entity's name is defined by the declaration, usually by
a defining_identifier, but sometimes by a defining_character_literal or
defining_operator_symbol.
2. There are several forms of declaration. A basic_declaration is a form of
declaration defined as follows.
Syntax
3.
basic_declaration ::=
type_declaration | subtype_declaration
| object_declaration | number_declaration
| subprogram_declaration | abstract_subprogram_declaration
| package_declaration | renaming_declaration
| exception_declaration | generic_declaration
| generic_instantiation
4.
defining_identifier ::= identifier
Static Semantics
5. A declaration is a language construct that associates a name with (a view
of) an entity. A declaration may appear explicitly in the program text
(an explicit declaration), or may be supposed to occur at a given place
in the text as a consequence of the semantics of another construct (an
implicit declaration).
6. Each of the following is defined to be a declaration: any
basic_declaration; an enumeration_literal_specification; a
discriminant_specification; a component_declaration; a
loop_parameter_specification; a parameter_specification; a
subprogram_body; an entry_declaration; an entry_index_specification; a
choice_parameter_specification; a generic_formal_parameter_declaration.
7. All declarations contain a definition for a view of an entity. A view
consists of an identification of the entity (the entity of the view),
plus view-specific characteristics that affect the use of the entity
through that view (such as mode of access to an object, formal parameter
names and defaults for a subprogram, or visibility to components of a
type). In most cases, a declaration also contains the definition for the
entity itself (a renaming_declaration is an example of a declaration that
does not define a new entity, but instead defines a view of an existing
entity, see 8.5.)
8. For each declaration, the language rules define a certain region of text
called the scope of the declaration (see 8.2). Most declarations
associate an identifier with a declared entity. Within its scope, and
only there, there are places where it is possible to use the identifier
to refer to the declaration, the view it defines, and the associated
entity; these places are defined by the visibility rules (see 8.3). At
such places the identifier is said to be a name of the entity (the
direct_name or selector_name); the name is said to denote the
declaration, the view, and the associated entity (see 8.6). The
declaration is said to declare the name, the view, and in most cases, the
entity itself.
9. As an alternative to an identifier, an enumeration literal can be
declared with a character_literal as its name (see 3.5.1) and a function
can be declared with an operator_symbol as its name (see 6.1).
10. The syntax rules use the terms defining_identifier,
defining_character_literal, and defining_operator_symbol for the defining
occurrence of a name; these are collectively called defining names. The
terms direct_name and selector_name are used for usage occurrences of
identifiers, character_literals, and operator_symbols. These are
collectively called usage names.
Dynamic Semantics
11. The process by which a construct achieves its run-time effect is called
execution. This process is also called elaboration for declarations and
evaluation for expressions. One of the terms execution, elaboration, or
evaluation is defined by this International Standard for each construct
that has a run-time effect.
NOTES
12. (1) At compile time, the declaration of an entity declares the entity. At
run time, the elaboration of the declaration creates the entity.
ΓòÉΓòÉΓòÉ 6.2. Types and Subtypes ΓòÉΓòÉΓòÉ
Static Semantics
1. A type is characterized by a set of values, and a set of primitive
operations which implement the fundamental aspects of its semantics. An
object of a given type is a run-time entity that contains (has) a value
of the type.
2. Types are grouped into classes of types, reflecting the similarity of
their values and primitive operations. There exist several
language-defined classes of types (see NOTES below). Elementary types are
those whose values are logically indivisible; composite types are those
whose values are composed of component values.
3. The elementary types are the scalar types (discrete and real) and the
access types (whose values provide access to objects or subprograms).
Discrete types are either integer types or are defined by enumeration of
their values (enumeration types). Real types are either floating point
types or fixed point types.
4. The composite types are the record types, record extensions, array types,
task types, and protected types. A private type or private extension
represents a partial view, see 7.3, of a type, providing support for data
abstraction. A partial view is a composite type.
5. Certain composite types (and partial views thereof) have special
components called discriminants whose values affect the presence,
constraints, or initialization of other components. Discriminants can be
thought of as parameters of the type.
6. The term subcomponent is used in this International Standard in place of
the term component to indicate either a component, or a component of
another subcomponent. Where other subcomponents are excluded, the term
component is used instead. Similarly, a part of an object or value is
used to mean the whole object or value, or any set of its subcomponents.
7. The set of possible values for an object of a given type can be subjected
to a condition that is called a constraint (the case of a null constraint
that specifies no restriction is also included); the rules for which
values satisfy a given kind of constraint are given in 3.5 for
range_constraints, 3.6.1, for index_constraints, and 3.7.1, for
discriminant_constraints.
8. A subtype of a given type is a combination of the type, a constraint on
values of the type, and certain attributes specific to the subtype. The
given type is called the type of the subtype. Similarly, the associated
constraint is called the constraint of the subtype. The set of values of
a subtype consists of the values of its type that satisfy its constraint.
Such values belong to the subtype.
9. A subtype is called an unconstrained subtype if its type has unknown
discriminants, or if its type allows range, index, or discriminant
constraints, but the subtype does not impose such a constraint;
otherwise, the subtype is called a constrained subtype (since it has no
unconstrained characteristics).
NOTES
10. (2) Any set of types that is closed under derivation (see 3.4) can be
called a ``class'' of types. However, only certain classes are used in
the description of the rules of the language -- generally those that have
their own particular set of primitive operations (see 3.2.3) or that
correspond to a set of types that are matched by a given kind of generic
formal type (see 12.5). The following are examples of ``interesting''
language-defined classes: elementary, scalar, discrete, enumeration,
character, boolean, integer, signed integer, modular, real, floating
point, fixed point, ordinary fixed point, decimal fixed point, numeric,
access, access-to-object, access-to-subprogram, composite, array, string,
(untagged) record, tagged, task, protected, nonlimited. Special syntax is
provided to define types in each of these classes.
a. These language-defined classes are organized like this:
b.
all types
elementary
scalar
discrete
enumeration
character
boolean
other enumeration
integer
signed integer
modular integer
real
floating point
fixed point
ordinary fixed point
decimal fixed point
access
access-to-object
access-to-subprogram
composite
array
string
other array
untagged record
tagged
task
protected
c. The classes ``numeric'' and ``nonlimited'' represent other
classification dimensions and do not fit into the above strictly
hierarchical picture.
3.2.1 Type Declarations
3.2.2 Subtype Declarations
3.2.3 Classification of Operations
ΓòÉΓòÉΓòÉ 6.2.1. Type Declarations ΓòÉΓòÉΓòÉ
1. A type_declaration declares a type and its first subtype.
Syntax
2.
type_declaration ::=
full_type_declaration
| incomplete_type_declaration
| private_type_declaration
| private_extension_declaration
3.
full_type_declaration ::=
type defining_identifier [known_discriminant_part]
is type_definition;
| task_type_declaration
| protected_type_declaration
4.
type_definition ::=
enumeration_type_definition | integer_type_definition
| real_type_definition | array_type_definition
| record_type_definition | access_type_definition
| derived_type_definition
Legality Rules
5. A given type shall not have a subcomponent whose type is the given type
itself.
Static Semantics
6. The defining_identifier of a type_declaration denotes the first subtype
of the type. The known_discriminant_part, if any, defines the
discriminants of the type (see 3.7: ``Discriminants''). The remainder of
the type_ declaration defines the remaining characteristics of (the view
of) the type.
7. A type defined by a type_declaration is a named type; such a type has one
or more nameable subtypes. Certain other forms of declaration also
include type definitions as part of the declaration for an object
(including a parameter or a discriminant). The type defined by such a
declaration is anonymous -- it has no nameable subtypes. For explanatory
purposes, this International Standard sometimes refers to an anonymous
type by a pseudo-name, written in italics, and uses such pseudo-names at
places where the syntax normally requires an identifier. For a named type
whose first subtype is T, this International Standard sometimes refers to
the type of T as simply ``the type T.''
8. A named type that is declared by a full_type_declaration, or an anonymous
type that is defined as part of declaring an object of the type, is
called a full type. The type_definition, task_definition,
protected_definition, or access_definition that defines a full type is
called a full type definition. Types declared by other forms of
type_declaration are not separate types; they are partial or incomplete
views of some full type.
9. The definition of a type implicitly declares certain predefined operators
that operate on the type, according to what classes the type belongs, as
specified in 4.5: ``Operators and Expression Evaluation''.
10. The predefined types (for example the types Boolean, Wide_Character,
Integer, root_integer, and universal_integer) are the types that are
defined in a predefined library package called Standard; this package
also includes the (implicit) declarations of their predefined operators.
The package Standard is described in A.1.
Dynamic Semantics
11. The elaboration of a full_type_declaration consists of the elaboration of
the full type definition. Each elaboration of a full type definition
creates a distinct type and its first subtype.
Examples
12. Examples of type definitions:
13.
(White, Red, Yellow, Green, Blue, Brown, Black)
range 1 ┬╖┬╖ 72
array(1 ┬╖┬╖ 10) of Integer
14. Examples of type declarations:
15.
type Color is (White, Red, Yellow, Green, Blue, Brown, Black);
type Column is range 1 ┬╖┬╖ 72;
type Table is array(1 ┬╖┬╖ 10) of Integer;
NOTES
16. (3) Each of the above examples declares a named type. The identifier
given denotes the first subtype of the type. Other named subtypes of the
type can be declared with subtype_declarations (see 3.2.2). Although
names do not directly denote types, a phrase like ``the type Column'' is
sometimes used in this International Standard to refer to the type of
Column, where Column denotes the first subtype of the type. For an
example of the definition of an anonymous type, see the declaration of
the array Color_Table in 3.3.1, its type is anonymous -- it has no
nameable subtypes.
ΓòÉΓòÉΓòÉ 6.2.2. Subtype Declarations ΓòÉΓòÉΓòÉ
1. A subtype_declaration declares a subtype of some previously declared
type, as defined by a subtype_indication.
Syntax
2.
subtype_declaration ::=
subtype defining_identifier is subtype_indication;
3.
subtype_indication ::= subtype_mark [constraint]
4.
subtype_mark ::= subtype_name
5.
constraint ::= scalar_constraint | composite_constraint
6.
scalar_constraint ::=
range_constraint | digits_constraint | delta_constraint
7.
composite_constraint ::=
index_constraint | discriminant_constraint
Name Resolution Rules
8. A subtype_mark shall resolve to denote a subtype. The type determined by
a subtype_mark is the type of the subtype denoted by the subtype_mark.
Dynamic Semantics
9. The elaboration of a subtype_declaration consists of the elaboration of
the subtype_indication. The elaboration of a subtype_indication creates a
new subtype. If the subtype_indication does not include a constraint, the
new subtype has the same (possibly null) constraint as that denoted by
the subtype_mark. The elaboration of a subtype_indication that includes a
constraint proceeds as follows:
a. The constraint is first elaborated.
b. A check is then made that the constraint is compatible with the
subtype denoted by the subtype_mark.
1. The condition imposed by a constraint is the condition obtained after
elaboration of the constraint. The rules defining compatibility are given
for each form of constraint in the appropriate subclause. These rules are
such that if a constraint is compatible with a subtype, then the
condition imposed by the constraint cannot contradict any condition
already imposed by the subtype on its values. The exception
Constraint_Error is raised if any check of compatibility fails.
NOTES
2. (4) A scalar_constraint may be applied to a subtype of an appropriate
scalar type, see 3.5, see 3.5.9, and J.3, even if the subtype is already
constrained. On the other hand, a composite_constraint may be applied to
a composite subtype (or an access-to-composite subtype) only if the
composite subtype is unconstrained, see 3.6.1 and 3.7.1.
Examples
3. Examples of subtype declarations:
4.
subtype Rainbow is Color range Red ┬╖┬╖ Blue; -- see 3.2.1
subtype Red_Blue is Rainbow;
subtype Int is Integer;
subtype Small_Int is Integer range -10 ┬╖┬╖ 10;
subtype Up_To_K is Column range 1 ┬╖┬╖ K; -- see 3.2.1
subtype Square is Matrix(1 ┬╖┬╖ 10, 1 ┬╖┬╖ 10); -- see 3.6
subtype Male is Person(Sex => M); -- see 3.10.1
ΓòÉΓòÉΓòÉ 6.2.3. Classification of Operations ΓòÉΓòÉΓòÉ
Static Semantics
1. An operation operates on a type T if it yields a value of type T, if it
has an operand whose expected type, see 8.6, is T, or if it has an access
parameter, see 6.1 designating T. A predefined operator, or other
language-defined operation such as assignment or a membership test, that
operates on a type, is called a predefined operation of the type. The
primitive operations of a type are the predefined operations of the type,
plus any user-defined primitive subprograms.
2. The primitive subprograms of a specific type are defined as follows:
a. The predefined operators of the type, see 4.5,
b. For a derived type, the inherited, see 3.4, user-defined
subprograms;
c. For an enumeration type, the enumeration literals (which are
considered parameterless functions -- see 3.5.1.);
d. For a specific type declared immediately within a
package_specification, any subprograms (in addition to the
enumeration literals) that are explicitly declared immediately
within the same package_specification and that operate on the type;
e. Any subprograms not covered above that are explicitly declared
immediately within the same declarative region as the type and that
override, see 8.3, other implicitly declared primitive subprograms
of the type.
1. A primitive subprogram whose designator is an operator_symbol is called a
primitive operator.
ΓòÉΓòÉΓòÉ 6.3. Objects and Named Numbers ΓòÉΓòÉΓòÉ
1. Objects are created at run time and contain a value of a given type. An
object can be created and initialized as part of elaborating a
declaration, evaluating an allocator, aggregate, or function_call, or
passing a parameter by copy. Prior to reclaiming the storage for an
object, it is finalized if necessary, see 7.6.1.
Static Semantics
2. All of the following are objects:
a. the entity declared by an object_declaration;
b. a formal parameter of a subprogram, entry, or generic subprogram;
c. a generic formal object;
d. a loop parameter;
e. a choice parameter of an exception_handler;
f. an entry index of an entry_body;
g. the result of dereferencing an access-to-object value, see 4.1,
h. the result of evaluating a function_call (or the equivalent operator
invocation -- see 6.6,
i. the result of evaluating an aggregate;
j. a component, slice, or view conversion of another object.
1. An object is either a constant object or a variable object. The value of
a constant object cannot be changed between its initialization and its
finalization, whereas the value of a variable object can be changed.
Similarly, a view of an object is either a constant or a variable. All
views of a constant object are constant. A constant view of a variable
object cannot be used to modify the value of the variable. The terms
constant and variable by themselves refer to constant and variable views
of objects.
2. The value of an object is read when the value of any part of the object
is evaluated, or when the value of an enclosing object is evaluated. The
value of a variable is updated when an assignment is performed to any
part of the variable, or when an assignment is performed to an enclosing
object.
3. Whether a view of an object is constant or variable is determined by the
definition of the view. The following (and no others) represent
constants:
a. an object declared by an object_declaration with the reserved word
constant;
b. a formal parameter or generic formal object of mode in;
c. a discriminant;
d. a loop parameter, choice parameter, or entry index;
e. the dereference of an access-to-constant value;
f. he result of evaluating a function_call or an aggregate;
g. a selected_component, indexed_component, slice, or view conversion
of a constant.
1. At the place where a view of an object is defined, a nominal subtype is
associated with the view. The object's actual subtype (that is, its
subtype) can be more restrictive than the nominal subtype of the view; it
always is if the nominal subtype is an indefinite subtype. A subtype is
an indefinite subtype if it is an unconstrained array subtype, or if it
has unknown discriminants or unconstrained discriminants without defaults
(see 3.7) otherwise the subtype is a definite subtype (all elementary
subtypes are definite subtypes). A class-wide subtype is defined to have
unknown discriminants, and is therefore an indefinite subtype. An
indefinite subtype does not by itself provide enough information to
create an object; an additional constraint or explicit initialization
expression is necessary (see 3.3.1). A component cannot have an
indefinite nominal subtype.
2. A named number provides a name for a numeric value known at compile time.
It is declared by a number_declaration.
NOTES
3. (5) A constant cannot be the target of an assignment operation, nor be
passed as an in out or out parameter, between its initialization and
finalization, if any.
4. (6) The nominal and actual subtypes of an elementary object are always
the same. For a discriminated or array object, if the nominal subtype is
constrained then so is the actual subtype.
3.3.1 Object Declarations
3.3.2 Number Declarations
ΓòÉΓòÉΓòÉ 6.3.1. Object Declarations ΓòÉΓòÉΓòÉ
1. An object_declaration declares a stand-alone object with a given nominal
subtype and, optionally, an explicit initial value given by an
initialization expression. For an array, task, or protected object, the
object_declaration may include the definition of the (anonymous) type of
the object.
Syntax
2.
object_declaration ::=
defining_identifier_list : [aliased] [constant]
subtype_indication [:= expression];
| defining_identifier_list : [aliased] [constant]
array_type_definition [:= expression];
| single_task_declaration
| single_protected_declaration
3.
defining_identifier_list ::=
defining_identifier {, defining_identifier}
Name Resolution Rules
4. For an object_declaration with an expression following the compound
delimiter :=, the type expected for the expression is that of the object.
This expression is called the initialization expression.
Legality Rules
5. An object_declaration without the reserved word constant declares a
variable object. If it has a subtype_indication or an
array_type_definition that defines an indefinite subtype, then there
shall be an initialization expression. An initialization expression shall
not be given if the object is of a limited type.
Static Semantics
6. An object_declaration with the reserved word constant declares a constant
object. If it has an initialization expression, then it is called a full
constant declaration. Otherwise it is called a deferred constant
declaration. The rules for deferred constant declarations are given in
clause (see 7.4). The rules for full constant declarations are given in
this subclause.
7. Any declaration that includes a defining_identifier_list with more than
one defining_identifier is equivalent to a series of declarations each
containing one defining_identifier from the list, with the rest of the
text of the declaration copied for each declaration in the series, in the
same order as the list. The remainder of this International Standard
relies on this equivalence; explanations are given for declarations with
a single defining_identifier.
8. The subtype_indication or full type definition of an object_declaration
defines the nominal subtype of the object. The object_declaration
declares an object of the type of the nominal subtype.
Dynamic Semantics
9. If a composite object declared by an object_declaration has an
unconstrained nominal subtype, then if this subtype is indefinite or the
object is constant or aliased, see 3.10, the actual subtype of this
object is constrained. The constraint is determined by the bounds or
discriminants (if any) of its initial value; the object is said to be
constrained by its initial value. In the case of an aliased object, this
initial value may be either explicit or implicit; in the other cases, an
explicit initial value is required. When not constrained by its initial
value, the actual and nominal subtypes of the object are the same. If its
actual subtype is constrained, the object is called a constrained object.
10. For an object_declaration without an initialization expression, any
initial values for the object or its subcomponents are determined by the
implicit initial values defined for its nominal subtype, as follows:
a. The implicit initial value for an access subtype is the null value
of the access type.
b. The implicit initial (and only) value for each discriminant of a
constrained discriminated subtype is defined by the subtype.
c. For a (definite) composite subtype, the implicit initial value of
each component with a default_expression is obtained by evaluation
of this expression and conversion to the component's nominal subtype
(which might raise Constraint_Error -- see 4.6: ``Type
Conversions''.), unless the component is a discriminant of a
constrained subtype (the previous case), or is in an excluded
variant, see 3.8.1. For each component that does not have a
default_expression, any implicit initial values are those determined
by the component's nominal subtype.
d. For a protected or task subtype, there is an implicit component (an
entry queue) corresponding to each entry, with its implicit initial
value being an empty queue.
1. The elaboration of an object_declaration proceeds in the following
sequence of steps:
a. The subtype_indication, array_type_definition,
single_task_declaration, or single_protected_declaration is first
elaborated. This creates the nominal subtype (and the anonymous type
in the latter three cases).
b. If the object_declaration includes an initialization expression, the
(explicit) initial value is obtained by evaluating the expression
and converting it to the nominal subtype (which might raise
Constraint_Error -- see 4.6.).
c. The object is created, and, if there is not an initialization
expression, any per-object expressions, see 3.8 are evaluated and
any implicit initial values for the object or for its subcomponents
are obtained as determined by the nominal subtype.
d. Any initial values (whether explicit or implicit) are assigned to
the object or to the corresponding subcomponents. As described in
5.2, and 7.6, Initialize and Adjust procedures can be called.
1. For the third step above, the object creation and any elaborations and
evaluations are performed in an arbitrary order, except that if the
default_expression for a discriminant is evaluated to obtain its initial
value, then this evaluation is performed before that of the
default_expression for any component that depends on the discriminant,
and also before that of any default_expression that includes the name of
the discriminant. The evaluations of the third step and the assignments
of the fourth step are performed in an arbitrary order, except that each
evaluation is performed before the resulting value is assigned.
2. There is no implicit initial value defined for a scalar subtype. In the
absence of an explicit initialization, a newly created scalar object
might have a value that does not belong to its subtype (see 13.9.1 and
H.1).
NOTES
3. (7) Implicit initial values are not defined for an indefinite subtype,
because if an object's nominal subtype is indefinite, an explicit initial
value is required.
4. (8) As indicated above, a stand-alone object is an object declared by an
object_declaration. Similar definitions apply to ``stand-alone constant''
and ``stand-alone variable.'' A subcomponent of an object is not a
stand-alone object, nor is an object that is created by an allocator. An
object declared by a loop_parameter_specification,
parameter_specification, entry_index_specification,
choice_parameter_specification, or a formal_object_declaration is not
called a stand-alone object.
5. (9) The type of a stand-alone object cannot be abstract, see 3.9.3.
Examples
6. Example of a multiple object declaration:
7.
-- the multiple object declaration
8.
John, Paul : Person_Name := new Person(Sex => M); -- see 3.10.1
9.
-- is equivalent to the two single object
-- declarations in the order given
10.
John : Person_Name := new Person(Sex => M);
Paul : Person_Name := new Person(Sex => M);
11. Examples of variable declarations:
12.
Count, Sum : Integer;
Size : Integer range 0 ┬╖┬╖ 10_000 := 0;
Sorted : Boolean := False;
Color_Table : array(1 ┬╖┬╖ Max) of Color;
Option : Bit_Vector(1 ┬╖┬╖ 10) := (others => True);
Hello : constant String := "Hi, world.";
13. Examples of constant declarations:
14.
Limit : constant Integer := 10_000;
Low_Limit : constant Integer := Limit/10;
Tolerance : constant Real := Dispersion(1.15);
ΓòÉΓòÉΓòÉ 6.3.2. Number Declarations ΓòÉΓòÉΓòÉ
1. A number_declaration declares a named number.
Syntax
2.
number_declaration ::=
defining_identifier_list : constant := static_expression;
Name Resolution Rules
3. The static_expression given for a number_declaration is expected to be of
any numeric type.
Legality Rules
4. The static_expression given for a number declaration shall be a static
expression, as defined by clause (see 4.9).
Static Semantics
5. The named number denotes a value of type universal_integer if the type of
the static_expression is an integer type. The named number denotes a
value of type universal_real if the type of the static_expression is a
real type.
6. The value denoted by the named number is the value of the
static_expression, converted to the corresponding universal type.
Dynamic Semantics
7. The elaboration of a number_declaration has no effect.
Examples
8. Examples of number declarations:
9.
Two_Pi : constant := 2.0*Ada.Numerics.Pi;
-- a real number, see A.5
10.
Max : constant := 500; -- an integer number
Max_Line_Size : constant := Max/6; -- the integer 83
Power_16 : constant := 2**16; -- the integer 65_536
One, Un, Eins : constant := 1; -- three different names for 1
ΓòÉΓòÉΓòÉ 6.4. Derived Types and Classes ΓòÉΓòÉΓòÉ
1. A derived_type_definition defines a new type (and its first subtype)
whose characteristics are derived from those of a parent type.
Syntax
2.
derived_type_definition ::= [abstract] new
parent_subtype_indication [record_extension_part]
Legality Rules
3. The parent_subtype_indication defines the parent subtype; its type is the
parent type.
4. A type shall be completely defined, see 3.11.1, prior to being specified
as the parent type in a derived_type_definition -- the
full_type_declarations for the parent type and any of its subcomponents
have to precede the derived_type_definition.
5. If there is a record_extension_part, the derived type is called a record
extension of the parent type. A record_extension_part shall be provided
if and only if the parent type is a tagged type.
Static Semantics
6. The first subtype of the derived type is unconstrained if a
known_discriminant_part is provided in the declaration of the derived
type, or if the parent subtype is unconstrained. Otherwise, the
constraint of the first subtype corresponds to that of the parent subtype
in the following sense: it is the same as that of the parent subtype
except that for a range constraint (implicit or explicit), the value of
each bound of its range is replaced by the corresponding value of the
derived type.
7. The characteristics of the derived type are defined as follows:
a. Each class of types that includes the parent type also includes the
derived type.
b. If the parent type is an elementary type or an array type, then the
set of possible values of the derived type is a copy of the set of
possible values of the parent type. For a scalar type, the base
range of the derived type is the same as that of the parent type.
c. If the parent type is a composite type other than an array type,
then the components, protected subprograms, and entries that are
declared for the derived type are as follows:
1. The discriminants specified by a new known_discriminant_part,
if there is one; otherwise, each discriminant of the parent
type (implicitly declared in the same order with the same
specifications) -- in the latter case, the discriminants are
said to be inherited, or if unknown in the parent, are also
unknown in the derived type;
2. Each nondiscriminant component, entry, and protected subprogram
of the parent type, implicitly declared in the same order with
the same declarations; these components, entries, and protected
subprograms are said to be inherited;
3. Each component declared in a record_extension_part, if any.
a. Declarations of components, protected subprograms, and entries,
whether implicit or explicit, occur immediately within the
declarative region of the type, in the order indicated above,
following the parent subtype_indication.
b. The derived type is limited if and only if the parent type is
limited.
c. For each predefined operator of the parent type, there is a
corresponding predefined operator of the derived type.
d. For each user-defined primitive subprogram (other than a
user-defined equality operator -- see below) of the parent type that
already exists at the place of the derived_type_definition, there
exists a corresponding inherited primitive subprogram of the derived
type with the same defining name. Primitive user-defined equality
operators of the parent type are also inherited by the derived type,
except when the derived type is a nonlimited record extension, and
the inherited operator would have a profile that is type conformant
with the profile of the corresponding predefined equality operator;
in this case, the user-defined equality operator is not inherited,
but is rather incorporated into the implementation of the predefined
equality operator of the record extension, see 4.5.2.
e. The profile of an inherited subprogram (including an inherited
enumeration literal) is obtained from the profile of the
corresponding (user-defined) primitive subprogram of the parent
type, after systematic replacement of each subtype of its profile,
see 6.1, that is of the parent type with a corresponding subtype of
the derived type. For a given subtype of the parent type, the
corresponding subtype of the derived type is defined as follows:
1. If the declaration of the derived type has neither a
known_discriminant_part nor a record_extension_part, then the
corresponding subtype has a constraint that corresponds (as
defined above for the first subtype of the derived type) to
that of the given subtype.
2. If the derived type is a record extension, then the
corresponding subtype is the first subtype of the derived type.
3. If the derived type has a new known_discriminant_part but is
not a record extension, then the corresponding subtype is
constrained to those values that when converted to the parent
type belong to the given subtype, see 4.6.
a. The same formal parameters have default_expressions in the profile
of the inherited subprogram. Any type mismatch due to the systematic
replacement of the parent type by the derived type is handled as
part of the normal type conversion associated with parameter passing
-- see 6.4.1.
1. If a primitive subprogram of the parent type is visible at the place of
the derived_type_definition, then the corresponding inherited subprogram
is implicitly declared immediately after the derived_type_definition.
Otherwise, the inherited subprogram is implicitly declared later or not
at all, as explained in 7.3.1.
2. A derived type can also be defined by a private_extension_declaration
(see 7.3) or a formal_derived_type_definition, see 12.5.1. Such a derived
type is a partial view of the corresponding full or actual type.
3. All numeric types are derived types, in that they are implicitly derived
from a corresponding root numeric type (see 3.5.4, and 3.5.6).
Dynamic Semantics
4. The elaboration of a derived_type_definition creates the derived type and
its first subtype, and consists of the elaboration of the
subtype_indication and the record_extension_part, if any. If the
subtype_indication depends on a discriminant, then only those expressions
that do not depend on a discriminant are evaluated.
5. For the execution of a call on an inherited subprogram, a call on the
corresponding primitive subprogram of the parent type is performed; the
normal conversion of each actual parameter to the subtype of the
corresponding formal parameter, see 6.4.1 performs any necessary type
conversion as well. If the result type of the inherited subprogram is the
derived type, the result of calling the parent's subprogram is converted
to the derived type.
NOTES
6. (10) Classes are closed under derivation -- any class that contains a
type also contains its derivatives. Operations available for a given
class of types are available for the derived types in that class.
7. (11) Evaluating an inherited enumeration literal is equivalent to
evaluating the corresponding enumeration literal of the parent type, and
then converting the result to the derived type. This follows from their
equivalence to parameterless functions.
8. (12) A generic subprogram is not a subprogram, and hence cannot be a
primitive subprogram and cannot be inherited by a derived type. On the
other hand, an instance of a generic subprogram can be a primitive
subprogram, and hence can be inherited.
9. (13) If the parent type is an access type, then the parent and the
derived type share the same storage pool; there is a null access value
for the derived type and it is the implicit initial value for the type
(see 3.10).
10. (14) If the parent type is a boolean type, the predefined relational
operators of the derived type deliver a result of the predefined type
Boolean, see 4.5.2. If the parent type is an integer type, the right
operand of the predefined exponentiation operator is of the predefined
type Integer, see 4.5.6.
11. (15) Any discriminants of the parent type are either all inherited, or
completely replaced with a new set of discriminants.
12. (16) For an inherited subprogram, the subtype of a formal parameter of
the derived type need not have any value in common with the first subtype
of the derived type.
13. (17) If the reserved word abstract is given in the declaration of a type,
the type is abstract, see 3.9.3.
Examples
14. Examples of derived type declarations:
15.
type Local_Coordinate is new Coordinate; -- two different types
type Midweek is new Day range Tue ┬╖┬╖ Thu; -- see 3.5.1
type Counter is new Positive; -- same range as Positive
16.
type Special_Key is new Key_Manager.Key; -- see 7.3.1
-- the inherited subprograms have the following specifications:
-- procedure Get_Key(K : out Special_Key);
-- function "<"(X,Y : Special_Key) return Boolean;
3.4.1 Derivation Classes
ΓòÉΓòÉΓòÉ 6.4.1. Derivation Classes ΓòÉΓòÉΓòÉ
1. In addition to the various language-defined classes of types, types can
be grouped into derivation classes.
Static Semantics
2. A derived type is derived from its parent type directly; it is derived
indirectly from any type from which its parent type is derived. The
derivation class of types for a type T (also called the class rooted at
T) is the set consisting of T (the root type of the class) and all types
derived from T (directly or indirectly) plus any associated universal or
class-wide types (defined below).
3. Every type is either a specific type, a class-wide type, or a universal
type. A specific type is one defined by a type_declaration, a
formal_type_declaration, or a full type definition embedded in a
declaration for an object. Class-wide and universal types are implicitly
defined, to act as representatives for an entire class of types, as
follows:
4. Class-wide types Class-wide types are defined for (and belong to) each
derivation class rooted at a tagged type, see 3.9. Given a subtype S of a
tagged type T, S'Class is the subtype_mark for a corresponding subtype of
the tagged class-wide type T'Class. Such types are called ``class-wide''
because when a formal parameter is defined to be of a class-wide type
T'Class, an actual parameter of any type in the derivation class rooted
at T is acceptable, see 8.6.
a. The set of values for a class-wide type T'Class is the discriminated
union of the set of values of each specific type in the derivation
class rooted at T (the tag acts as the implicit discriminant -- see
3.9.). Class-wide types have no primitive subprograms of their own.
However, as explained in 3.9.2, operands of a class-wide type
T'Class can be used as part of a dispatching call on a primitive
subprogram of the type T. The only components (including
discriminants) of T'Class that are visible are those of T. If S is a
first subtype, then S'Class is a first subtype.
1. Universal types Universal types are defined for (and belong to) the
integer, real, and fixed point classes, and are referred to in this
standard as respectively, universal_integer, universal_real, and
universal_fixed. These are analogous to class-wide types for these
language-defined numeric classes. As with class-wide types, if a formal
parameter is of a universal type, then an actual parameter of any type in
the corresponding class is acceptable. In addition, a value of a
universal type (including an integer or real numeric_literal) is
``universal'' in that it is acceptable where some particular type in the
class is expected, see 8.6.
a. The set of values of a universal type is the undiscriminated union
of the set of values possible for any definable type in the
associated class. Like class-wide types, universal types have no
primitive subprograms of their own. However, their ``universality''
allows them to be used as operands with the primitive subprograms of
any type in the corresponding class.
1. The integer and real numeric classes each have a specific root type in
addition to their universal type, named respectively root_integer and
root_real.
2. A class-wide or universal type is said to cover all of the types in its
class. A specific type covers only itself.
3. A specific type T2 is defined to be a descendant of a type T1 if T2 is
the same as T1, or if T2 is derived (directly or indirectly) from T1. A
class-wide type T2'Class is defined to be a descendant of type T1 if T2
is a descendant of T1. Similarly, the universal types are defined to be
descendants of the root types of their classes. If a type T2 is a
descendant of a type T1, then T1 is called an ancestor of T2. The
ultimate ancestor of a type is the ancestor of the type that is not a
descendant of any other type.
4. An inherited component (including an inherited discriminant) of a derived
type is inherited from a given ancestor of the type if the corresponding
component was inherited by each derived type in the chain of derivations
going back to the given ancestor.
NOTES
5. (18) Because operands of a universal type are acceptable to the
predefined operators of any type in their class, ambiguity can result.
For universal_integer and universal_real, this potential ambiguity is
resolved by giving a preference, see 8.6 to the predefined operators of
the corresponding root types (root_integer and root_real, respectively).
Hence, in an apparently ambiguous expression like
6.
1 + 4 < 7
7. where each of the literals is of type universal_integer, the predefined
operators of root_integer will be preferred over those of other specific
integer types, thereby resolving the ambiguity.
ΓòÉΓòÉΓòÉ 6.5. Scalar Types ΓòÉΓòÉΓòÉ
1. Scalar types comprise enumeration types, integer types, and real types.
Enumeration types and integer types are called discrete types; each value
of a discrete type has a position number which is an integer value.
Integer types and real types are called numeric types. All scalar types
are ordered, that is, all relational operators are predefined for their
values.
Syntax
2.
range_constraint ::= range range
3.
range ::=
range_attribute_reference
| simple_expression ┬╖┬╖ simple_expression
4. A range has a lower bound and an upper bound and specifies a subset of
the values of some scalar type (the type of the range). A range with
lower bound L and upper bound R is described by ``L ┬╖┬╖ R''. If R is less
than L, then the range is a null range, and specifies an empty set of
values. Otherwise, the range specifies the values of the type from the
lower bound to the upper bound, inclusive. A value belongs to a range if
it is of the type of the range, and is in the subset of values specified
by the range. A value satisfies a range constraint if it belongs to the
associated range. One range is included in another if all values that
belong to the first range also belong to the second.
Name Resolution Rules
5. For a subtype_indication containing a range_constraint, either directly
or as part of some other scalar_constraint, the type of the range shall
resolve to that of the type determined by the subtype_mark of the
subtype_indication. For a range of a given type, the simple_expressions
of the range (likewise, the simple_expressions of the equivalent range
for a range_attribute_reference) are expected to be of the type of the
range.
Static Semantics
6. The base range of a scalar type is the range of finite values of the type
that can be represented in every unconstrained object of the type; it is
also the range supported at a minimum for intermediate values during the
evaluation of expressions involving predefined operators of the type.
7. A constrained scalar subtype is one to which a range constraint applies.
The range of a constrained scalar subtype is the range associated with
the range constraint of the subtype. The range of an unconstrained scalar
subtype is the base range of its type.
Dynamic Semantics
8. A range is compatible with a scalar subtype if and only if it is either a
null range or each bound of the range belongs to the range of the
subtype. A range_constraint is compatible with a scalar subtype if and
only if its range is compatible with the subtype.
9. The elaboration of a range_constraint consists of the evaluation of the
range. The evaluation of a range determines a lower bound and an upper
bound. If simple_expressions are given to specify bounds, the evaluation
of the range evaluates these simple_expressions in an arbitrary order,
and converts them to the type of the range. If a
range_attribute_reference is given, the evaluation of the range consists
of the evaluation of the range_attribute_reference.
10. Attributes
11. For every scalar subtype S, the following attributes are defined:
12. S'First
S'First denotes the lower bound of the range of S. The value
of this attribute is of the type of S.
13. S'Last
S'Last denotes the upper bound of the range of S. The value
of this attribute is of the type of S.
14. S'Range
S'Range is equivalent to the range S'First ┬╖┬╖ S'Last.
15. S'Base
S'Base denotes an unconstrained subtype of the type of
S. This unconstrained subtype is called the base subtype of
the type.
16. S'Min S'Min denotes a function with the following specification:
a.
function S'Min(Left, Right : S'Base)
return S'Base
b. The function returns the lesser of the values of the two parameters.
1. S'Max S'Max denotes a function with the following specification:
a.
function S'Max(Left, Right : S'Base)
return S'Base
b. The function returns the greater of the values of the two
parameters.
1. S'Succ S'Succ denotes a function with the following specification:
a.
function S'Succ(Arg : S'Base)
return S'Base
b. For an enumeration type, the function returns the value whose
position number is one more than that of the value of Arg;
Constraint_Error is raised if there is no such value of the type.
For an integer type, the function returns the result of adding one
to the value of Arg. For a fixed point type, the function returns
the result of adding small to the value of Arg. For a floating point
type, the function returns the machine number (as defined in 3.5.7.)
immediately above the value of Arg; Constraint_Error is raised if
there is no such machine number.
1. S'Pred S'Pred denotes a function with the following specification:
a.
function S'Pred(Arg : S'Base)
return S'Base
b. For an enumeration type, the function returns the value whose
position number is one less than that of the value of Arg;
Constraint_Error is raised if there is no such value of the type.
For an integer type, the function returns the result of subtracting
one from the value of Arg. For a fixed point type, the function
returns the result of subtracting small from the value of Arg. For a
floating point type, the function returns the machine number (as
defined in 3.5.7.) immediately below the value of Arg;
Constraint_Error is raised if there is no such machine number.
1. S'Wide_Image S'Wide_Image denotes a function with the following
specification:
a.
function S'Wide_Image(Arg : S'Base)
return Wide_String
b. The function returns an image of the value of Arg, that is, a
sequence of characters representing the value in display form. The
lower bound of the result is one.
c. The image of an integer value is the corresponding decimal literal,
without underlines, leading zeros, exponent, or trailing spaces, but
with a single leading character that is either a minus sign or a
space.
d. The image of an enumeration value is either the corresponding
identifier in upper case or the corresponding character literal
(including the two apostrophes); neither leading nor trailing spaces
are included. For a nongraphic character (a value of a character
type that has no enumeration literal associated with it), the result
is a corresponding language-defined or implementation-defined name
in upper case (for example, the image of the nongraphic character
identified as nul is ``NUL'' -- the quotes are not part of the
image).
e. The image of a floating point value is a decimal real literal best
approximating the value (rounded away from zero if halfway between)
with a single leading character that is either a minus sign or a
space, a single digit (that is nonzero unless the value is zero), a
decimal point, S'Digits-1, see 3.5.8, digits after the decimal point
(but one if S'Digits is one), an upper case E, the sign of the
exponent (either + or -), and two or more digits (with leading zeros
if necessary) representing the exponent. If S'Signed_Zeros is True,
then the leading character is a minus sign for a negatively signed
zero.
f. The image of a fixed point value is a decimal real literal best
approximating the value (rounded away from zero if halfway between)
with a single leading character that is either a minus sign or a
space, one or more digits before the decimal point (with no
redundant leading zeros), a decimal point, and S'Aft, see 3.5.10,
digits after the decimal point.
1. S'Image S'Image denotes a function with the following specification:
a.
function S'Image(Arg : S'Base)
return String
b. The function returns an image of the value of Arg as a String. The
lower bound of the result is one. The image has the same sequence of
graphic characters as that defined for S'Wide_Image if all the
graphic characters are defined in Character; otherwise the sequence
of characters is implementation defined (but no shorter than that of
S'Wide_Image for the same value of Arg).
1. S'Wide_Width
S'Wide_Width denotes the maximum length of a Wide_String
returned by S'Wide_Image over all values of the subtype S. It
denotes zero for a subtype that has a null range. Its type
is universal_integer.
2. S'Width
S'Width denotes the maximum length of a String returned by
S'Image over all values of the subtype S. It denotes
zero for a subtype that has a null range. Its type is
universal_integer.
3. S'Wide_Value S'Wide_Value denotes a function with the following
specification:
a.
function S'Wide_Value(Arg : Wide_String)
return S'Base
b. This function returns a value given an image of the value as a
Wide_String, ignoring any leading or trailing spaces.
c. For the evaluation of a call on S'Wide_Value for an enumeration
subtype S, if the sequence of characters of the parameter (ignoring
leading and trailing spaces) has the syntax of an enumeration
literal and if it corresponds to a literal of the type of S (or
corresponds to the result of S'Wide_Image for a nongraphic character
of the type), the result is the corresponding enumeration value;
otherwise Constraint_Error is raised.
d. For the evaluation of a call on S'Wide_Value (or S'Value) for an
integer subtype S, if the sequence of characters of the parameter
(ignoring leading and trailing spaces) has the syntax of an integer
literal, with an optional leading sign character (plus or minus for
a signed type; only plus for a modular type), and the corresponding
numeric value belongs to the base range of the type of S, then that
value is the result; otherwise Constraint_Error is raised.
e. For the evaluation of a call on S'Wide_Value (or S'Value) for a real
subtype S, if the sequence of characters of the parameter (ignoring
leading and trailing spaces) has the syntax of one of the following:
1. numeric_literal
2. numeral.[exponent]
3. ┬╖numeral[exponent]
4. base#based_numeral.#[exponent]
5. base#.based_numeral#[exponent]
a. with an optional leading sign character (plus or minus), and if the
corresponding numeric value belongs to the base range of the type of
S, then that value is the result; otherwise Constraint_Error is
raised. The sign of a zero value is preserved (positive if none has
been specified) if S'Signed_Zeros is True.
1. S'Value S'Value denotes a function with the following specification:
a.
function S'Value(Arg : String)
return S'Base
b. This function returns a value given an image of the value as a
String, ignoring any leading or trailing spaces.
c. For the evaluation of a call on S'Value for an enumeration subtype
S, if the sequence of characters of the parameter (ignoring leading
and trailing spaces) has the syntax of an enumeration literal and if
it corresponds to a literal of the type of S (or corresponds to the
result of S'Image for a value of the type), the result is the
corresponding enumeration value; otherwise Constraint_Error is
raised. For a numeric subtype S, the evaluation of a call on S'Value
with Arg of type String is equivalent to a call on S'Wide_Value for
a corresponding Arg of type Wide_String.
Implementation Permissions
1. An implementation may extend the Wide_Value, Value, Wide_Image, and Image
attributes of a floating point type to support special values such as
infinities and NaNs.
NOTES
2. (19) The evaluation of S'First or S'Last never raises an exception. If a
scalar subtype S has a nonnull range, S'First and S'Last belong to this
range. These values can, for example, always be assigned to a variable of
subtype S.
3. (20) For a subtype of a scalar type, the result delivered by the
attributes Succ, Pred, and Value might not belong to the subtype;
similarly, the actual parameters of the attributes Succ, Pred, and Image
need not belong to the subtype.
4. (21) For any value V (including any nongraphic character) of an
enumeration subtype S, S'Value(S'Image(V)) equals V, as does
S'Wide_Value(S'Wide_Image(V)). Neither expression ever raises
Constraint_Error.
Examples
5. Examples of ranges:
6.
-10 ┬╖┬╖ 10
X ┬╖┬╖ X + 1
0.0 ┬╖┬╖ 2.0*Pi
Red ┬╖┬╖ Green -- see 3.5.1
1 ┬╖┬╖ 0 -- a null range
Table'Range -- a range attribute reference, see 3.6
7. Examples of range constraints:
8.
range -999.0 ┬╖┬╖ +999.0
range S'First+1 ┬╖┬╖ S'Last-1
3.5.1 Enumeration Types
3.5.2 Character Types
3.5.3 Boolean Types
3.5.4 Integer Types
3.5.5 Operations of Discrete Types
3.5.6 Real Types
3.5.7 Floating Point Types
3.5.8 Operations of Floating Point Types
3.5.9 Fixed Point Types
3.5.10 Operations of Fixed Point Types
ΓòÉΓòÉΓòÉ 6.5.1. Enumeration Types ΓòÉΓòÉΓòÉ
1. An enumeration_type_definition defines an enumeration type.
Syntax
2.
enumeration_type_definition ::=
(enumeration_literal_specification
{, enumeration_literal_specification})
3.
enumeration_literal_specification ::=
defining_identifier | defining_character_literal
4.
defining_character_literal ::= character_literal
Legality Rules
5. The defining_identifiers and defining_character_literals listed in an
enumeration_type_definition shall be distinct.
Static Semantics
6. Each enumeration_literal_specification is the explicit declaration of the
corresponding enumeration literal: it declares a parameterless function,
whose defining name is the defining_identifier or
defining_character_literal, and whose result type is the enumeration
type.
7. Each enumeration literal corresponds to a distinct value of the
enumeration type, and to a distinct position number. The position number
of the value of the first listed enumeration literal is zero; the
position number of the value of each subsequent enumeration literal is
one more than that of its predecessor in the list.
8. The predefined order relations between values of the enumeration type
follow the order of corresponding position numbers.
9. If the same defining_identifier or defining_character_literal is
specified in more than one enumeration_type_definition, the corresponding
enumeration literals are said to be overloaded. At any place where an
overloaded enumeration literal occurs in the text of a program, the type
of the enumeration literal has to be determinable from the context, see
8.6.
Dynamic Semantics
10. The elaboration of an enumeration_type_definition creates the enumeration
type and its first subtype, which is constrained to the base range of the
type.
11. When called, the parameterless function associated with an enumeration
literal returns the corresponding value of the enumeration type.
NOTES
12. (22) If an enumeration literal occurs in a context that does not
otherwise suffice to determine the type of the literal, then
qualification by the name of the enumeration type is one way to resolve
the ambiguity, see 4.7.
Examples
13. Examples of enumeration types and subtypes:
14.
type Day is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);
type Suit is (Clubs, Diamonds, Hearts, Spades);
type Gender is (M, F);
type Level is (Low, Medium, Urgent);
type Color is (White, Red, Yellow, Green, Blue, Brown, Black);
type Light is (Red, Amber, Green); -- Red and Green are overloaded
15.
type Hexa is ('A', 'B', 'C', 'D', 'E', 'F');
type Mixed is ('A', 'B', '*', B, None, '?', '%');
16.
subtype Weekday is Day range Mon ┬╖┬╖ Fri;
subtype Major is Suit range Hearts ┬╖┬╖ Spades;
subtype Rainbow is Color range Red ┬╖┬╖ Blue;
-- the Color Red, not the Light
ΓòÉΓòÉΓòÉ 6.5.2. Character Types ΓòÉΓòÉΓòÉ
Static Semantics
1. An enumeration type is said to be a character type if at least one of its
enumeration literals is a character_literal.
2. The predefined type Character is a character type whose values correspond
to the 256 code positions of Row 00 (also known as Latin-1) of the ISO
10646 Basic Multilingual Plane (BMP). Each of the graphic characters of
Row 00 of the BMP has a corresponding character_literal in Character.
Each of the nongraphic positions of Row 00 (0000-001F and 007F-009F) has
a corresponding language-defined name, which is not usable as an
enumeration literal, but which is usable with the attributes (Wide_)Image
and (Wide_)Value; these names are given in the definition of type
Character in A.1: ``The Package Standard'', but are set in italics.
3. The predefined type Wide_Character is a character type whose values
correspond to the 65536 code positions of the ISO 10646 Basic
Multilingual Plane (BMP). Each of the graphic characters of the BMP has a
corresponding character_literal in Wide_Character. The first 256 values
of Wide_Character have the same character_literal or language-defined
name as defined for Character. The last 2 values of Wide_Character
correspond to the nongraphic positions FFFE and FFFF of the BMP, and are
assigned the language-defined names FFFE and FFFF. As with the other
language-defined names for nongraphic characters, the names FFFE and FFFF
are usable only with the attributes (Wide_)Image and (Wide_)Value; they
are not usable as enumeration literals. All other values of
Wide_Character are considered graphic characters, and have a
corresponding character_literal.
Implementation Permissions
4. In a nonstandard mode, an implementation may provide other
interpretations for the predefined types Character and Wide_Character, to
conform to local conventions.
Implementation Advice
5. If an implementation supports a mode with alternative interpretations for
Character and Wide_Character, the set of graphic characters of Character
should nevertheless remain a proper subset of the set of graphic
characters of Wide_Character. Any character set ``localizations'' should
be reflected in the results of the subprograms defined in the
language-defined package Characters.Handling, see A.3, available in such
a mode. In a mode with an alternative interpretation of Character, the
implementation should also support a corresponding change in what is a
legal identifier_letter.
NOTES
6. (23) The language-defined library package Characters.Latin_1 (A.3.3)
includes the declaration of constants denoting control characters, lower
case characters, and special characters of the predefined type Character.
7. (24) A conventional character set such as EBCDIC can be declared as a
character type; the internal codes of the characters can be specified by
an enumeration_representation_clause as explained in clause (see 13.4).
Examples
8. Example of a character type:
9.
type Roman_Digit is ('I', 'V', 'X', 'L', 'C', 'D', 'M');
ΓòÉΓòÉΓòÉ 6.5.3. Boolean Types ΓòÉΓòÉΓòÉ
Static Semantics
1. There is a predefined enumeration type named Boolean, declared in the
visible part of package Standard. It has the two enumeration literals
False and True ordered with the relation False < True. Any descendant of
the predefined type Boolean is called a boolean type.
ΓòÉΓòÉΓòÉ 6.5.4. Integer Types ΓòÉΓòÉΓòÉ
1. An integer_type_definition defines an integer type; it defines either a
signed integer type, or a modular integer type. The base range of a
signed integer type includes at least the values of the specified range.
A modular type is an integer type with all arithmetic modulo a specified
positive modulus; such a type corresponds to an unsigned type with
wrap-around semantics.
Syntax
2.
integer_type_definition ::=
signed_integer_type_definition | modular_type_definition
3.
signed_integer_type_definition ::=
range static_simple_expression ┬╖┬╖ static_simple_expression
4.
modular_type_definition ::= mod static_expression
Name Resolution Rules
5. Each simple_expression in a signed_integer_type_definition is expected to
be of any integer type; they need not be of the same type. The expression
in a modular_type_definition is likewise expected to be of any integer
type.
Legality Rules
6. The simple_expressions of a signed_integer_type_definition shall be
static, and their values shall be in the range System.Min_Int ┬╖┬╖
System.Max_Int.
7. The expression of a modular_type_definition shall be static, and its
value (the modulus) shall be positive, and shall be no greater than
System.Max_Binary_Modulus if a power of 2, or no greater than
System.Max_Nonbinary_Modulus if not.
Static Semantics
8. The set of values for a signed integer type is the (infinite) set of
mathematical integers, though only values of the base range of the type
are fully supported for run-time operations. The set of values for a
modular integer type are the values from 0 to one less than the modulus,
inclusive.
9. A signed_integer_type_definition defines an integer type whose base range
includes at least the values of the simple_expressions and is symmetric
about zero, excepting possibly an extra negative value. A
signed_integer_type_definition also defines a constrained first subtype
of the type, with a range whose bounds are given by the values of the
simple_expressions, converted to the type being defined.
10. A modular_type_definition defines a modular type whose base range is from
zero to one less than the given modulus. A modular_type_definition also
defines a constrained first subtype of the type with a range that is the
same as the base range of the type.
11. There is a predefined signed integer subtype named Integer, declared in
the visible part of package Standard. It is constrained to the base range
of its type.
12. Integer has two predefined subtypes, declared in the visible part of
package Standard:
13.
subtype Natural is Integer range 0 ┬╖┬╖ Integer'Last;
subtype Positive is Integer range 1 ┬╖┬╖ Integer'Last;
14. A type defined by an integer_type_definition is implicitly derived from
root_integer, an anonymous predefined (specific) integer type, whose base
range is System.Min_Int ┬╖┬╖ System.Max_Int. However, the base range of the
new type is not inherited from root_integer, but is instead determined by
the range or modulus specified by the integer_type_definition. Integer
literals are all of the type universal_integer, the universal type, see
3.4.1, for the class rooted at root_integer, allowing their use with the
operations of any integer type.
15. The position number of an integer value is equal to the value.
16. For every modular subtype S, the following attribute is defined:
17. S'Modulus
S'Modulus yields the modulus of the type of S, as a value of
the type universal_integer.
Dynamic Semantics
18. The elaboration of an integer_type_definition creates the integer type
and its first subtype.
19. For a modular type, if the result of the execution of a predefined
operator, see 4.5 is outside the base range of the type, the result is
reduced modulo the modulus of the type to a value that is within the base
range of the type.
20. For a signed integer type, the exception Constraint_Error is raised by
the execution of an operation that cannot deliver the correct result
because it is outside the base range of the type. For any integer type,
Constraint_Error is raised by the operators "/", "rem", and "mod" if the
right operand is zero.
Implementation Requirements
21. In an implementation, the range of Integer shall include the range
-2**15+1 ┬╖┬╖ +2**15-1.
22. If Long_Integer is predefined for an implementation, then its range shall
include the range -2**31+1 ┬╖┬╖ +2**31-1.
23. System.Max_Binary_Modulus shall be at least 2**16.
Implementation Permissions
24. For the execution of a predefined operation of a signed integer type, the
implementation need not raise Constraint_Error if the result is outside
the base range of the type, so long as the correct result is produced.
25. An implementation may provide additional predefined signed integer types,
declared in the visible part of Standard, whose first subtypes have names
of the form Short_Integer, Long_Integer, Short_Short_Integer,
Long_Long_Integer, etc. Different predefined integer types are allowed to
have the same base range. However, the range of Integer should be no
wider than that of Long_Integer. Similarly, the range of Short_Integer
(if provided) should be no wider than Integer. Corresponding
recommendations apply to any other predefined integer types. There need
not be a named integer type corresponding to each distinct base range
supported by an implementation. The range of each first subtype should be
the base range of its type.
26. An implementation may provide nonstandard integer types, descendants of
root_integer that are declared outside of the specification of package
Standard, which need not have all the standard characteristics of a type
defined by an integer_type_definition. For example, a nonstandard integer
type might have an asymmetric base range or it might not be allowed as an
array or loop index (a very long integer). Any type descended from a
nonstandard integer type is also nonstandard. An implementation may place
arbitrary restrictions on the use of such types; it is implementation
defined whether operators that are predefined for ``any integer type''
are defined for a particular nonstandard integer type. In any case, such
types are not permitted as explicit_generic_actual_parameters for formal
scalar types -- see 12.5.2.
27. For a one's complement machine, the high bound of the base range of a
modular type whose modulus is one less than a power of 2 may be equal to
the modulus, rather than one less than the modulus. It is implementation
defined for which powers of 2, if any, this permission is exercised.
Implementation Advice
28. An implementation should support Long_Integer in addition to Integer if
the target machine supports 32-bit (or longer) arithmetic. No other named
integer subtypes are recommended for package Standard. Instead,
appropriate named integer subtypes should be provided in the library
package Interfaces, see B.2.
29. An implementation for a two's complement machine should support modular
types with a binary modulus up to System.Max_Int*2+2. An implementation
should support a nonbinary modulus up to Integer'Last.
NOTES
30. (25) Integer literals are of the anonymous predefined integer type
universal_integer. Other integer types have no literals. However, the
overload resolution rules, see 8.6: ``The Context of Overload
Resolution'', allow expressions of the type universal_integer whenever an
integer type is expected.
31. (26) The same arithmetic operators are predefined for all signed integer
types defined by a signed_integer_type_definition, see 4.5: ``Operators
and Expression Evaluation''. For modular types, these same operators are
predefined, plus bit-wise logical operators (and, or, xor, and not). In
addition, for the unsigned types declared in the language-defined package
Interfaces, see B.2, functions are defined that provide bit-wise shifting
and rotating.
32. (27) Modular types match a generic_formal_parameter_declaration of the
form "type T is mod <>;"; signed integer types match "type T is range
<>;", see 12.5.2.
Examples
33. Examples of integer types and subtypes:
34.
type Page_Num is range 1 ┬╖┬╖ 2_000;
type Line_Size is range 1 ┬╖┬╖ Max_Line_Size;
35.
subtype Small_Int is Integer range -10 ┬╖┬╖ 10;
subtype Column_Ptr is Line_Size range 1 ┬╖┬╖ 10;
subtype Buffer_Size is Integer range 0 ┬╖┬╖ Max;
36.
type Byte is mod 256; -- an unsigned byte
type Hash_Index is mod 97; -- modulus is prime
ΓòÉΓòÉΓòÉ 6.5.5. Operations of Discrete Types ΓòÉΓòÉΓòÉ
Static Semantics
1. For every discrete subtype S, the following attributes are defined:
2. S'Pos S'Pos denotes a function with the following specification:
a.
function S'Pos(Arg : S'Base)
return universal_integer
b. This function returns the position number of the value of Arg, as a
value of type universal_integer.
1. S'Val S'Val denotes a function with the following specification:
a.
function S'Val(Arg : universal_integer)
return S'Base
b. This function returns a value of the type of S whose position number
equals the value of Arg. For the evaluation of a call on S'Val, if
there is no value in the base range of its type with the given
position number, Constraint_Error is raised.
Implementation Advice
1. For the evaluation of a call on S'Pos for an enumeration subtype, if the
value of the operand does not correspond to the internal code for any
enumeration literal of its type (perhaps due to an uninitialized
variable), then the implementation should raise Program_Error. This is
particularly important for enumeration types with noncontiguous internal
codes specified by an enumeration_representation_clause.
NOTES
2. (28) Indexing and loop iteration use values of discrete types.
3. (29) The predefined operations of a discrete type include the assignment
operation, qualification, the membership tests, and the relational
operators; for a boolean type they include the short-circuit control
forms and the logical operators; for an integer type they include type
conversion to and from other numeric types, as well as the binary and
unary adding operators - and +, the multiplying operators, the unary
operator abs, and the exponentiation operator. The assignment operation
is described in 5.2. The other predefined operations are described in
Section 4.
4. (30) As for all types, objects of a discrete type have Size and Address
attributes, see 13.3.
5. (31) For a subtype of a discrete type, the result delivered by the
attribute Val might not belong to the subtype; similarly, the actual
parameter of the attribute Pos need not belong to the subtype. The
following relations are satisfied (in the absence of an exception) by
these attributes:
6.
S'Val(S'Pos(X)) = X
S'Pos(S'Val(N)) = N
Examples
7. Examples of attributes of discrete subtypes:
8.
-- For the types and subtypes declared in subclause
-- see 3.5.1, the following hold:
9.
-- Color'First = White, Color'Last = Black
-- Rainbow'First = Red, Rainbow'Last = Blue
10.
-- Color'Succ(Blue) = Rainbow'Succ(Blue) = Brown
-- Color'Pos(Blue) = Rainbow'Pos(Blue) = 4
-- Color'Val(0) = Rainbow'Val(0) = White
ΓòÉΓòÉΓòÉ 6.5.6. Real Types ΓòÉΓòÉΓòÉ
1. Real types provide approximations to the real numbers, with relative
bounds on errors for floating point types, and with absolute bounds for
fixed point types.
Syntax
2.
real_type_definition ::=
floating_point_definition | fixed_point_definition
Static Semantics
3. A type defined by a real_type_definition is implicitly derived from
root_real, an anonymous predefined (specific) real type. Hence, all real
types, whether floating point or fixed point, are in the derivation class
rooted at root_real.
4. Real literals are all of the type universal_real, the universal type (see
3.4.1) for the class rooted at root_real, allowing their use with the
operations of any real type. Certain multiplying operators have a result
type of universal_fixed, see 4.5.5, the universal type for the class of
fixed point types, allowing the result of the multiplication or division
to be used where any specific fixed point type is expected.
Dynamic Semantics
5. The elaboration of a real_type_definition consists of the elaboration of
the floating_point_definition or the fixed_point_definition.
Implementation Requirements
6. An implementation shall perform the run-time evaluation of a use of a
predefined operator of root_real with an accuracy at least as great as
that of any floating point type definable by a floating_point_definition.
Implementation Permissions
7. For the execution of a predefined operation of a real type, the
implementation need not raise Constraint_Error if the result is outside
the base range of the type, so long as the correct result is produced, or
the Machine_Overflows attribute of the type is false, see G.2.
8. An implementation may provide nonstandard real types, descendants of
root_real that are declared outside of the specification of package
Standard, which need not have all the standard characteristics of a type
defined by a real_type_definition. For example, a nonstandard real type
might have an asymmetric or unsigned base range, or its predefined
operations might wrap around or ``saturate'' rather than overflow
(modular or saturating arithmetic), or it might not conform to the
accuracy model, see G.2. Any type descended from a nonstandard real type
is also nonstandard. An implementation may place arbitrary restrictions
on the use of such types; it is implementation defined whether operators
that are predefined for ``any real type'' are defined for a particular
nonstandard real type. In any case, such types are not permitted as
explicit_generic_actual_parameters for formal scalar types -- see
12.5.2.
NOTES
9. (32) As stated, real literals are of the anonymous predefined real type
universal_real. Other real types have no literals. However, the overload
resolution rules, see 8.6, allow expressions of the type universal_real
whenever a real type is expected.
ΓòÉΓòÉΓòÉ 6.5.7. Floating Point Types ΓòÉΓòÉΓòÉ
1. For floating point types, the error bound is specified as a relative
precision by giving the required minimum number of significant decimal
digits.
Syntax
2.
floating_point_definition ::=
digits static_expression [real_range_specification]
3.
real_range_specification ::=
range static_simple_expression ┬╖┬╖ static_simple_expression
Name Resolution Rules
4. The requested decimal precision, which is the minimum number of
significant decimal digits required for the floating point type, is
specified by the value of the expression given after the reserved word
digits. This expression is expected to be of any integer type.
5. Each simple_expression of a real_range_specification is expected to be of
any real type; the types need not be the same.
Legality Rules
6. The requested decimal precision shall be specified by a static expression
whose value is positive and no greater than System.Max_Base_Digits. Each
simple_expression of a real_range_specification shall also be static. If
the real_range_specification is omitted, the requested decimal precision
shall be no greater than System.Max_Digits.
7. A floating_point_definition is illegal if the implementation does not
support a floating point type that satisfies the requested decimal
precision and range.
Static Semantics
8. The set of values for a floating point type is the (infinite) set of
rational numbers. The machine numbers of a floating point type are the
values of the type that can be represented exactly in every unconstrained
variable of the type. The base range, see 3.5, of a floating point type
is symmetric around zero, except that it can include some extra negative
values in some implementations.
9. The base decimal precision of a floating point type is the number of
decimal digits of precision representable in objects of the type. The
safe range of a floating point type is that part of its base range for
which the accuracy corresponding to the base decimal precision is
preserved by all predefined operations.
10. A floating_point_definition defines a floating point type whose base
decimal precision is no less than the requested decimal precision. If a
real_range_specification is given, the safe range of the floating point
type (and hence, also its base range) includes at least the values of the
simple expressions given in the real_range_specification. If a
real_range_specification is not given, the safe (and base) range of the
type includes at least the values of the range -10.0**(4*D) ┬╖┬╖
+10.0**(4*D) where D is the requested decimal precision. The safe range
might include other values as well. The attributes Safe_First and
Safe_Last give the actual bounds of the safe range.
11. A floating_point_definition also defines a first subtype of the type. If
a real_range_specification is given, then the subtype is constrained to a
range whose bounds are given by a conversion of the values of the
simple_expressions of the real_range_specification to the type being
defined. Otherwise, the subtype is unconstrained.
12. There is a predefined, unconstrained, floating point subtype named Float,
declared in the visible part of package Standard.
Dynamic Semantics
13. The elaboration of a floating_point_definition creates the floating point
type and its first subtype.
Implementation Requirements
14. In an implementation that supports floating point types with 6 or more
digits of precision, the requested decimal precision for Float shall be
at least 6.
15. If Long_Float is predefined for an implementation, then its requested
decimal precision shall be at least 11.
Implementation Permissions
16. An implementation is allowed to provide additional predefined floating
point types, declared in the visible part of Standard, whose
(unconstrained) first subtypes have names of the form Short_Float,
Long_Float, Short_Short_Float, Long_Long_Float, etc. Different predefined
floating point types are allowed to have the same base decimal precision.
However, the precision of Float should be no greater than that of
Long_Float. Similarly, the precision of Short_Float (if provided) should
be no greater than Float. Corresponding recommendations apply to any
other predefined floating point types. There need not be a named floating
point type corresponding to each distinct base decimal precision
supported by an implementation.
Implementation Advice
17. An implementation should support Long_Float in addition to Float if the
target machine supports 11 or more digits of precision. No other named
floating point subtypes are recommended for package Standard. Instead,
appropriate named floating point subtypes should be provided in the
library package Interfaces, see B.2.
NOTES
18. (33) If a floating point subtype is unconstrained, then assignments to
variables of the subtype involve only Overflow_Checks, never
Range_Checks.
Examples
19. Examples of floating point types and subtypes:
20.
type Coefficient is digits 10 range -1.0 ┬╖┬╖ 1.0;
21.
type Real is digits 8;
type Mass is digits 7 range 0.0 ┬╖┬╖ 1.0E35;
22.
subtype Probability is Real range 0.0 ┬╖┬╖ 1.0;
-- a subtype with a smaller range
ΓòÉΓòÉΓòÉ 6.5.8. Operations of Floating Point Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The following attribute is defined for every floating point subtype S:
2. S'Digits
S'Digits denotes the requested decimal precision for the
subtype S. The value of this attribute is of the type
universal_integer. The requested decimal precision of the
base subtype of a floating point type T is defined to be the
largest value of d for which ceiling(d * log(10) /
log(T'Machine_Radix)) + 1 <= T'Model_Mantissa.
NOTES
3. (34) The predefined operations of a floating point type include the
assignment operation, qualification, the membership tests, and explicit
conversion to and from other numeric types. They also include the
relational operators and the following predefined arithmetic operators:
the binary and unary adding operators - and +, certain multiplying
operators, the unary operator abs, and the exponentiation operator.
4. (35) As for all types, objects of a floating point type have Size and
Address attributes, see 13.3. Other attributes of floating point types
are defined in A.5.3.
ΓòÉΓòÉΓòÉ 6.5.9. Fixed Point Types ΓòÉΓòÉΓòÉ
1. A fixed point type is either an ordinary fixed point type, or a decimal
fixed point type. The error bound of a fixed point type is specified as
an absolute value, called the delta of the fixed point type.
Syntax
2.
fixed_point_definition ::=
ordinary_fixed_point_definition | decimal_fixed_point_definition
3.
ordinary_fixed_point_definition ::=
delta static_expression real_range_specification
4.
decimal_fixed_point_definition ::=
delta static_expression digits static_expression
[real_range_specification]
5.
digits_constraint ::=
digits static_expression [range_constraint]
Name Resolution Rules
6. For a type defined by a fixed_point_definition, the delta of the type is
specified by the value of the expression given after the reserved word
delta; this expression is expected to be of any real type. For a type
defined by a decimal_fixed_point_definition (a decimal fixed point type),
the number of significant decimal digits for its first subtype (the
digits of the first subtype) is specified by the expression given after
the reserved word digits; this expression is expected to be of any
integer type.
Legality Rules
7. In a fixed_point_definition or digits_constraint, the expressions given
after the reserved words delta and digits shall be static; their values
shall be positive.
8. The set of values of a fixed point type comprise the integral multiples
of a number called the small of the type. For a type defined by an
ordinary_fixed_point_definition (an ordinary fixed point type), the small
may be specified by an attribute_definition_clause, see 13.3, if so
specified, it shall be no greater than the delta of the type. If not
specified, the small of an ordinary fixed point type is an
implementation-defined power of two less than or equal to the delta.
9. For a decimal fixed point type, the small equals the delta; the delta
shall be a power of 10. If a real_range_specification is given, both
bounds of the range shall be in the range -(10**digits-1)*delta ┬╖┬╖
+(10**digits-1)*delta.
10. A fixed_point_definition is illegal if the implementation does not
support a fixed point type with the given small and specified range or
digits.
11. For a subtype_indication with a digits_constraint, the subtype_mark shall
denote a decimal fixed point subtype.
Static Semantics
12. The base range, see 3.5 of a fixed point type is symmetric around zero,
except possibly for an extra negative value in some implementations.
13. An ordinary_fixed_point_definition defines an ordinary fixed point type
whose base range includes at least all multiples of small that are
between the bounds specified in the real_range_specification. The base
range of the type does not necessarily include the specified bounds
themselves. An ordinary_fixed_point_definition also defines a constrained
first subtype of the type, with each bound of its range given by the
closer to zero of:
a. the value of the conversion to the fixed point type of the
corresponding expression of the real_range_specification;
b. the corresponding bound of the base range.
1. A decimal_fixed_point_definition defines a decimal fixed point type whose
base range includes at least the range -(10**digits-1)*delta ┬╖┬╖
+(10**digits-1)*delta. A decimal_fixed_point_definition also defines a
constrained first subtype of the type. If a real_range_specification is
given, the bounds of the first subtype are given by a conversion of the
values of the expressions of the real_range_specification. Otherwise, the
range of the first subtype is -(10**digits-1)*delta ┬╖┬╖
+(10**digits-1)*delta.
Dynamic Semantics
2. The elaboration of a fixed_point_definition creates the fixed point type
and its first subtype.
3. For a digits_constraint on a decimal fixed point subtype with a given
delta, if it does not have a range_constraint, then it specifies an
implicit range -(10**D-1)*delta ┬╖┬╖ +(10**D-1)*delta, where D is the value
of the expression. A digits_constraint is compatible with a decimal fixed
point subtype if the value of the expression is no greater than the
digits of the subtype, and if it specifies (explicitly or implicitly) a
range that is compatible with the subtype.
4. The elaboration of a digits_constraint consists of the elaboration of the
range_constraint, if any. If a range_constraint is given, a check is made
that the bounds of the range are both in the range -(10**D-1)*delta ┬╖┬╖
+(10**D-1)*delta, where D is the value of the (static) expression given
after the reserved word digits. If this check fails, Constraint_Error is
raised.
Implementation Requirements
5. The implementation shall support at least 24 bits of precision (including
the sign bit) for fixed point types.
Implementation Permissions
6. Implementations are permitted to support only smalls that are a power of
two. In particular, all decimal fixed point type declarations can be
disallowed. Note however that conformance with the Information Systems
Annex requires support for decimal smalls, and decimal fixed point type
declarations with digits up to at least 18.
NOTES
7. (36) The base range of an ordinary fixed point type need not include the
specified bounds themselves so that the range specification can be given
in a natural way, such as:
8.
type Fraction is delta 2.0**(-15) range -1.0 ┬╖┬╖ 1.0;
9. With 2's complement hardware, such a type could have a signed 16-bit
representation, using 1 bit for the sign and 15 bits for fraction,
resulting in a base range of -1.0 ┬╖┬╖ 1.0-2.0**(-15).
Examples
10. Examples of fixed point types and subtypes:
11.
type Volt is delta 0.125 range 0.0 ┬╖┬╖ 255.0;
12.
-- A pure fraction which requires all the available
-- space in a word can be declared as the type Fraction:
type Fraction is delta System.Fine_Delta range -1.0 ┬╖┬╖ 1.0;
-- Fraction'Last = 1.0 - System.Fine_Delta
13.
type Money is delta 0.01 digits 15; -- decimal fixed point
subtype Salary is Money digits 10;
-- Money'Last = 10.0**13 - 0.01, Salary'Last = 10.0**8 - 0.01
ΓòÉΓòÉΓòÉ 6.5.10. Operations of Fixed Point Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The following attributes are defined for every fixed point subtype S:
2. S'Small
S'Small denotes the small of the type of S. The value of
this attribute is of the type universal_real. Small may
be specified for nonderived fixed point types via an
attribute_definition_clause, see 13.3; the expression
of such a clause shall be static.
3. S'Delta
S'Delta denotes the delta of the fixed point subtype S. The
value of this attribute is of the type universal_real.
4. S'Fore
S'Fore yields the minimum number of characters needed
before the decimal point for the decimal representation
of any value of the subtype S, assuming that the
representation does not include an exponent, but
includes a one-character prefix that is either a minus
sign or a space. (This minimum number does not include
superfluous zeros or underlines, and is at least 2.) The
value of this attribute is of the type
universal_integer.
5. S'Aft
S'Aft yields the number of decimal digits needed after the
decimal point to accommodate the delta of the subtype S,
unless the delta of the subtype S is greater than 0.1, in
which case the attribute yields the value one. (S'Aft is the
smallest positive integer N for which (10**N)*S'Delta is
greater than or equal to one.) The value of this attribute
is of the type universal_integer.
6. The following additional attributes are defined for every decimal fixed
point subtype S:
7. S'Digits
S'Digits denotes the digits of the decimal fixed point
subtype S, which corresponds to the number of decimal digits
that are representable in objects of the subtype. The value
of this attribute is of the type universal_integer. Its
value is determined as follows:
a. For a first subtype or a subtype defined by a subtype_indication
with a digits_constraint, the digits is the value of the expression
given after the reserved word digits;
b. For a subtype defined by a subtype_indication without a
digits_constraint, the digits of the subtype is the same as that of
the subtype denoted by the subtype_mark in the subtype_indication.
c. The digits of a base subtype is the largest integer D such that the
range -(10**D-1)*delta ┬╖┬╖ +(10**D-1)*delta is included in the base
range of the type.
1. S'Scale
S'Scale denotes the scale of the subtype S, defined as the
value N such that S'Delta = 10.0**(-N). The scale indicates
the position of the point relative to the rightmost
significant digits of values of subtype S. The value of this
attribute is of the type universal_integer.
2. S'Round S'Round denotes a function with the following specification:
a.
function S'Round(X : universal_real)
return S'Base
b. The function returns the value obtained by rounding X (away from 0,
if X is midway between two values of the type of S).
NOTES
1. (37) All subtypes of a fixed point type will have the same value for the
Delta attribute, in the absence of delta_constraints, see J.3.
2. (38) S'Scale is not always the same as S'Aft for a decimal subtype; for
example, if S'Delta = 1.0 then S'Aft is 1 while S'Scale is 0.
3. (39) The predefined operations of a fixed point type include the
assignment operation, qualification, the membership tests, and explicit
conversion to and from other numeric types. They also include the
relational operators and the following predefined arithmetic operators:
the binary and unary adding operators - and +, multiplying operators, and
the unary operator abs.
4. (40) As for all types, objects of a fixed point type have Size and
Address attributes, see 13.3. Other attributes of fixed point types are
defined in A.5.4.
ΓòÉΓòÉΓòÉ 6.6. Array Types ΓòÉΓòÉΓòÉ
1. An array object is a composite object consisting of components which all
have the same subtype. The name for a component of an array uses one or
more index values belonging to specified discrete types. The value of an
array object is a composite value consisting of the values of the
components.
Syntax
2.
array_type_definition ::=
unconstrained_array_definition | constrained_array_definition
3.
unconstrained_array_definition ::=
array(index_subtype_definition {, index_subtype_definition})
of component_definition
4.
index_subtype_definition ::= subtype_mark range <>
5.
constrained_array_definition ::=
array (discrete_subtype_definition
{, discrete_subtype_definition}) of component_definition
6.
discrete_subtype_definition ::= discrete_subtype_indication | range
7.
component_definition ::= [aliased] subtype_indication
Name Resolution Rules
8. For a discrete_subtype_definition that is a range, the range shall
resolve to be of some specific discrete type; which discrete type shall
be determined without using any context other than the bounds of the
range itself (plus the preference for root_integer -- see 8.6.).
Legality Rules
9. Each index_subtype_definition or discrete_subtype_definition in an
array_type_definition defines an index subtype; its type (the index type)
shall be discrete.
10. The subtype defined by the subtype_indication of a component_definition
(the component subtype) shall be a definite subtype.
11. Within the definition of a nonlimited composite type (or a limited
composite type that later in its immediate scope becomes nonlimited --
7.3.1, and 7.5.), if a component_definition contains the reserved word
aliased and the type of the component is discriminated, then the nominal
subtype of the component shall be constrained.
Static Semantics
12. An array is characterized by the number of indices (the dimensionality of
the array), the type and position of each index, the lower and upper
bounds for each index, and the subtype of the components. The order of
the indices is significant.
13. A one-dimensional array has a distinct component for each possible index
value. A multidimensional array has a distinct component for each
possible sequence of index values that can be formed by selecting one
value for each index position (in the given order). The possible values
for a given index are all the values between the lower and upper bounds,
inclusive; this range of values is called the index range. The bounds of
an array are the bounds of its index ranges. The length of a dimension of
an array is the number of values of the index range of the dimension
(zero for a null range). The length of a one-dimensional array is the
length of its only dimension.
14. An array_type_definition defines an array type and its first subtype. For
each object of this array type, the number of indices, the type and
position of each index, and the subtype of the components are as in the
type definition; the values of the lower and upper bounds for each index
belong to the corresponding index subtype of its type, except for null
arrays, see 3.6.1.
15. An unconstrained_array_definition defines an array type with an
unconstrained first subtype. Each index_subtype_definition defines the
corresponding index subtype to be the subtype denoted by the
subtype_mark. The compound delimiter <> (called a box) of an
index_subtype_definition stands for an undefined range (different objects
of the type need not have the same bounds).
16. A constrained_array_definition defines an array type with a constrained
first subtype. Each discrete_subtype_definition defines the corresponding
index subtype, as well as the corresponding index range for the
constrained first subtype. The constraint of the first subtype consists
of the bounds of the index ranges.
17. The discrete subtype defined by a discrete_subtype_definition is either
that defined by the subtype_indication, or a subtype determined by the
range as follows:
a. If the type of the range resolves to root_integer, then the
discrete_subtype_definition defines a subtype of the predefined type
Integer with bounds given by a conversion to Integer of the bounds
of the range;
b. Otherwise, the discrete_subtype_definition defines a subtype of the
type of the range, with the bounds given by the range.
1. The component_definition of an array_type_definition defines the nominal
subtype of the components. If the reserved word aliased appears in the
component_definition, then each component of the array is aliased, see
3.10.
Dynamic Semantics
2. The elaboration of an array_type_definition creates the array type and
its first subtype, and consists of the elaboration of any
discrete_subtype_definitions and the component_definition.
3. The elaboration of a discrete_subtype_definition creates the discrete
subtype, and consists of the elaboration of the subtype_indication or the
evaluation of the range. The elaboration of a component_definition in an
array_type_definition consists of the elaboration of the
subtype_indication. The elaboration of any discrete_subtype_definitions
and the elaboration of the component_definition are performed in an
arbitrary order.
NOTES
4. (41) All components of an array have the same subtype. In particular, for
an array of components that are one-dimensional arrays, this means that
all components have the same bounds and hence the same length.
5. (42) Each elaboration of an array_type_definition creates a distinct
array type. A consequence of this is that each object whose
object_declaration contains an array_type_definition is of its own unique
type.
Examples
6. Examples of type declarations with unconstrained array definitions:
7.
type Vector is array(Integer range <>) of Real;
type Matrix is array(Integer range <>, Integer range <>)
of Real;
type Bit_Vector is array(Integer range <>) of Boolean;
type Roman is array(Positive range <>) of
Roman_Digit; -- see 3.5.2
8. Examples of type declarations with constrained array definitions:
9.
type Table is array(1 ┬╖┬╖ 10) of Integer;
type Schedule is array(Day) of Boolean;
type Line is array(1 ┬╖┬╖ Max_Line_Size) of Character;
10. Examples of object declarations with array type definitions:
11.
Grid : array(1 ┬╖┬╖ 80, 1 ┬╖┬╖ 100) of Boolean;
Mix : array(Color range Red ┬╖┬╖ Green) of Boolean;
Page : array(Positive range <>) of Line := -- an array of arrays
(1 | 50 => Line'(1 | Line'Last => '+', others => '-'),
-- see 4.3.3
2 ┬╖┬╖ 49 => Line'(1 | Line'Last => '|', others => ' '));
-- Page is constrained by its initial value to (1┬╖┬╖50)
3.6.1 Index Constraints and Discrete Ranges
3.6.2 Operations of Array Types
3.6.3 String Types
ΓòÉΓòÉΓòÉ 6.6.1. Index Constraints and Discrete Ranges ΓòÉΓòÉΓòÉ
1. An index_constraint determines the range of possible values for every
index of an array subtype, and thereby the corresponding array bounds.
Syntax
2.
index_constraint ::= (discrete_range {, discrete_range})
3.
discrete_range ::= discrete_subtype_indication | range
Name Resolution Rules
4. The type of a discrete_range is the type of the subtype defined by the
subtype_indication, or the type of the range. For an index_constraint,
each discrete_range shall resolve to be of the type of the corresponding
index.
Legality Rules
5. An index_constraint shall appear only in a subtype_indication whose
subtype_mark denotes either an unconstrained array subtype, or an
unconstrained access subtype whose designated subtype is an unconstrained
array subtype; in either case, the index_constraint shall provide a
discrete_range for each index of the array type.
Static Semantics
6. A discrete_range defines a range whose bounds are given by the range, or
by the range of the subtype defined by the subtype_indication.
Dynamic Semantics
7. An index_constraint is compatible with an unconstrained array subtype if
and only if the index range defined by each discrete_range is compatible,
see 3.5, with the corresponding index subtype. If any of the
discrete_ranges defines a null range, any array thus constrained is a
null array, having no components. An array value satisfies an
index_constraint if at each index position the array value and the
index_constraint have the same index bounds.
8. The elaboration of an index_constraint consists of the evaluation of the
discrete_range(s), in an arbitrary order. The evaluation of a
discrete_range consists of the elaboration of the subtype_indication or
the evaluation of the range.
NOTES
9. (43) The elaboration of a subtype_indication consisting of a subtype_mark
followed by an index_constraint checks the compatibility of the
index_constraint with the subtype_mark, see 3.2.2.
10. (44) Even if an array value does not satisfy the index constraint of an
array subtype, Constraint_Error is not raised on conversion to the array
subtype, so long as the length of each dimension of the array value and
the array subtype match (see 4.6).
Examples
11. Examples of array declarations including an index constraint:
12.
Board : Matrix(1 ┬╖┬╖ 8, 1 ┬╖┬╖ 8); -- see 3.6
Rectangle : Matrix(1 ┬╖┬╖ 20, 1 ┬╖┬╖ 30);
Inverse : Matrix(1 ┬╖┬╖ N, 1 ┬╖┬╖ N); -- N need not be static
13.
Filter : Bit_Vector(0 ┬╖┬╖ 31);
14. Example of array declaration with a constrained array subtype:
15.
My_Schedule : Schedule;
-- all arrays of type Schedule have the same bounds
16. Example of record type with a component that is an array:
17.
type Var_Line(Length : Natural) is
record
Image : String(1 ┬╖┬╖ Length);
end record;
18.
Null_Line : Var_Line(0); -- Null_Line.Image is a null array
ΓòÉΓòÉΓòÉ 6.6.2. Operations of Array Types ΓòÉΓòÉΓòÉ
Legality Rules
1. The argument N used in the attribute_designators for the N-th dimension
of an array shall be a static expression of some integer type. The value
of N shall be positive (nonzero) and no greater than the dimensionality
of the array.
Static Semantics
2. The following attributes are defined for a prefix A that is of an array
type (after any implicit dereference), or denotes a constrained array
subtype:
3. A'First
A'First denotes the lower bound of the first index range; its
type is the corresponding index type.
4. A'First(N)
A'First(N) denotes the lower bound of the N-th index range;
its type is the corresponding index type.
5. A'Last
A'Last denotes the upper bound of the first index range; its
type is the corresponding index type.
6. A'Last(N)
A'Last(N) denotes the upper bound of the N-th index range;
its type is the corresponding index type.
7. A'Range
A'Range is equivalent to the range A'First ┬╖┬╖ A'Last, except
that the prefix A is only evaluated once.
8. A'Range(N)
A'Range(N) is equivalent to the range A'First(N) ┬╖┬╖
A'Last(N), except that the prefix A is only evaluated once.
9. A'Length
A'Length denotes the number of values of the first index
range (zero for a null range); its type is universal_integer.
10. A'Length(N)
A'Length(N) denotes the number of values of the N-th index
range (zero for a null range); its type is universal_integer.
Implementation Advice
11. An implementation should normally represent multidimensional arrays in
row-major order, consistent with the notation used for multidimensional
array aggregates, see 4.3.3. However, if a pragma Convention(Fortran,
┬╖┬╖┬╖) applies to a multidimensional array type, then column-major order
should be used instead, see B.5: ``Interfacing with Fortran''.
NOTES
12. (45) The attribute_references A'First and A'First(1) denote the same
value. A similar relation exists for the attribute_references A'Last,
A'Range, and A'Length. The following relation is satisfied (except for a
null array) by the above attributes if the index type is an integer type:
13.
A'Length(N) = A'Last(N) - A'First(N) + 1
14. (46) An array type is limited if its component type is limited, see 7.5.
15. (47) The predefined operations of an array type include the membership
tests, qualification, and explicit conversion. If the array type is not
limited, they also include assignment and the predefined equality
operators. For a one-dimensional array type, they include the predefined
concatenation operators (if nonlimited) and, if the component type is
discrete, the predefined relational operators; if the component type is
boolean, the predefined logical operators are also included.
16. (48) A component of an array can be named with an indexed_component. A
value of an array type can be specified with an array_aggregate, unless
the array type is limited. For a one-dimensional array type, a slice of
the array can be named; also, string literals are defined if the
component type is a character type.
Examples
17. Examples (using arrays declared in the examples of subclause 3.6.1):
18.
-- Filter'First = 0
-- Filter'Last = 31
-- Filter'Length = 32
-- Rectangle'Last(1) = 20
-- Rectangle'Last(2) = 30
ΓòÉΓòÉΓòÉ 6.6.3. String Types ΓòÉΓòÉΓòÉ
Static Semantics
1. A one-dimensional array type whose component type is a character type is
called a string type.
2. There are two predefined string types, String and Wide_String, each
indexed by values of the predefined subtype Positive; these are declared
in the visible part of package Standard:
3.
subtype Positive is Integer range 1 ┬╖┬╖ Integer'Last;
4.
type String is array(Positive range <>) of Character;
type Wide_String is array(Positive range <>) of Wide_Character;
NOTES
5. (49) String literals, see 2.6, and 4.2, are defined for all string types.
The concatenation operator & is predefined for string types, as for all
nonlimited one-dimensional array types. The ordering operators <, <=, >,
and >= are predefined for string types, as for all one-dimensional
discrete array types; these ordering operators correspond to
lexicographic order, see 4.5.2.
Examples
6. Examples of string objects:
7.
Stars : String(1 ┬╖┬╖ 120) := (1 ┬╖┬╖ 120 => '*' );
Question : constant String := "How many characters?";
-- Question'First = 1, Question'Last = 20
-- Question'Length = 20 (the number of characters)
8.
Ask_Twice : String := Question & Question;
-- constrained to (1┬╖┬╖40)
Ninety_Six : constant Roman := "XCVI";
-- see 3.5.2, and 3.6
ΓòÉΓòÉΓòÉ 6.7. Discriminants ΓòÉΓòÉΓòÉ
1. A composite type (other than an array type) can have discriminants, which
parameterize the type. A known_discriminant_part specifies the
discriminants of a composite type. A discriminant of an object is a
component of the object, and is either of a discrete type or an access
type. An unknown_discriminant_part in the declaration of a partial view
of a type specifies that the discriminants of the type are unknown for
the given view; all subtypes of such a partial view are indefinite
subtypes.
Syntax
2.
discriminant_part ::=
unknown_discriminant_part | known_discriminant_part
3.
unknown_discriminant_part ::= (<>)
4.
known_discriminant_part ::=
(discriminant_specification {; discriminant_specification})
5.
discriminant_specification ::=
defining_identifier_list : subtype_mark
[:= default_expression]
| defining_identifier_list : access_definition
[:= default_expression]
6.
default_expression ::= expression
Name Resolution Rules
7. The expected type for the default_expression of a
discriminant_specification is that of the corresponding discriminant.
Legality Rules
8. A known_discriminant_part is only permitted in a declaration for a
composite type that is not an array type (this includes generic formal
types); a type declared with a known_discriminant_part is called a
discriminated type, as is a type that inherits (known) discriminants.
9. The subtype of a discriminant may be defined by a subtype_mark, in which
case the subtype_mark shall denote a discrete or access subtype, or it
may be defined by an access_definition (in which case the subtype_mark of
the access_definition may denote any kind of subtype). A discriminant
that is defined by an access_definition is called an access discriminant
and is of an anonymous general access-to-variable type whose designated
subtype is denoted by the subtype_mark of the access_definition.
10. A discriminant_specification for an access discriminant shall appear only
in the declaration for a task or protected type, or for a type with the
reserved word limited in its (full) definition or in that of one of its
ancestors. In addition to the places where Legality Rules normally apply,
see 12.3, this rule applies also in the private part of an instance of a
generic unit.
11. Default_expressions shall be provided either for all or for none of the
discriminants of a known_discriminant_part. No default_expressions are
permitted in a known_discriminant_part in a declaration of a tagged type
or a generic formal type.
12. For a type defined by a derived_type_definition, if a
known_discriminant_part is provided in its declaration, then:
a. The parent subtype shall be constrained;
b. If the parent type is not a tagged type, then each discriminant of
the derived type shall be used in the constraint defining the parent
subtype;
c. If a discriminant is used in the constraint defining the parent
subtype, the subtype of the discriminant shall be statically
compatible (see 4.9.1) with the subtype of the corresponding parent
discriminant.
1. The type of the default_expression, if any, for an access discriminant
shall be convertible to the anonymous access type of the discriminant
(see 4.6).
Static Semantics
2. A discriminant_specification declares a discriminant; the subtype_mark
denotes its subtype unless it is an access discriminant, in which case
the discriminant's subtype is the anonymous access-to-variable subtype
defined by the access_definition.
3. For a type defined by a derived_type_definition, each discriminant of the
parent type is either inherited, constrained to equal some new
discriminant of the derived type, or constrained to the value of an
expression. When inherited or constrained to equal some new discriminant,
the parent discriminant and the discriminant of the derived type are said
to correspond. Two discriminants also correspond if there is some common
discriminant to which they both correspond. A discriminant corresponds to
itself as well. If a discriminant of a parent type is constrained to a
specific value by a derived_type_definition, then that discriminant is
said to be specified by that derived_type_definition.
4. A constraint that appears within the definition of a discriminated type
depends on a discriminant of the type if it names the discriminant as a
bound or discriminant value. A component_definition depends on a
discriminant if its constraint depends on the discriminant, or on a
discriminant that corresponds to it.
5. A component depends on a discriminant if:
a. Its component_definition depends on the discriminant; or
b. It is declared in a variant_part that is governed by the
discriminant; or
c. It is a component inherited as part of a derived_type_definition,
and the constraint of the parent_subtype_indication depends on the
discriminant; or
d. It is a subcomponent of a component that depends on the
discriminant.
1. Each value of a discriminated type includes a value for each component of
the type that does not depend on a discriminant; this includes the
discriminants themselves. The values of discriminants determine which
other component values are present in the value of the discriminated
type.
2. A type declared with a known_discriminant_part is said to have known
discriminants; its first subtype is unconstrained. A type declared with
an unknown_discriminant_part is said to have unknown discriminants. A
type declared without a discriminant_part has no discriminants, unless it
is a derived type; if derived, such a type has the same sort of
discriminants (known, unknown, or none) as its parent (or ancestor) type.
A tagged class-wide type also has unknown discriminants. Any subtype of a
type with unknown discriminants is an unconstrained and indefinite
subtype, see 3.2, and 3.3.
Dynamic Semantics
3. An access_definition is elaborated when the value of a corresponding
access discriminant is defined, either by evaluation of its
default_expression or by elaboration of a discriminant_constraint. The
elaboration of an access_definition creates the anonymous access type.
When the expression defining the access discriminant is evaluated, it is
converted to this anonymous access type, see 4.6.
NOTES
4. (50) If a discriminated type has default_expressions for its
discriminants, then unconstrained variables of the type are permitted,
and the values of the discriminants can be changed by an assignment to
such a variable. If defaults are not provided for the discriminants, then
all variables of the type are constrained, either by explicit constraint
or by their initial value; the values of the discriminants of such a
variable cannot be changed after initialization.
5. (51) The default_expression for a discriminant of a type is evaluated
when an object of an unconstrained subtype of the type is created.
6. (52) Assignment to a discriminant of an object (after its initialization)
is not allowed, since the name of a discriminant is a constant; neither
assignment_statements nor assignments inherent in passing as an in out or
out parameter are allowed. Note however that the value of a discriminant
can be changed by assigning to the enclosing object, presuming it is an
unconstrained variable.
7. (53) A discriminant that is of a named access type is not called an
access discriminant; that term is used only for discriminants defined by
an access_definition.
Examples
8. Examples of discriminated types:
9.
type Buffer(Size : Buffer_Size := 100) is -- see 3.5.4
record
Pos : Buffer_Size := 0;
Value : String(1 ┬╖┬╖ Size);
end record;
10.
type Matrix_Rec(Rows, Columns : Integer) is
record
Mat : Matrix(1 ┬╖┬╖ Rows, 1 ┬╖┬╖ Columns); -- see 3.6
end record;
11.
type Square(Side : Integer) is new
Matrix_Rec(Rows => Side, Columns => Side);
12.
type Double_Square(Number : Integer) is
record
Left : Square(Number);
Right : Square(Number);
end record;
type Item(Number : Positive) is
record
Content : Integer;
-- no component depends on the discriminant
end record;
3.7.1 Discriminant Constraints
3.7.2 Operations of Discriminated Types
ΓòÉΓòÉΓòÉ 6.7.1. Discriminant Constraints ΓòÉΓòÉΓòÉ
1. A discriminant_constraint specifies the values of the discriminants for a
given discriminated type.
Syntax
2.
discriminant_constraint ::=
(discriminant_association {, discriminant_association})
3.
discriminant_association ::=
[discriminant_selector_name
{| discriminant_selector_name} =>] expression
a. A discriminant_association is said to be named if it has one or more
discriminant_selector_names; it is otherwise said to be positional.
In a discriminant_constraint, any positional associations shall
precede any named associations.
Name Resolution Rules
1. Each selector_name of a named discriminant_association shall resolve to
denote a discriminant of the subtype being constrained; the discriminants
so named are the associated discriminants of the named association. For a
positional association, the associated discriminant is the one whose
discriminant_specification occurred in the corresponding position in the
known_discriminant_part that defined the discriminants of the subtype
being constrained.
2. The expected type for the expression in a discriminant_association is
that of the associated discriminant(s).
Legality Rules
3. A discriminant_constraint is only allowed in a subtype_indication whose
subtype_mark denotes either an unconstrained discriminated subtype, or an
unconstrained access subtype whose designated subtype is an unconstrained
discriminated subtype.
4. A named discriminant_association with more than one selector_name is
allowed only if the named discriminants are all of the same type. A
discriminant_constraint shall provide exactly one value for each
discriminant of the subtype being constrained.
5. The expression associated with an access discriminant shall be of a type
convertible to the anonymous access type.
Dynamic Semantics
6. A discriminant_constraint is compatible with an unconstrained
discriminated subtype if each discriminant value belongs to the subtype
of the corresponding discriminant.
7. A composite value satisfies a discriminant constraint if and only if each
discriminant of the composite value has the value imposed by the
discriminant constraint.
8. For the elaboration of a discriminant_constraint, the expressions in the
discriminant_associations are evaluated in an arbitrary order and
converted to the type of the associated discriminant (which might raise
Constraint_Error -- see 4.6.); the expression of a named association is
evaluated (and converted) once for each associated discriminant. The
result of each evaluation and conversion is the value imposed by the
constraint for the associated discriminant.
NOTES
9. (54) The rules of the language ensure that a discriminant of an object
always has a value, either from explicit or implicit initialization.
Examples
10. Examples (using types declared above in clause 3.7):
11.
Large : Buffer(200); -- constrained, always 200 characters
-- (explicit discriminant value)
Message : Buffer; -- unconstrained, initially 100 characters
-- (default discriminant value)
Basis : Square(5); -- constrained, always 5 by 5
Illegal : Square; -- illegal, a Square has to be constrained
ΓòÉΓòÉΓòÉ 6.7.2. Operations of Discriminated Types ΓòÉΓòÉΓòÉ
1. If a discriminated type has default_expressions for its discriminants,
then unconstrained variables of the type are permitted, and the
discriminants of such a variable can be changed by assignment to the
variable. For a formal parameter of such a type, an attribute is provided
to determine whether the corresponding actual parameter is constrained or
unconstrained.
Static Semantics
2. For a prefix A that is of a discriminated type (after any implicit
dereference), the following attribute is defined:
3. A'Constrained
Yields the value True if A denotes a constant, a value, or a
constrained variable, and False otherwise.
Erroneous Execution
4. The execution of a construct is erroneous if the construct has a
constituent that is a name denoting a subcomponent that depends on
discriminants, and the value of any of these discriminants is changed by
this execution between evaluating the name and the last use (within this
execution) of the subcomponent denoted by the name.
ΓòÉΓòÉΓòÉ 6.8. Record Types ΓòÉΓòÉΓòÉ
1. A record object is a composite object consisting of named components. The
value of a record object is a composite value consisting of the values of
the components.
Syntax
2.
record_type_definition ::=
[[abstract] tagged] [limited] record_definition
3.
record_definition ::=
record
component_list
end record
| null record
4.
component_list ::=
component_item {component_item}
| {component_item} variant_part
| null;
5.
component_item ::= component_declaration | representation_clause
6.
component_declaration ::=
defining_identifier_list : component_definition
[:= default_expression];
Name Resolution Rules
7. The expected type for the default_expression, if any, in a
component_declaration is the type of the component.
Legality Rules
8. A default_expression is not permitted if the component is of a limited
type.
9. Each component_declaration declares a component of the record type.
Besides components declared by component_declarations, the components of
a record type include any components declared by
discriminant_specifications of the record type declaration. The
identifiers of all components of a record type shall be distinct.
10. Within a type_declaration, a name that denotes a component, protected
subprogram, or entry of the type is allowed only in the following cases:
a. A name that denotes any component, protected subprogram, or entry is
allowed within a representation item that occurs within the
declaration of the composite type.
b. A name that denotes a noninherited discriminant is allowed within
the declaration of the type, but not within the discriminant_part.
If the discriminant is used to define the constraint of a component,
the bounds of an entry family, or the constraint of the parent
subtype in a derived_type_definition then its name shall appear
alone as a direct_name (not as part of a larger expression or
expanded name). A discriminant shall not be used to define the
constraint of a scalar component.
1. If the name of the current instance of a type, see 8.6, is used to define
the constraint of a component, then it shall appear as a direct_name that
is the prefix of an attribute_reference whose result is of an access
type, and the attribute_reference shall appear alone.
Static Semantics
2. The component_definition of a component_declaration defines the (nominal)
subtype of the component. If the reserved word aliased appears in the
component_definition, then the component is aliased, see 3.10.
3. If the component_list of a record type is defined by the reserved word
null and there are no discriminants, then the record type has no
components and all records of the type are null records. A
record_definition of null record is equivalent to record null; end
record.
Dynamic Semantics
4. The elaboration of a record_type_definition creates the record type and
its first subtype, and consists of the elaboration of the
record_definition. The elaboration of a record_definition consists of the
elaboration of its component_list, if any.
5. The elaboration of a component_list consists of the elaboration of the
component_items and variant_part, if any, in the order in which they
appear. The elaboration of a component_declaration consists of the
elaboration of the component_definition.
6. Within the definition of a composite type, if a component_definition or
discrete_subtype_definition, see 9.5.2, includes a name that denotes a
discriminant of the type, or that is an attribute_reference whose prefix
denotes the current instance of the type, the expression containing the
name is called a per-object expression, and the constraint being defined
is called a per-object constraint. For the elaboration of a
component_definition of a component_declaration, if the constraint of the
subtype_indication is not a per-object constraint, then the
subtype_indication is elaborated. On the other hand, if the constraint is
a per-object constraint, then the elaboration consists of the evaluation
of any included expression that is not part of a per-object expression.
NOTES
7. (55) A component_declaration with several identifiers is equivalent to a
sequence of single component_declarations, as explained in 3.3.1.
8. (56) The default_expression of a record component is only evaluated upon
the creation of a default-initialized object of the record type
(presuming the object has the component, if it is in a variant_part --
see 3.3.1).
9. (57) The subtype defined by a component_definition, see 3.6, has to be a
definite subtype.
10. (58) If a record type does not have a variant_part, then the same
components are present in all values of the type.
11. (59) A record type is limited if it has the reserved word limited in its
definition, or if any of its components are limited, see 7.5.
12. (60) The predefined operations of a record type include membership tests,
qualification, and explicit conversion. If the record type is nonlimited,
they also include assignment and the predefined equality operators.
13. (61) A component of a record can be named with a selected_component. A
value of a record can be specified with a record_aggregate, unless the
record type is limited.
Examples
14. Examples of record type declarations:
15.
type Date is
record
Day : Integer range 1 ┬╖┬╖ 31;
Month : Month_Name;
Year : Integer range 0 ┬╖┬╖ 4000;
end record;
16.
type Complex is
record
Re : Real := 0.0;
Im : Real := 0.0;
end record;
17. Examples of record variables:
18.
Tomorrow, Yesterday : Date;
A, B, C : Complex;
19.
-- both components of A, B, and C are implicitly initialized to zero
3.8.1 Variant Parts and Discrete Choices
ΓòÉΓòÉΓòÉ 6.8.1. Variant Parts and Discrete Choices ΓòÉΓòÉΓòÉ
1. A record type with a variant_part specifies alternative lists of
components. Each variant defines the components for the value or values
of the discriminant covered by its discrete_choice_list.
Syntax
2.
variant_part ::=
case discriminant_direct_name is
variant
{variant}
end case;
3.
variant ::=
when discrete_choice_list =>
component_list
4.
discrete_choice_list ::= discrete_choice {| discrete_choice}
5.
discrete_choice ::= expression | discrete_range | others
Name Resolution Rules
6. The discriminant_direct_name shall resolve to denote a discriminant
(called the discriminant of the variant_part) specified in the
known_discriminant_part of the full_type_declaration that contains the
variant_part. The expected type for each discrete_choice in a variant is
the type of the discriminant of the variant_part.
Legality Rules
7. The discriminant of the variant_part shall be of a discrete type.
8. The expressions and discrete_ranges given as discrete_choices in a
variant_part shall be static. The discrete_choice others shall appear
alone in a discrete_choice_list, and such a discrete_choice_list, if it
appears, shall be the last one in the enclosing construct.
9. A discrete_choice is defined to cover a value in the following cases:
a. A discrete_choice that is an expression covers a value if the value
equals the value of the expression converted to the expected type.
b. A discrete_choice that is a discrete_range covers all values
(possibly none) that belong to the range.
c. The discrete_choice others covers all values of its expected type
that are not covered by previous discrete_choice_lists of the same
construct.
1. A discrete_choice_list covers a value if one of its discrete_choices
covers the value.
2. The possible values of the discriminant of a variant_part shall be
covered as follows:
a. If the discriminant is of a static constrained scalar subtype, then
each non-others discrete_choice shall cover only values in that
subtype, and each value of that subtype shall be covered by some
discrete_choice (either explicitly or by others);
b. If the type of the discriminant is a descendant of a generic formal
scalar type then the variant_part shall have an others
discrete_choice;
c. Otherwise, each value of the base range of the type of the
discriminant shall be covered (either explicitly or by others).
1. Two distinct discrete_choices of a variant_part shall not cover the same
value.
Static Semantics
2. If the component_list of a variant is specified by null, the variant has
no components.
3. The discriminant of a variant_part is said to govern the variant_part and
its variants. In addition, the discriminant of a derived type governs a
variant_part and its variants if it corresponds, see 3.7, to the
discriminant of the variant_part.
Dynamic Semantics
4. A record value contains the values of the components of a particular
variant only if the value of the discriminant governing the variant is
covered by the discrete_choice_list of the variant. This rule applies in
turn to any further variant that is, itself, included in the
component_list of the given variant.
5. The elaboration of a variant_part consists of the elaboration of the
component_list of each variant in the order in which they appear.
Examples
6. Example of record type with a variant part:
7.
type Device is (Printer, Disk, Drum);
type State is (Open, Closed);
8.
type Peripheral(Unit : Device := Disk) is
record
Status : State;
case Unit is
when Printer =>
Line_Count : Integer range 1 ┬╖┬╖ Page_Size;
when others =>
Cylinder : Cylinder_Index;
Track : Track_Number;
end case;
end record;
9. Examples of record subtypes:
10.
subtype Drum_Unit is Peripheral(Drum);
subtype Disk_Unit is Peripheral(Disk);
11. Examples of constrained record variables:
12.
Writer : Peripheral(Unit => Printer);
Archive : Disk_Unit;
ΓòÉΓòÉΓòÉ 6.9. Tagged Types and Type Extensions ΓòÉΓòÉΓòÉ
1. Tagged types and type extensions support object-oriented programming,
based on inheritance with extension and run-time polymorphism via
dispatching operations.
Static Semantics
2. A record type or private type that has the reserved word tagged in its
declaration is called a tagged type. When deriving from a tagged type,
additional components may be defined. As for any derived type, additional
primitive subprograms may be defined, and inherited primitive subprograms
may be overridden. The derived type is called an extension of the
ancestor type, or simply a type extension. Every type extension is also a
tagged type, and is either a record extension or a private extension of
some other tagged type. A record extension is defined by a
derived_type_definition with a record_extension_part. A private
extension, which is a partial view of a record extension, can be declared
in the visible part of a package, see 7.3, or in a generic formal part,
see 12.5.1.
3. An object of a tagged type has an associated (run-time) tag that
identifies the specific tagged type used to create the object originally.
The tag of an operand of a class-wide tagged type T'Class controls which
subprogram body is to be executed when a primitive subprogram of type T
is applied to the operand, see 3.9.2, using a tag to control which body
to execute is called dispatching.
4. The tag of a specific tagged type identifies the full_type_declaration of
the type. If a declaration for a tagged type occurs within a
generic_package_declaration, then the corresponding type declarations in
distinct instances of the generic package are associated with distinct
tags. For a tagged type that is local to a generic package body, the
language does not specify whether repeated instantiations of the generic
body result in distinct tags.
5. The following language-defined library package exists:
6.
package Ada.Tags is
type Tag is private;
7.
function Expanded_Name(T : Tag) return String;
function External_Tag(T : Tag) return String;
function Internal_Tag(External : String) return Tag;
8.
Tag_Error : exception;
9.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Tags;
10. The function Expanded_Name returns the full expanded name of the first
subtype of the specific type identified by the tag, in upper case,
starting with a root library unit. The result is implementation defined
if the type is declared within an unnamed block_statement.
11. The function External_Tag returns a string to be used in an external
representation for the given tag. The call External_Tag(S'Tag) is
equivalent to the attribute_reference S'External_Tag, see 13.3.
12. The function Internal_Tag returns the tag that corresponds to the given
external tag, or raises Tag_Error if the given string is not the external
tag for any specific type of the partition.
13. For every subtype S of a tagged type T (specific or class-wide), the
following attributes are defined:
14. S'Class
S'Class denotes a subtype of the class-wide type (called
T'Class in this International Standard) for the class rooted
at T (or if S already denotes a class-wide subtype, then
S'Class is the same as S).
a. S'Class is unconstrained. However, if S is constrained, then the
values of S'Class are only those that when converted to the type T
belong to S.
1. S'Tag
S'Tag denotes the tag of the type T (or if T is class-wide,
the tag of the root type of the corresponding class). The
value of this attribute is of type Tag.
2. Given a prefix X that is of a class-wide tagged type (after any implicit
dereference), the following attribute is defined:
3. X'Tag
X'Tag denotes the tag of X. The value of this attribute is of
type Tag.
Dynamic Semantics
4. The tag associated with an object of a tagged type is determined as
follows:
a. The tag of a stand-alone object, a component, or an aggregate of a
specific tagged type T identifies T.
b. The tag of an object created by an allocator for an access type with
a specific designated tagged type T, identifies T.
c. The tag of an object of a class-wide tagged type is that of its
initialization expression.
d. The tag of the result returned by a function whose result type is a
specific tagged type T identifies T.
e. The tag of the result returned by a function with a class-wide
result type is that of the return expression.
1. The tag is preserved by type conversion and by parameter passing. The tag
of a value is the tag of the associated object, see 6.2.
Implementation Permissions
2. The implementation of the functions in Ada.Tags may raise Tag_Error if no
specific type corresponding to the tag passed as a parameter exists in
the partition at the time the function is called.
NOTES
3. (62) A type declared with the reserved word tagged should normally be
declared in a package_specification, so that new primitive subprograms
can be declared for it.
4. (63) Once an object has been created, its tag never changes.
5. (64) Class-wide types are defined to have unknown discriminants (see
3.7). This means that objects of a class-wide type have to be explicitly
initialized (whether created by an object_declaration or an allocator),
and that aggregates have to be explicitly qualified with a specific type
when their expected type is class-wide.
6. (65) If S denotes an untagged private type whose full type is tagged,
then S'Class is also allowed before the full type definition, but only in
the private part of the package in which the type is declared (see
7.3.1). Similarly, the Class attribute is defined for incomplete types
whose full type is tagged, but only within the library unit in which the
incomplete type is declared, see 3.10.1.
Examples
7. Examples of tagged record types:
8.
type Point is tagged
record
X, Y : Real := 0.0;
end record;
9.
type Expression is tagged null record;
-- Components will be added by each extension
3.9.1 Type Extensions
3.9.2 Dispatching Operations of Tagged Types
3.9.3 Abstract Types and Subprograms
ΓòÉΓòÉΓòÉ 6.9.1. Type Extensions ΓòÉΓòÉΓòÉ
1. Every type extension is a tagged type, and is either a record extension
or a private extension of some other tagged type.
Syntax
2.
record_extension_part ::= with record_definition
Legality Rules
3. The parent type of a record extension shall not be a class-wide type. If
the parent type is nonlimited, then each of the components of the
record_extension_part shall be nonlimited. The accessibility level (see
3.10.2) of a record extension shall not be statically deeper than that of
its parent type. In addition to the places where Legality Rules normally
apply, see 12.3, these rules apply also in the private part of an
instance of a generic unit.
4. A type extension shall not be declared in a generic body if the parent
type is declared outside that body.
Dynamic Semantics
5. The elaboration of a record_extension_part consists of the elaboration of
the record_definition.
NOTES
6. (66) The term ``type extension'' refers to a type as a whole. The term
``extension part'' refers to the piece of text that defines the
additional components (if any) the type extension has relative to its
specified ancestor type.
7. (67) The accessibility rules imply that a tagged type declared in a
library package_specification can be extended only at library level or as
a generic formal. When the extension is declared immediately within a
package_body, primitive subprograms are inherited and are overridable,
but new primitive subprograms cannot be added.
8. (68) A name that denotes a component (including a discriminant) of the
parent type is not allowed within the record_extension_part. Similarly, a
name that denotes a component defined within the record_extension_part is
not allowed within the record_extension_part. It is permissible to use a
name that denotes a discriminant of the record extension, providing there
is a new known_discriminant_part in the enclosing type declaration. (The
full rule is given in 3.8.)
9. (69) Each visible component of a record extension has to have a unique
name, whether the component is (visibly) inherited from the parent type
or declared in the record_extension_part, see 8.3.
Examples
10. Examples of record extensions (of types defined above in 3.9.):
11.
type Painted_Point is new Point with
record
Paint : Color := White;
end record;
-- Components X and Y are inherited
12.
Origin : constant Painted_Point := (X | Y => 0.0, Paint => Black);
13.
type Literal is new Expression with
record -- a leaf in an Expression tree
Value : Real;
end record;
14.
type Expr_Ptr is access all Expression'Class;
-- see 3.10
15.
type Binary_Operation is new Expression with
record -- an internal node in an Expression tree
Left, Right : Expr_Ptr;
end record;
16.
type Addition is new Binary_Operation with null record;
type Subtraction is new Binary_Operation with null record;
-- No additional components needed for these extensions
17.
Tree : Expr_Ptr := -- A tree representation of ``5.0 + (13.0-7.0)''
new Addition'(
Left => new Literal'(Value => 5.0),
Right => new Subtraction'(
Left => new Literal'(Value => 13.0),
Right => new Literal'(Value => 7.0)));
ΓòÉΓòÉΓòÉ 6.9.2. Dispatching Operations of Tagged Types ΓòÉΓòÉΓòÉ
1. The primitive subprograms of a tagged type are called dispatching
operations. A dispatching operation can be called using a statically
determined controlling tag, in which case the body to be executed is
determined at compile time. Alternatively, the controlling tag can be
dynamically determined, in which case the call dispatches to a body that
is determined at run time; such a call is termed a dispatching call. As
explained below, the properties of the operands and the context of a
particular call on a dispatching operation determine how the controlling
tag is determined, and hence whether or not the call is a dispatching
call. Run-time polymorphism is achieved when a dispatching operation is
called by a dispatching call.
Static Semantics
2. A call on a dispatching operation is a call whose name or prefix denotes
the declaration of a primitive subprogram of a tagged type, that is, a
dispatching operation. A controlling operand in a call on a dispatching
operation of a tagged type T is one whose corresponding formal parameter
is of type T or is of an anonymous access type with designated type T;
the corresponding formal parameter is called a controlling formal
parameter. If the controlling formal parameter is an access parameter,
the controlling operand is the object designated by the actual parameter,
rather than the actual parameter itself. If the call is to a (primitive)
function with result type T, then the call has a controlling result --
the context of the call can control the dispatching.
3. A name or expression of a tagged type is either statically tagged,
dynamically tagged, or tag indeterminate, according to whether, when used
as a controlling operand, the tag that controls dispatching is determined
statically by the operand's (specific) type, dynamically by its tag at
run time, or from context. A qualified_expression or parenthesized
expression is statically, dynamically, or indeterminately tagged
according to its operand. For other kinds of names and expressions, this
is determined as follows:
a. The name or expression is statically tagged if it is of a specific
tagged type and, if it is a call with a controlling result, it has
at least one statically tagged controlling operand;
b. The name or expression is dynamically tagged if it is of a
class-wide type, or it is a call with a controlling result and at
least one dynamically tagged controlling operand;
c. The name or expression is tag indeterminate if it is a call with a
controlling result, all of whose controlling operands (if any) are
tag indeterminate.
1. A type_conversion is statically or dynamically tagged according to
whether the type determined by the subtype_mark is specific or
class-wide, respectively. For a controlling operand that is designated by
an actual parameter, the controlling operand is statically or dynamically
tagged according to whether the designated type of the actual parameter
is specific or class-wide, respectively.
Legality Rules
2. A call on a dispatching operation shall not have both dynamically tagged
and statically tagged controlling operands.
3. If the expected type for an expression or name is some specific tagged
type, then the expression or name shall not be dynamically tagged unless
it is a controlling operand in a call on a dispatching operation.
Similarly, if the expected type for an expression is an anonymous
access-to-specific tagged type, then the expression shall not be of an
access-to-class-wide type unless it designates a controlling operand in a
call on a dispatching operation.
4. In the declaration of a dispatching operation of a tagged type,
everywhere a subtype of the tagged type appears as a subtype of the
profile, see 6.1, it shall statically match the first subtype of the
tagged type. If the dispatching operation overrides an inherited
subprogram, it shall be subtype conformant with the inherited subprogram.
A dispatching operation shall not be of convention Intrinsic. If a
dispatching operation overrides the predefined equals operator, then it
shall be of convention Ada (either explicitly or by default -- see
6.3.1.).
5. The default_expression for a controlling formal parameter of a
dispatching operation shall be tag indeterminate. A controlling formal
parameter that is an access parameter shall not have a
default_expression.
6. A given subprogram shall not be a dispatching operation of two or more
distinct tagged types.
7. The explicit declaration of a primitive subprogram of a tagged type shall
occur before the type is frozen, see 13.14. For example, new dispatching
operations cannot be added after objects or values of the type exist, nor
after deriving a record extension from it, nor after a body.
Dynamic Semantics
8. For the execution of a call on a dispatching operation of a type T, the
controlling tag value determines which subprogram body is executed. The
controlling tag value is defined as follows:
a. If one or more controlling operands are statically tagged, then the
controlling tag value is statically determined to be the tag of T.
b. If one or more controlling operands are dynamically tagged, then the
controlling tag value is not statically determined, but is rather
determined by the tags of the controlling operands. If there is more
than one dynamically tagged controlling operand, a check is made
that they all have the same tag. If this check fails,
Constraint_Error is raised unless the call is a function_call whose
name denotes the declaration of an equality operator (predefined or
user defined) that returns Boolean, in which case the result of the
call is defined to indicate inequality, and no subprogram_body is
executed. This check is performed prior to evaluating any
tag-indeterminate controlling operands.
c. If all of the controlling operands are tag-indeterminate, then:
1. If the call has a controlling result and is itself a (possibly
parenthesized or qualified) controlling operand of an enclosing
call on a dispatching operation of type T, then its controlling
tag value is determined by the controlling tag value of this
enclosing call;
2. Otherwise, the controlling tag value is statically determined
to be the tag of type T.
1. For the execution of a call on a dispatching operation, the body executed
is the one for the corresponding primitive subprogram of the specific
type identified by the controlling tag value. The body for an explicitly
declared dispatching operation is the corresponding explicit body for the
subprogram. The body for an implicitly declared dispatching operation
that is overridden is the body for the overriding subprogram, even if the
overriding occurs in a private part. The body for an inherited
dispatching operation that is not overridden is the body of the
corresponding subprogram of the parent or ancestor type.
NOTES
2. (70) The body to be executed for a call on a dispatching operation is
determined by the tag; it does not matter whether that tag is determined
statically or dynamically, and it does not matter whether the
subprogram's declaration is visible at the place of the call.
3. (71) This subclause covers calls on primitive subprograms of a tagged
type. Rules for tagged type membership tests are described in 4.5.2.
Controlling tag determination for an assignment_statement is described in
5.2.
4. (72) A dispatching call can dispatch to a body whose declaration is not
visible at the place of the call.
5. (73) A call through an access-to-subprogram value is never a dispatching
call, even if the access value designates a dispatching operation.
Similarly a call whose prefix denotes a subprogram_renaming_declaration
cannot be a dispatching call unless the renaming itself is the
declaration of a primitive subprogram.
ΓòÉΓòÉΓòÉ 6.9.3. Abstract Types and Subprograms ΓòÉΓòÉΓòÉ
1. An abstract type is a tagged type intended for use as a parent type for
type extensions, but which is not allowed to have objects of its own. An
abstract subprogram is a subprogram that has no body, but is intended to
be overridden at some point when inherited. Because objects of an
abstract type cannot be created, a dispatching call to an abstract
subprogram always dispatches to some overriding body.
Legality Rules
2. An abstract type is a specific type that has the reserved word abstract
in its declaration. Only a tagged type is allowed to be declared
abstract.
3. A subprogram declared by an abstract_subprogram_declaration, see 6.1, is
an abstract subprogram. If it is a primitive subprogram of a tagged type,
then the tagged type shall be abstract.
4. For a derived type, if the parent or ancestor type has an abstract
primitive subprogram, or a primitive function with a controlling result,
then:
a. If the derived type is abstract or untagged, the inherited
subprogram is abstract.
b. Otherwise, the subprogram shall be overridden with a nonabstract
subprogram; for a type declared in the visible part of a package,
the overriding may be either in the visible or the private part.
However, if the type is a generic formal type, the subprogram need
not be overridden for the formal type itself; a nonabstract version
will necessarily be provided by the actual type.
1. A call on an abstract subprogram shall be a dispatching call;
nondispatching calls to an abstract subprogram are not allowed.
2. The type of an aggregate, or of an object created by an
object_declaration or an allocator, or a generic formal object of mode
in, shall not be abstract. The type of the target of an assignment
operation, see 5.2, shall not be abstract. The type of a component shall
not be abstract. If the result type of a function is abstract, then the
function shall be abstract.
3. If a partial view is not abstract, the corresponding full view shall not
be abstract. If a generic formal type is abstract, then for each
primitive subprogram of the formal that is not abstract, the
corresponding primitive subprogram of the actual shall not be abstract.
4. For an abstract type declared in a visible part, an abstract primitive
subprogram shall not be declared in the private part, unless it is
overriding an abstract subprogram implicitly declared in the visible
part. For a tagged type declared in a visible part, a primitive function
with a controlling result shall not be declared in the private part,
unless it is overriding a function implicitly declared in the visible
part.
5. A generic actual subprogram shall not be an abstract subprogram. The
prefix of an attribute_reference for the Access, Unchecked_Access, or
Address attributes shall not denote an abstract subprogram.
NOTES
6. (74) Abstractness is not inherited; to declare an abstract type, the
reserved word abstract has to be used in the declaration of the type
extension.
7. (75) A class-wide type is never abstract. Even if a class is rooted at an
abstract type, the class-wide type for the class is not abstract, and an
object of the class-wide type can be created; the tag of such an object
will identify some nonabstract type in the class.
Examples
8. Example of an abstract type representing a set of natural numbers:
9.
package Sets is
subtype Element_Type is Natural;
type Set is abstract tagged null record;
function Empty return Set is abstract;
function Union(Left, Right : Set) return Set is abstract;
function Intersection(Left, Right : Set) return Set is abstract;
function Unit_Set(Element : Element_Type) return Set is abstract;
procedure Take
(Element : out Element_Type;
From : in out Set) is abstract;
end Sets;
NOTES
10. (76) Notes on the example: Given the above abstract type, one could then
derive various (nonabstract) extensions of the type, representing
alternative implementations of a set. One might use a bit vector, but
impose an upper bound on the largest element representable, while another
might use a hash table, trading off space for flexibility.
ΓòÉΓòÉΓòÉ 6.10. Access Types ΓòÉΓòÉΓòÉ
1. A value of an access type (an access value) provides indirect access to
the object or subprogram it designates. Depending on its type, an access
value can designate either subprograms, objects created by allocators
(see 4.8) or more generally aliased objects of an appropriate type.
Syntax
2.
access_type_definition ::=
access_to_object_definition
| access_to_subprogram_definition
3.
access_to_object_definition ::=
access [general_access_modifier] subtype_indication
4.
general_access_modifier ::= all | constant
5.
access_to_subprogram_definition ::=
access [protected] procedure parameter_profile
| access [protected] function parameter_and_result_profile
6.
access_definition ::= access subtype_mark
Static Semantics
7. There are two kinds of access types, access-to-object types, whose values
designate objects, and access-to-subprogram types, whose values designate
subprograms. Associated with an access-to-object type is a storage pool;
several access types may share the same storage pool. A storage pool is
an area of storage used to hold dynamically allocated objects (called
pool elements) created by allocators; storage pools are described further
in 13.11: ``Storage Management''.
8. Access-to-object types are further subdivided into pool-specific access
types, whose values can designate only the elements of their associated
storage pool, and general access types, whose values can designate the
elements of any storage pool, as well as aliased objects created by
declarations rather than allocators, and aliased subcomponents of other
objects.
9. A view of an object is defined to be aliased if it is defined by an
object_declaration or component_definition with the reserved word
aliased, or by a renaming of an aliased view. In addition, the
dereference of an access-to-object value denotes an aliased view, as does
a view conversion, see 4.6 of an aliased view. Finally, the current
instance of a limited type, and a formal parameter or generic formal
object of a tagged type are defined to be aliased. Aliased views are the
ones that can be designated by an access value. If the view defined by an
object_declaration is aliased, and the type of the object has
discriminants, then the object is constrained; if its nominal subtype is
unconstrained, then the object is constrained by its initial value.
Similarly, if the object created by an allocator has discriminants, the
object is constrained, either by the designated subtype, or by its
initial value.
10. An access_to_object_definition defines an access-to-object type and its
first subtype; the subtype_indication defines the designated subtype of
the access type. If a general_access_modifier appears, then the access
type is a general access type. If the modifier is the reserved word
constant, then the type is an access-to-constant type; a designated
object cannot be updated through a value of such a type. If the modifier
is the reserved word all, then the type is an access-to-variable type; a
designated object can be both read and updated through a value of such a
type. If no general_access_modifier appears in the
access_to_object_definition, the access type is a pool-specific
access-to-variable type.
11. An access_to_subprogram_definition defines an access-to-subprogram type
and its first subtype; the parameter_profile or
parameter_and_result_profile defines the designated profile of the access
type. There is a calling convention associated with the designated
profile; only subprograms with this calling convention can be designated
by values of the access type. By default, the calling convention is
``protected'' if the reserved word protected appears, and ``Ada''
otherwise. See Annex B for how to override this default.
12. An access_definition defines an anonymous general access-to-variable
type; the subtype_mark denotes its designated subtype. An
access_definition is used in the specification of an access discriminant,
see 3.7, or an access parameter, see 6.1.
13. For each (named) access type, there is a literal null which has a null
access value designating no entity at all. The null value of a named
access type is the default initial value of the type. Other values of an
access type are obtained by evaluating an attribute_reference for the
Access or Unchecked_Access attribute of an aliased view of an object or
non-intrinsic subprogram, or, in the case of a named access-to-object
type, an allocator, which returns an access value designating a newly
created object, see 3.10.2.
14. All subtypes of an access-to-subprogram type are constrained. The first
subtype of a type defined by an access_type_definition or an
access_to_object_definition is unconstrained if the designated subtype is
an unconstrained array or discriminated type; otherwise it is
constrained.
Dynamic Semantics
15. A composite_constraint is compatible with an unconstrained access subtype
if it is compatible with the designated subtype. An access value
satisfies a composite_constraint of an access subtype if it equals the
null value of its type or if it designates an object whose value
satisfies the constraint.
16. The elaboration of an access_type_definition creates the access type and
its first subtype. For an access-to-object type, this elaboration
includes the elaboration of the subtype_indication, which creates the
designated subtype.
17. The elaboration of an access_definition creates an anonymous general
access-to-variable type (this happens as part of the initialization of an
access parameter or access discriminant).
NOTES
18. (77) Access values are called ``pointers'' or ``references'' in some
other languages.
19. (78) Each access-to-object type has an associated storage pool; several
access types can share the same pool. An object can be created in the
storage pool of an access type by an allocator, see 4.8, for the access
type. A storage pool (roughly) corresponds to what some other languages
call a ``heap.''. See 13.11, for a discussion of pools.
20. (79) Only index_constraints and discriminant_constraints can be applied
to access types, see 3.6.1, and 3.7.1.
Examples
21. Examples of access-to-object types:
22.
type Peripheral_Ref is access Peripheral; -- see 3.8.1
type Binop_Ptr is access all Binary_Operation'Class;
-- general access-to-class-wide, see 3.9.1
23. Example of an access subtype:
24.
subtype Drum_Ref is Peripheral_Ref(Drum); -- see 3.8.1
25. Example of an access-to-subprogram type:
26.
type Message_Procedure is access
procedure (M : in String := "Error!");
procedure Default_Message_Procedure(M : in String);
Give_Message : Message_Procedure := Default_Message_Procedure'Access;
┬╖┬╖┬╖
procedure Other_Procedure(M : in String);
┬╖┬╖┬╖
Give_Message := Other_Procedure'Access;
┬╖┬╖┬╖
Give_Message("File not found.");
-- call with parameter (.all is optional)
Give_Message.all;
-- call with no parameters
3.10.1 Incomplete Type Declarations
3.10.2 Operations of Access Types
ΓòÉΓòÉΓòÉ 6.10.1. Incomplete Type Declarations ΓòÉΓòÉΓòÉ
1. There are no particular limitations on the designated type of an access
type. In particular, the type of a component of the designated type can
be another access type, or even the same access type. This permits
mutually dependent and recursive access types. An
incomplete_type_declaration can be used to introduce a type to be used as
a designated type, while deferring its full definition to a subsequent
full_type_declaration.
Syntax
2.
incomplete_type_declaration ::=
type defining_identifier [discriminant_part];
Legality Rules
3. An incomplete_type_declaration requires a completion, which shall be a
full_type_declaration. If the incomplete_type_declaration occurs
immediately within either the visible part of a package_specification or
a declarative_part, then the full_type_declaration shall occur later and
immediately within this visible part or declarative_part. If the
incomplete_type_declaration occurs immediately within the private part of
a given package_specification, then the full_type_declaration shall occur
later and immediately within either the private part itself, or the
declarative_part of the corresponding package_body.
4. If an incomplete_type_declaration has a known_discriminant_part, then a
full_type_declaration that completes it shall have a fully conforming
(explicit) known_discriminant_part, see 6.3.1. If an
incomplete_type_declaration has no discriminant_part (or an
unknown_discriminant_part), then a corresponding full_type_declaration is
nevertheless allowed to have discriminants, either explicitly, or
inherited via derivation.
5. The only allowed uses of a name that denotes an
incomplete_type_declaration are as follows:
a. as the subtype_mark in the subtype_indication of an
access_to_object_definition; the only form of constraint allowed in
this subtype_indication is a discriminant_constraint;
b. as the subtype_mark defining the subtype of a parameter or result of
an access_to_subprogram_definition;
c. as the subtype_mark in an access_definition;
d. as the prefix of an attribute_reference whose attribute_designator
is Class; such an attribute_reference is similarly restricted to the
uses allowed here; when used in this way, the corresponding
full_type_declaration shall declare a tagged type, and the
attribute_reference shall occur in the same library unit as the
incomplete_type_declaration.
1. A dereference (whether implicit or explicit -- see 4.1.) shall not be of
an incomplete type.
Static Semantics
2. An incomplete_type_declaration declares an incomplete type and its first
subtype; the first subtype is unconstrained if a known_discriminant_part
appears.
Dynamic Semantics
3. The elaboration of an incomplete_type_declaration has no effect.
NOTES
4. (80) Within a declarative_part, an incomplete_type_declaration and a
corresponding full_type_declaration cannot be separated by an intervening
body. This is because a type has to be completely defined before it is
frozen, and a body freezes all types declared prior to it in the same
declarative_part, see 13.14.
Examples
5. Example of a recursive type:
6.
type Cell; -- incomplete type declaration
type Link is access Cell;
7.
type Cell is
record
Value : Integer;
Succ : Link;
Pred : Link;
end record;
8.
Head : Link := new Cell'(0, null, null);
Next : Link := Head.Succ;
9. Examples of mutually dependent access types:
10.
type Person(<>); -- incomplete type declaration
type Car; -- incomplete type declaration
11.
type Person_Name is access Person;
type Car_Name is access all Car;
12.
type Car is
record
Number : Integer;
Owner : Person_Name;
end record;
13.
type Person(Sex : Gender) is
record
Name : String(1 ┬╖┬╖ 20);
Birth : Date;
Age : Integer range 0 ┬╖┬╖ 130;
Vehicle : Car_Name;
case Sex is
when M => Wife : Person_Name(Sex => F);
when F => Husband : Person_Name(Sex => M);
end case;
end record;
14.
My_Car, Your_Car, Next_Car : Car_Name := new Car;
-- see 4.8
George : Person_Name := new Person(M);
┬╖┬╖┬╖
George.Vehicle := Your_Car;
ΓòÉΓòÉΓòÉ 6.10.2. Operations of Access Types ΓòÉΓòÉΓòÉ
1. The attribute Access is used to create access values designating aliased
objects and non-intrinsic subprograms. The ``accessibility'' rules
prevent dangling references (in the absence of uses of certain unchecked
features -- see 13.).
Name Resolution Rules
2. For an attribute_reference with attribute_designator Access (or
Unchecked_Access -- see 13.10.), the expected type shall be a single
access type; the prefix of such an attribute_reference is never
interpreted as an implicit_dereference. If the expected type is an
access-to-subprogram type, then the expected profile of the prefix is the
designated profile of the access type.
Static Semantics
3. The accessibility rules, which prevent dangling references, are written
in terms of accessibility levels, which reflect the run-time nesting of
masters. As explained in 7.6.1, a master is the execution of a task_body,
a block_statement, a subprogram_body, an entry_body, or an
accept_statement. An accessibility level is deeper than another if it is
more deeply nested at run time. For example, an object declared local to
a called subprogram has a deeper accessibility level than an object
declared local to the calling subprogram. The accessibility rules for
access types require that the accessibility level of an object designated
by an access value be no deeper than that of the access type. This
ensures that the object will live at least as long as the access type,
which in turn ensures that the access value cannot later designate an
object that no longer exists. The Unchecked_Access attribute may be used
to circumvent the accessibility rules.
4. A given accessibility level is said to be statically deeper than another
if the given level is known at compile time (as defined below) to be
deeper than the other for all possible executions. In most cases,
accessibility is enforced at compile time by Legality Rules. Run-time
accessibility checks are also used, since the Legality Rules do not cover
certain cases involving access parameters and generic packages.
5. Each master, and each entity and view created by it, has an accessibility
level:
a. The accessibility level of a given master is deeper than that of
each dynamically enclosing master, and deeper than that of each
master upon which the task executing the given master directly
depends, see 9.3.
b. An entity or view created by a declaration has the same
accessibility level as the innermost enclosing master, except in the
cases of renaming and derived access types described below. A
parameter of a master has the same accessibility level as the
master.
c. The accessibility level of a view of an object or subprogram defined
by a renaming_declaration is the same as that of the renamed view.
d. The accessibility level of a view conversion is the same as that of
the operand.
e. For a function whose result type is a return-by-reference type, the
accessibility level of the result object is the same as that of the
master that elaborated the function body. For any other function,
the accessibility level of the result object is that of the
execution of the called function.
f. The accessibility level of a derived access type is the same as that
of its ultimate ancestor.
g. The accessibility level of the anonymous access type of an access
discriminant is the same as that of the containing object or
associated constrained subtype.
h. The accessibility level of the anonymous access type of an access
parameter is the same as that of the view designated by the actual.
If the actual is an allocator, this is the accessibility level of
the execution of the called subprogram.
i. The accessibility level of an object created by an allocator is the
same as that of the access type.
j. The accessibility level of a view of an object or subprogram denoted
by a dereference of an access value is the same as that of the
access type.
k. The accessibility level of a component, protected subprogram, or
entry of (a view of) a composite object is the same as that of (the
view of) the composite object.
1. One accessibility level is defined to be statically deeper than another
in the following cases:
a. For a master that is statically nested within another master, the
accessibility level of the inner master is statically deeper than
that of the outer master.
b. The statically deeper relationship does not apply to the
accessibility level of the anonymous type of an access parameter;
that is, such an accessibility level is not considered to be
statically deeper, nor statically shallower, than any other.
c. For determining whether one level is statically deeper than another
when within a generic package body, the generic package is presumed
to be instantiated at the same level as where it was declared;
run-time checks are needed in the case of more deeply nested
instantiations.
d. For determining whether one level is statically deeper than another
when within the declarative region of a type_declaration, the
current instance of the type is presumed to be an object created at
a deeper level than that of the type.
1. The accessibility level of all library units is called the library level;
a library-level declaration or entity is one whose accessibility level is
the library level.
2. The following attribute is defined for a prefix X that denotes an aliased
view of an object:
3. X'Access
X'Access yields an access value that designates the object
denoted by X. The type of X'Access is an access-to-object
type, as determined by the expected type. The expected type
shall be a general access type. X shall denote an aliased
view of an object, including possibly the current instance
(see 8.6) of a limited type within its definition, or a
formal parameter or generic formal object of a tagged type.
The view denoted by the prefix X shall satisfy the following
additional requirements, presuming the expected type for
X'Access is the general access type A:
1. If A is an access-to-variable type, then the view shall be a
variable; on the other hand, if A is an access-to-constant
type, the view may be either a constant or a variable.
2. The view shall not be a subcomponent that depends on
discriminants of a variable whose nominal subtype is
unconstrained, unless this subtype is indefinite, or the
variable is aliased.
3. If the designated type of A is tagged, then the type of the
view shall be covered by the designated type; if A's designated
type is not tagged, then the type of the view shall be the
same, and either A's designated subtype shall statically match
the nominal subtype of the view, or the designated subtype
shall be discriminated and unconstrained;
4. The accessibility level of the view shall not be statically
deeper than that of the access type A. In addition to the
places where Legality Rules normally apply, see 12.3, this rule
applies also in the private part of an instance of a generic
unit.
a. A check is made that the accessibility level of X is not deeper than
that of the access type A. If this check fails, Program_Error is
raised.
b. If the nominal subtype of X does not statically match the designated
subtype of A, a view conversion of X to the designated subtype is
evaluated (which might raise Constraint_Error -- see 4.6.) and the
value of X'Access designates that view.
1. The following attribute is defined for a prefix P that denotes a
subprogram:
2. P'Access
P'Access yields an access value that designates the
subprogram denoted by P. The type of P'Access is an
access-to-subprogram type (S), as determined by the expected
type. The accessibility level of P shall not be statically
deeper than that of S. In addition to the places where
Legality Rules normally apply, see 12.3, this rule applies
also in the private part of an instance of a generic unit.
The profile of P shall be subtype-conformant with the
designated profile of S, and shall not be Intrinsic. If
the subprogram denoted by P is declared within a generic
body, S shall be declared within the generic body.
NOTES
3. (81) The Unchecked_Access attribute yields the same result as the Access
attribute for objects, but has fewer restrictions, see 13.10. There are
other predefined operations that yield access values: an allocator can be
used to create an object, and return an access value that designates it,
see 4.8, evaluating the literal null yields a null access value that
designates no entity at all, see 4.2.
4. (82) The predefined operations of an access type also include the
assignment operation, qualification, and membership tests. Explicit
conversion is allowed between general access types with matching
designated subtypes; explicit conversion is allowed between
access-to-subprogram types with subtype conformant profiles, see 4.6.
Named access types have predefined equality operators; anonymous access
types do not, see 4.5.2.
5. (83) The object or subprogram designated by an access value can be named
with a dereference, either an explicit_dereference or an
implicit_dereference (see 4.1).
6. (84) A call through the dereference of an access-to-subprogram value is
never a dispatching call.
7. (85) The accessibility rules imply that it is not possible to use the
Access attribute to implement ``downward closures'' -- that is, to pass a
more-nested subprogram as a parameter to a less-nested subprogram, as
might be desired for example for an iterator abstraction. Instead,
downward closures can be implemented using generic formal subprograms
(see 12.6). Note that Unchecked_Access is not allowed for subprograms.
8. (86) Note that using an access-to-class-wide tagged type with a
dispatching operation is a potentially more structured alternative to
using an access-to-subprogram type.
9. (87) An implementation may consider two access-to-subprogram values to be
unequal, even though they designate the same subprogram. This might be
because one points directly to the subprogram, while the other points to
a special prologue that performs an Elaboration_Check and then jumps to
the subprogram (see 4.5.2).
Examples
10. Example of use of the Access attribute:
11.
Martha : Person_Name := new Person(F); -- see 3.10.1
Cars : array (1┬╖┬╖2) of aliased Car;
┬╖┬╖┬╖
Martha.Vehicle := Cars(1)'Access;
George.Vehicle := Cars(2)'Access;
ΓòÉΓòÉΓòÉ 6.11. Declarative Parts ΓòÉΓòÉΓòÉ
1. A declarative_part contains declarative_items (possibly none).
Syntax
2.
declarative_part ::= {declarative_item}
3.
declarative_item ::= basic_declarative_item | body
4.
basic_declarative_item ::=
basic_declaration | representation_clause | use_clause
5.
body ::= proper_body | body_stub
6.
proper_body ::=
subprogram_body | package_body | task_body | protected_body
Dynamic Semantics
7. The elaboration of a declarative_part consists of the elaboration of the
declarative_items, if any, in the order in which they are given in the
declarative_part.
8. An elaborable construct is in the elaborated state after the normal
completion of its elaboration. Prior to that, it is not yet elaborated.
9. For a construct that attempts to use a body, a check (Elaboration_Check)
is performed, as follows:
a. For a call to a (non-protected) subprogram that has an explicit
body, a check is made that the subprogram_body is already
elaborated. This check and the evaluations of any actual parameters
of the call are done in an arbitrary order.
b. For a call to a protected operation of a protected type (that has a
body -- no check is performed if a pragma Import applies to the
protected type), a check is made that the protected_body is already
elaborated. This check and the evaluations of any actual parameters
of the call are done in an arbitrary order.
c. For the activation of a task, a check is made by the activator that
the task_body is already elaborated. If two or more tasks are being
activated together, see 9.2, as the result of the elaboration of a
declarative_part or the initialization for the object created by an
allocator, this check is done for all of them before activating any
of them.
d. For the instantiation of a generic unit that has a body, a check is
made that this body is already elaborated. This check and the
evaluation of any explicit_generic_actual_parameters of the
instantiation are done in an arbitrary order.
1. The exception Program_Error is raised if any of these checks fails.
3.11.1 Completions of Declarations
ΓòÉΓòÉΓòÉ 6.11.1. Completions of Declarations ΓòÉΓòÉΓòÉ
1. Declarations sometimes come in two parts. A declaration that requires a
second part is said to require completion. The second part is called the
completion of the declaration (and of the entity declared), and is either
another declaration, a body, or a pragma.
Name Resolution Rules
2. A construct that can be a completion is interpreted as the completion of
a prior declaration only if:
a. The declaration and the completion occur immediately within the same
declarative region;
b. The defining name or defining_program_unit_name in the completion is
the same as in the declaration, or in the case of a pragma, the
pragma applies to the declaration;
c. If the declaration is overloadable, then the completion either has a
type-conformant profile, or is a pragma.
Legality Rules
1. An implicit declaration shall not have a completion. For any explicit
declaration that is specified to require completion, there shall be a
corresponding explicit completion.
2. At most one completion is allowed for a given declaration. Additional
requirements on completions appear where each kind of completion is
defined.
3. A type is completely defined at a place that is after its full type
definition (if it has one) and after all of its subcomponent types are
completely defined. A type shall be completely defined before it is
frozen, see 13.14, and 7.3.
NOTES
4. (88) Completions are in principle allowed for any kind of explicit
declaration. However, for some kinds of declaration, the only allowed
completion is a pragma Import, and implementations are not required to
support pragma Import for every kind of entity.
5. (89) There are rules that prevent premature uses of declarations that
have a corresponding completion. The Elaboration_Checks (see 3.11)
prevent such uses at run time for subprograms, protected operations,
tasks, and generic units. The "Freezing Rules" (see 13.14) prevent, at
compile time, premature uses of other entities such as private types and
deferred constants.
ΓòÉΓòÉΓòÉ 7. Names and Expressions ΓòÉΓòÉΓòÉ
1. The rules applicable to the different forms of name and expression, and
to their evaluation, are given in this section.
4.1 Names
4.2 Literals
4.3 Aggregates
4.4 Expressions
4.5 Operators and Expression Evaluation
4.6 Type Conversions
4.7 Qualified Expressions
4.8 Allocators
4.9 Static Expressions and Static Subtypes --- The
Detailed Node Listing ---
4.1 Names
4.1.1 Indexed Components
4.1.2 Slices
4.1.3 Selected Components
4.1.4 Attributes
4.2 Literals
4.3 Aggregates
4.3.1 Record Aggregates
4.3.2 Extension Aggregates
4.3.3 Array Aggregates
4.4 Expressions
4.5 Operators and Expression Evaluation
4.5.1 Logical Operators and Short-circuit Control
Forms
4.5.2 Relational Operators and Membership Tests
4.5.3 Binary Adding Operators
4.5.4 Unary Adding Operators
4.5.5 Multiplying Operators
4.5.6 Highest Precedence Operators
4.6 Type Conversions
4.7 Qualified Expressions
4.8 Allocators
4.9 Static Expressions and Static Subtypes
4.9.1 Statically Matching Constraints and Subtypes
ΓòÉΓòÉΓòÉ 7.1. Names ΓòÉΓòÉΓòÉ
1. Names can denote declared entities, whether declared explicitly or
implicitly, see 3.1. Names can also denote objects or subprograms
designated by access values; the results of type_conversions or
function_calls; subcomponents and slices of objects and values; protected
subprograms, single entries, entry families, and entries in families of
entries. Finally, names can denote attributes of any of the foregoing.
Syntax
2.
name ::=
direct_name | explicit_dereference
| indexed_component | slice
| selected_component | attribute_reference
| type_conversion | function_call
| character_literal
3.
direct_name ::= identifier | operator_symbol
4.
prefix ::= name | implicit_dereference
5.
explicit_dereference ::= name.all
6.
implicit_dereference ::= name
7. Certain forms of name (indexed_components, selected_components, slices,
and attributes) include a prefix that is either itself a name that
denotes some related entity, or an implicit_dereference of an access
value that designates some related entity.
Name Resolution Rules
8. The name in a dereference (either an implicit_dereference or an
explicit_dereference) is expected to be of any access type.
Static Semantics
9. If the type of the name in a dereference is some access-to-object type T,
then the dereference denotes a view of an object, the nominal subtype of
the view being the designated subtype of T.
10. If the type of the name in a dereference is some access-to-subprogram
type S, then the dereference denotes a view of a subprogram, the profile
of the view being the designated profile of S.
Dynamic Semantics
11. The evaluation of a name determines the entity denoted by the name. This
evaluation has no other effect for a name that is a direct_name or a
character_literal.
12. The evaluation of a name that has a prefix includes the evaluation of the
prefix. The evaluation of a prefix consists of the evaluation of the name
or the implicit_dereference. The prefix denotes the entity denoted by the
name or the implicit_dereference.
13. The evaluation of a dereference consists of the evaluation of the name
and the determination of the object or subprogram that is designated by
the value of the name. A check is made that the value of the name is not
the null access value. Constraint_Error is raised if this check fails.
The dereference denotes the object or subprogram designated by the value
of the name.
Examples
14. Examples of direct names:
15.
Pi -- the direct name of a number (see 3.3.2)
Limit -- the direct name of a constant (see 3.3.1)
Count -- the direct name of a scalar variable (see 3.3.1)
Board -- the direct name of an array variable (see 3.6.1)
Matrix -- the direct name of a type (see 3.6)
Random -- the direct name of a function (see 6.1)
Error -- the direct name of an exception (see 11.1)
16. Examples of dereferences:
17.
Next_Car.all -- explicit dereference denoting the object
-- designated by the access variable Next_Car,
-- see 3.10.1
Next_Car.Owner -- selected component with implicit dereference;
-- same as Next_Car.all.Owner
4.1.1 Indexed Components
4.1.2 Slices
4.1.3 Selected Components
4.1.4 Attributes
ΓòÉΓòÉΓòÉ 7.1.1. Indexed Components ΓòÉΓòÉΓòÉ
1. An indexed_component denotes either a component of an array or an entry
in a family of entries.
Syntax
2.
indexed_component ::= prefix(expression {, expression})
Name Resolution Rules
3. The prefix of an indexed_component with a given number of expressions
shall resolve to denote an array (after any implicit dereference) with
the corresponding number of index positions, or shall resolve to denote
an entry family of a task or protected object (in which case there shall
be only one expression).
4. The expected type for each expression is the corresponding index type.
Static Semantics
5. When the prefix denotes an array, the indexed_component denotes the
component of the array with the specified index value(s). The nominal
subtype of the indexed_component is the component subtype of the array
type.
6. When the prefix denotes an entry family, the indexed_component denotes
the individual entry of the entry family with the specified index value.
Dynamic Semantics
7. For the evaluation of an indexed_component, the prefix and the
expressions are evaluated in an arbitrary order. The value of each
expression is converted to the corresponding index type. A check is made
that each index value belongs to the corresponding index range of the
array or entry family denoted by the prefix. Constraint_Error is raised
if this check fails.
Examples
8. Examples of indexed components:
9.
My_Schedule(Sat)
-- a component of a one-dimensional array (see see 3.6.1)
Page(10)
-- a component of a one-dimensional array (see see 3.6)
Board(M, J + 1)
-- a component of a two-dimensional array (see see 3.6.1)
Page(10)(20)
-- a component of a component (see see 3.6)
Request(Medium)
-- an entry in a family of entries (see see 9.1)
Next_Frame(L)(M, N)
-- a component of a function call (see see 6.1)
NOTES
10. (1) Notes on the examples: Distinct notations are used for components of
multidimensional arrays (such as Board) and arrays of arrays (such as
Page). The components of an array of arrays are arrays and can therefore
be indexed. Thus Page(10)(20) denotes the 20th component of Page(10). In
the last example Next_Frame(L) is a function call returning an access
value that designates a two-dimensional array.
ΓòÉΓòÉΓòÉ 7.1.2. Slices ΓòÉΓòÉΓòÉ
1. A slice denotes a one-dimensional array formed by a sequence of
consecutive components of a one-dimensional array. A slice of a variable
is a variable; a slice of a constant is a constant; a slice of a value is
a value.
Syntax
2.
slice ::= prefix(discrete_range)
Name Resolution Rules
3. The prefix of a slice shall resolve to denote a one-dimensional array
(after any implicit dereference).
4. The expected type for the discrete_range of a slice is the index type of
the array type.
Static Semantics
5. A slice denotes a one-dimensional array formed by the sequence of
consecutive components of the array denoted by the prefix, corresponding
to the range of values of the index given by the discrete_range.
6. The type of the slice is that of the prefix. Its bounds are those defined
by the discrete_range.
Dynamic Semantics
7. For the evaluation of a slice, the prefix and the discrete_range are
evaluated in an arbitrary order. If the slice is not a null slice (a
slice where the discrete_range is a null range), then a check is made
that the bounds of the discrete_range belong to the index range of the
array denoted by the prefix. Constraint_Error is raised if this check
fails.
NOTES
8. (2) A slice is not permitted as the prefix of an Access
attribute_reference, even if the components or the array as a whole are
aliased (see 3.10.2).
9. (3) For a one-dimensional array A, the slice A(N ┬╖┬╖ N) denotes an array
that has only one component; its type is the type of A. On the other
hand, A(N) denotes a component of the array A and has the corresponding
component type.
Examples
10. Examples of slices:
11.
Stars(1 ┬╖┬╖ 15)
-- a slice of 15 characters (see 3.6.3)
Page(10 ┬╖┬╖ 10 + Size)
-- a slice of 1 + Size components (see 3.6)
Page(L)(A ┬╖┬╖ B)
-- a slice of the array Page(L) (see 3.6)
Stars(1 ┬╖┬╖ 0)
-- a null slice (see 3.6.3)
My_Schedule(Weekday)
-- bounds given by subtype (see 3.6.1, and 3.5.1)
Stars(5 ┬╖┬╖ 15)(K)
-- same as Stars(K) (see 3.6.3)
-- provided that K is in 5 ┬╖┬╖ 15
ΓòÉΓòÉΓòÉ 7.1.3. Selected Components ΓòÉΓòÉΓòÉ
1. Selected_components are used to denote components (including
discriminants), entries, entry families, and protected subprograms; they
are also used as expanded names as described below.
Syntax
2.
selected_component ::= prefix . selector_name
3.
selector_name ::= identifier | character_literal | operator_symbol
Name Resolution Rules
4. A selected_component is called an expanded name if, according to the
visibility rules, at least one possible interpretation of its prefix
denotes a package or an enclosing named construct (directly, not through
a subprogram_renaming_declaration or generic_renaming_declaration).
5. A selected_component that is not an expanded name shall resolve to denote
one of the following:
a. A component (including a discriminant):
1. The prefix shall resolve to denote an object or value of some
non-array composite type (after any implicit dereference). The
selector_name shall resolve to denote a
discriminant_specification of the type, or, unless the type is
a protected type, a component_declaration of the type. The
selected_component denotes the corresponding component of the
object or value.
a. A single entry, an entry family, or a protected subprogram:
1. The prefix shall resolve to denote an object or value of some
task or protected type (after any implicit dereference). The
selector_name shall resolve to denote an entry_declaration or
subprogram_declaration occurring (implicitly or explicitly)
within the visible part of that type. The selected_component
denotes the corresponding entry, entry family, or protected
subprogram.
1. An expanded name shall resolve to denote a declaration that occurs
immediately within a named declarative region, as follows:
a. The prefix shall resolve to denote either a package (including the
current instance of a generic package, or a rename of a package), or
an enclosing named construct.
b. The selector_name shall resolve to denote a declaration that occurs
immediately within the declarative region of the package or
enclosing construct (the declaration shall be visible at the place
of the expanded name -- see 8.3.). The expanded name denotes that
declaration.
c. If the prefix does not denote a package, then it shall be a
direct_name or an expanded name, and it shall resolve to denote a
program unit (other than a package), the current instance of a type,
a block_statement, a loop_statement, or an accept_statement (in the
case of an accept_statement or entry_body, no family index is
allowed); the expanded name shall occur within the declarative
region of this construct. Further, if this construct is a callable
construct and the prefix denotes more than one such enclosing
callable construct, then the expanded name is ambiguous,
independently of the selector_name.
Dynamic Semantics
1. The evaluation of a selected_component includes the evaluation of the
prefix.
2. For a selected_component that denotes a component of a variant, a check
is made that the values of the discriminants are such that the value or
object denoted by the prefix has this component. The exception
Constraint_Error is raised if this check fails.
Examples
3. Examples of selected components:
4.
Tomorrow.Month
-- a record component (see 3.8)
Next_Car.Owner
-- a record component (see 3.10.1)
Next_Car.Owner.Age
-- a record component (see 3.10.1)
-- the previous two lines involve implicit dereferences
Writer.Unit
-- a record component (a discriminant) (see 3.8.1)
Min_Cell(H).Value
-- a record component of the result (see 6.1)
-- of the function call Min_Cell(H)
Control.Seize
-- an entry of a protected object (see 9.4)
Pool(K).Write
-- an entry of the task Pool(K) (see 9.4)
5. Examples of expanded names:
6.
Key_Manager."<"
-- an operator of the visible part of a package (see 7.3.1)
Dot_Product.Sum
-- a variable declared in a function body (see 6.1)
Buffer.Pool
-- a variable declared in a protected unit (see 9.11)
Buffer.Read
-- an entry of a protected unit (see 9.11)
Swap.Temp
-- a variable declared in a block statement (see 5.6)
Standard.Boolean
-- the name of a predefined type (see A.1)
ΓòÉΓòÉΓòÉ 7.1.4. Attributes ΓòÉΓòÉΓòÉ
1. An attribute is a characteristic of an entity that can be queried via an
attribute_reference or a range_attribute_reference.
Syntax
2.
attribute_reference ::= prefix'attribute_designator
3.
attribute_designator ::=
identifier[(static_expression)]
| Access | Delta | Digits
4.
range_attribute_reference ::= prefix'range_attribute_designator
5.
range_attribute_designator ::= Range[(static_expression)]
Name Resolution Rules
6. In an attribute_reference, if the attribute_designator is for an
attribute defined for (at least some) objects of an access type, then the
prefix is never interpreted as an implicit_dereference; otherwise (and
for all range_attribute_references), if the type of the name within the
prefix is of an access type, the prefix is interpreted as an
implicit_dereference. Similarly, if the attribute_designator is for an
attribute defined for (at least some) functions, then the prefix is never
interpreted as a parameterless function_call; otherwise (and for all
range_attribute_references), if the prefix consists of a name that
denotes a function, it is interpreted as a parameterless function_call.
7. The expression, if any, in an attribute_designator or
range_attribute_designator is expected to be of any integer type.
Legality Rules
8. The expression, if any, in an attribute_designator or
range_attribute_designator shall be static.
Static Semantics
9. An attribute_reference denotes a value, an object, a subprogram, or some
other kind of program entity.
10. A range_attribute_reference X'Range(N) is equivalent to the range
X'First(N) ┬╖┬╖ X'Last(N), except that the prefix is only evaluated once.
Similarly, X'Range is equivalent to X'First ┬╖┬╖ X'Last, except that the
prefix is only evaluated once.
Dynamic Semantics
11. The evaluation of an attribute_reference (or range_attribute_reference)
consists of the evaluation of the prefix.
Implementation Permissions
12. An implementation may provide implementation-defined attributes; the
identifier for an implementation-defined attribute shall differ from
those of the language-defined attributes.
NOTES
13. (4) Attributes are defined throughout this International Standard, and
are summarized in K: ``Annex K.''.
14. (5) In general, the name in a prefix of an attribute_reference (or a
range_attribute_reference) has to be resolved without using any context.
However, in the case of the Access attribute, the expected type for the
prefix has to be a single access type, and if it is an
access-to-subprogram type, see 3.10.2, then the resolution of the name
can use the fact that the profile of the callable entity denoted by the
prefix has to be type conformant with the designated profile of the
access type.
Examples
15. Examples of attributes:
16.
Color'First
-- minimum value of the enumeration type Color (see 3.5.1)
Rainbow'Base'First
-- same as Color'First (see 3.5.1)
Real'Digits
-- precision of the type Real (see 3.5.7)
Board'Last(2)
-- upper bound of the second dimension of Board (see 3.6.1)
Board'Range(1)
-- index range of the first dimension of Board (see 3.6.1)
Pool(K)'Terminated
-- True if task Pool(K) is terminated (see 9.1)
Date'Size
-- number of bits for records of type Date (see 3.8)
Message'Address
-- address of the record variable Message (see 3.7.1)
ΓòÉΓòÉΓòÉ 7.2. Literals ΓòÉΓòÉΓòÉ
1. A literal represents a value literally, that is, by means of notation
suited to its kind. A literal is either a numeric_literal, a
character_literal, the literal null, or a string_literal.
Name Resolution Rules
2. The expected type for a literal null shall be a single access type.
3. For a name that consists of a character_literal, either its expected type
shall be a single character type, in which case it is interpreted as a
parameterless function_call that yields the corresponding value of the
character type, or its expected profile shall correspond to a
parameterless function with a character result type, in which case it is
interpreted as the name of the corresponding parameterless function
declared as part of the character type's definition, see 3.5.1. In either
case, the character_literal denotes the
enumeration_literal_specification.
4. The expected type for a primary that is a string_literal shall be a
single string type.
Legality Rules
5. A character_literal that is a name shall correspond to a
defining_character_literal of the expected type, or of the result type of
the expected profile.
6. For each character of a string_literal with a given expected string type,
there shall be a corresponding defining_character_literal of the
component type of the expected string type.
7. A literal null shall not be of an anonymous access type, since such types
do not have a null value, see 3.10.
Static Semantics
8. An integer literal is of type universal_integer. A real literal is of
type universal_real.
Dynamic Semantics
9. The evaluation of a numeric literal, or the literal null, yields the
represented value.
10. The evaluation of a string_literal that is a primary yields an array
value containing the value of each character of the sequence of
characters of the string_literal, as defined in 2.6. The bounds of this
array value are determined according to the rules for
positional_array_aggregates (see 4.3.3), except that for a null string
literal the upper bound is the predecessor of the lower bound.
11. For the evaluation of a string_literal of type T, a check is made that
the value of each character of the string_literal belongs to the
component subtype of T. For the evaluation of a null string literal, a
check is made that its lower bound is greater than the lower bound of the
base range of the index type. The exception Constraint_Error is raised if
either of these checks fails.
NOTES
12. (6) Enumeration literals that are identifiers rather than
character_literals follow the normal rules for identifiers when used in a
name, see 4.1, and 4.1.3. Character_literals used as selector_names
follow the normal rules for expanded names, see 4.1.3.
Examples
13. Examples of literals:
14.
3.14159_26536 -- a real literal
1_345 -- an integer literal
'A' -- a character literal
"Some Text" -- a string literal
ΓòÉΓòÉΓòÉ 7.3. Aggregates ΓòÉΓòÉΓòÉ
1. An aggregate combines component values into a composite value of an array
type, record type, or record extension.
Syntax
2.
aggregate ::=
record_aggregate | extension_aggregate | array_aggregate
Name Resolution Rules
3. The expected type for an aggregate shall be a single nonlimited array
type, record type, or record extension.
Legality Rules
4. An aggregate shall not be of a class-wide type.
Dynamic Semantics
5. For the evaluation of an aggregate, an anonymous object is created and
values for the components or ancestor part are obtained (as described in
the subsequent subclause for each kind of the aggregate) and assigned
into the corresponding components or ancestor part of the anonymous
object. Obtaining the values and the assignments occur in an arbitrary
order. The value of the aggregate is the value of this object.
6. If an aggregate is of a tagged type, a check is made that its value
belongs to the first subtype of the type. Constraint_Error is raised if
this check fails.
4.3.1 Record Aggregates
4.3.2 Extension Aggregates
4.3.3 Array Aggregates
ΓòÉΓòÉΓòÉ 7.3.1. Record Aggregates ΓòÉΓòÉΓòÉ
1. In a record_aggregate, a value is specified for each component of the
record or record extension value, using either a named or a positional
association.
Syntax
2.
record_aggregate ::= (record_component_association_list)
3.
record_component_association_list ::=
record_component_association {, record_component_association}
| null record
4.
record_component_association ::=
[ component_choice_list => ] expression
5.
component_choice_list ::=
component_selector_name {| component_selector_name}
| others
a. A record_component_association is a named component association if
it has a component_choice_list; otherwise, it is a positional
component association. Any positional component associations shall
precede any named component associations. If there is a named
association with a component_choice_list of others, it shall come
last.
b. In the record_component_association_list for a record_aggregate, if
there is only one association, it shall be a named association.
Name Resolution Rules
1. The expected type for a record_aggregate shall be a single nonlimited
record type or record extension.
2. For the record_component_association_list of a record_aggregate, all
components of the composite value defined by the aggregate are needed;
for the association list of an extension_aggregate, only those components
not determined by the ancestor expression or subtype are needed, see
4.3.2. Each selector_name in a record_component_association shall denote
a needed component (including possibly a discriminant).
3. The expected type for the expression of a record_component_association is
the type of the associated component(s); the associated component(s) are
as follows:
a. For a positional association, the component (including possibly a
discriminant) in the corresponding relative position (in the
declarative region of the type), counting only the needed
components;
b. For a named association with one or more component_selector_names,
the named component(s);
c. For a named association with the reserved word others, all needed
components that are not associated with some previous association.
Legality Rules
1. If the type of a record_aggregate is a record extension, then it shall be
a descendant of a record type, through one or more record extensions (and
no private extensions).
2. If there are no components needed in a given
record_component_association_list, then the reserved words null record
shall appear rather than a list of record_component_associations.
3. Each record_component_association shall have at least one associated
component, and each needed component shall be associated with exactly one
record_component_association. If a record_component_association has two
or more associated components, all of them shall be of the same type.
4. If the components of a variant_part are needed, then the value of a
discriminant that governs the variant_part shall be given by a static
expression.
Dynamic Semantics
5. The evaluation of a record_aggregate consists of the evaluation of the
record_component_association_list.
6. For the evaluation of a record_component_association_list, any per-object
constraints, see 3.8, for components specified in the association list
are elaborated and any expressions are evaluated and converted to the
subtype of the associated component. Any constraint elaborations and
expression evaluations (and conversions) occur in an arbitrary order,
except that the expression for a discriminant is evaluated (and
converted) prior to the elaboration of any per-object constraint that
depends on it, which in turn occurs prior to the evaluation and
conversion of the expression for the component with the per-object
constraint.
7. The expression of a record_component_association is evaluated (and
converted) once for each associated component.
NOTES
8. (7) For a record_aggregate with positional associations, expressions
specifying discriminant values appear first since the
known_discriminant_part is given first in the declaration of the type;
they have to be in the same order as in the known_discriminant_part.
Examples
9. Example of a record aggregate with positional associations:
10.
(4, July, 1776) -- see 3.8
11. Examples of record aggregates with named associations:
12.
(Day => 4, Month => July, Year => 1776)
(Month => July, Day => 4, Year => 1776)
13.
(Disk, Closed, Track => 5, Cylinder => 12) -- see 3.8.1
(Unit => Disk, Status => Closed, Cylinder => 9, Track => 1)
14. Example of component association with several choices:
15.
(Value => 0, Succ|Pred => new Cell'(0, null, null))
-- see 3.10.1
16.
-- The allocator is evaluated twice:
-- Succ and Pred designate different cells
17. Examples of record aggregates for tagged types, see 3.9, and 3.9.1
18.
Expression'(null record)
Literal'(Value => 0.0)
Painted_Point'(0.0, Pi/2.0, Paint => Red)
ΓòÉΓòÉΓòÉ 7.3.2. Extension Aggregates ΓòÉΓòÉΓòÉ
1. An extension_aggregate specifies a value for a type that is a record
extension by specifying a value or subtype for an ancestor of the type,
followed by associations for any components not determined by the
ancestor_part.
Syntax
2.
extension_aggregate ::=
(ancestor_part with record_component_association_list)
3.
ancestor_part ::= expression | subtype_mark
Name Resolution Rules
4. The expected type for an extension_aggregate shall be a single nonlimited
type that is a record extension. If the ancestor_part is an expression,
it is expected to be of any nonlimited tagged type.
Legality Rules
5. If the ancestor_part is a subtype_mark, it shall denote a specific tagged
subtype. The type of the extension_aggregate shall be derived from the
type of the ancestor_part, through one or more record extensions (and no
private extensions).
Static Semantics
6. For the record_component_association_list of an extension_aggregate, the
only components needed are those of the composite value defined by the
aggregate that are not inherited from the type of the ancestor_part, plus
any inherited discriminants if the ancestor_part is a subtype_mark that
denotes an unconstrained subtype.
Dynamic Semantics
7. For the evaluation of an extension_aggregate, the
record_component_association_list is evaluated. If the ancestor_part is
an expression, it is also evaluated; if the ancestor_part is a
subtype_mark, the components of the value of the aggregate not given by
the record_component_association_list are initialized by default as for
an object of the ancestor type. Any implicit initializations or
evaluations are performed in an arbitrary order, except that the
expression for a discriminant is evaluated prior to any other evaluation
or initialization that depends on it.
8. If the type of the ancestor_part has discriminants that are not inherited
by the type of the extension_aggregate, then, unless the ancestor_part is
a subtype_mark that denotes an unconstrained subtype, a check is made
that each discriminant of the ancestor has the value specified for a
corresponding discriminant, either in the
record_component_association_list, or in the derived_type_definition for
some ancestor of the type of the extension_aggregate. Constraint_Error is
raised if this check fails.
NOTES
9. (8) If all components of the value of the extension_aggregate are
determined by the ancestor_part, then the
record_component_association_list is required to be simply null record.
10. (9) If the ancestor_part is a subtype_mark, then its type can be
abstract. If its type is controlled, then as the last step of evaluating
the aggregate, the Initialize procedure of the ancestor type is called,
unless the Initialize procedure is abstract, see 7.6.
Examples
11. Examples of extension aggregates (for types defined in 3.9.1.):
12.
Painted_Point'(Point with Red)
(Point'(P) with Paint => Black)
13.
(Expression with Left => 1.2, Right => 3.4)
Addition'(Binop with null record)
-- presuming Binop is of type Binary_Operation
ΓòÉΓòÉΓòÉ 7.3.3. Array Aggregates ΓòÉΓòÉΓòÉ
1. In an array_aggregate, a value is specified for each component of an
array, either positionally or by its index. For a
positional_array_aggregate, the components are given in increasing-index
order, with a final others, if any, representing any remaining
components. For a named_array_aggregate, the components are identified by
the values covered by the discrete_choices.
Syntax
2.
array_aggregate ::=
positional_array_aggregate | named_array_aggregate
3.
positional_array_aggregate ::=
(expression, expression {, expression})
| (expression {, expression}, others => expression)
4.
named_array_aggregate ::=
(array_component_association {, array_component_association})
5.
array_component_association ::=
discrete_choice_list => expression
6. An n-dimensional array_aggregate is one that is written as n levels of
nested array_aggregates (or at the bottom level, equivalent
string_literals). For the multidimensional case (n >= 2) the
array_aggregates (or equivalent string_literals) at the n-1 lower levels
are called subaggregates of the enclosing n-dimensional array_aggregate.
The expressions of the bottom level subaggregates (or of the
array_aggregate itself if one-dimensional) are called the array component
expressions of the enclosing n-dimensional array_aggregate.
Name Resolution Rules
7. The expected type for an array_aggregate (that is not a subaggregate)
shall be a single nonlimited array type. The component type of this array
type is the expected type for each array component expression of the
array_aggregate.
8. The expected type for each discrete_choice in any discrete_choice_list of
a named_array_aggregate is the type of the corresponding index; the
corresponding index for an array_aggregate that is not a subaggregate is
the first index of its type; for an (n-m)-dimensional subaggregate within
an array_aggregate of an n-dimensional type, the corresponding index is
the index in position m+1.
Legality Rules
9. An array_aggregate of an n-dimensional array type shall be written as an
n-dimensional array_aggregate.
10. An others choice is allowed for an array_aggregate only if an applicable
index constraint applies to the array_aggregate. An applicable index
constraint is a constraint provided by certain contexts where an
array_aggregate is permitted that can be used to determine the bounds of
the array value specified by the aggregate. Each of the following
contexts (and none other) defines an applicable index constraint:
a. For an explicit_actual_parameter, an
explicit_generic_actual_parameter, the expression of a
return_statement, the initialization expression in an
object_declaration, or a default_expression (for a parameter or a
component), when the nominal subtype of the corresponding formal
parameter, generic formal parameter, function result, object, or
component is a constrained array subtype, the applicable index
constraint is the constraint of the subtype;
b. For the expression of an assignment_statement where the name denotes
an array variable, the applicable index constraint is the constraint
of the array variable;
c. For the operand of a qualified_expression whose subtype_mark denotes
a constrained array subtype, the applicable index constraint is the
constraint of the subtype;
d. For a component expression in an aggregate, if the component's
nominal subtype is a constrained array subtype, the applicable index
constraint is the constraint of the subtype;
e. For a parenthesized expression, the applicable index constraint is
that, if any, defined for the expression.
1. The applicable index constraint applies to an array_aggregate that
appears in such a context, as well as to any subaggregates thereof. In
the case of an explicit_actual_parameter (or default_expression) for a
call on a generic formal subprogram, no applicable index constraint is
defined.
2. The discrete_choice_list of an array_component_association is allowed to
have a discrete_choice that is a nonstatic expression or that is a
discrete_range that defines a nonstatic or null range, only if it is the
single discrete_choice of its discrete_choice_list, and there is only one
array_component_association in the array_aggregate.
3. In a named_array_aggregate with more than one discrete_choice, no two
discrete_choices are allowed to cover the same value, see 3.8.1, if there
is no others choice, the discrete_choices taken together shall exactly
cover a contiguous sequence of values of the corresponding index type.
4. A bottom level subaggregate of a multidimensional array_aggregate of a
given array type is allowed to be a string_literal only if the component
type of the array type is a character type; each character of such a
string_literal shall correspond to a defining_character_literal of the
component type.
Static Semantics
5. A subaggregate that is a string_literal is equivalent to one that is a
positional_array_aggregate of the same length, with each expression being
the character_literal for the corresponding character of the
string_literal.
Dynamic Semantics
6. The evaluation of an array_aggregate of a given array type proceeds in
two steps:
a. Any discrete_choices of this aggregate and of its subaggregates are
evaluated in an arbitrary order, and converted to the corresponding
index type;
b. The array component expressions of the aggregate are evaluated in an
arbitrary order and their values are converted to the component
subtype of the array type; an array component expression is
evaluated once for each associated component.
1. The bounds of the index range of an array_aggregate (including a
subaggregate) are determined as follows:
a. For an array_aggregate with an others choice, the bounds are those
of the corresponding index range from the applicable index
constraint;
b. For a positional_array_aggregate (or equivalent string_literal)
without an others choice, the lower bound is that of the
corresponding index range in the applicable index constraint, if
defined, or that of the corresponding index subtype, if not; in
either case, the upper bound is determined from the lower bound and
the number of expressions (or the length of the string_literal);
c. For a named_array_aggregate without an others choice, the bounds are
determined by the smallest and largest index values covered by any
discrete_choice_list.
1. For an array_aggregate, a check is made that the index range defined by
its bounds is compatible with the corresponding index subtype.
2. For an array_aggregate with an others choice, a check is made that no
expression is specified for an index value outside the bounds determined
by the applicable index constraint.
3. For a multidimensional array_aggregate, a check is made that all
subaggregates that correspond to the same index have the same bounds.
4. The exception Constraint_Error is raised if any of the above checks fail.
NOTES
5. (10) In an array_aggregate, positional notation may only be used with two
or more expressions; a single expression in parentheses is interpreted as
a parenthesized_expression. A named_array_aggregate, such as (1 => X),
may be used to specify an array with a single component.
Examples
6. Examples of array aggregates with positional associations:
7.
(7, 9, 5, 1, 3, 2, 4, 8, 6, 0)
Table'(5, 8, 4, 1, others => 0) -- see 3.6
8. Examples of array aggregates with named associations:
9.
(1 ┬╖┬╖ 5 => (1 ┬╖┬╖ 8 => 0.0)) -- two-dimensional
(1 ┬╖┬╖ N => new Cell) -- N new cells, in particular for N = 0
10.
Table'(2 | 4 | 10 => 1, others => 0)
Schedule'(Mon ┬╖┬╖ Fri => True, others => False)
Schedule'(Wed | Sun => False, others => True)
-- see 3.6
Vector'(1 => 2.5)
-- single-component vector
11. Examples of two-dimensional array aggregates:
12.
-- Three aggregates for the same value of subtype
-- Matrix(1┬╖┬╖2,1┬╖┬╖3), see 3.6
13.
((1.1, 1.2, 1.3), (2.1, 2.2, 2.3))
(1 => (1.1, 1.2, 1.3), 2 => (2.1, 2.2, 2.3))
(1 => (1 => 1.1, 2 => 1.2, 3 => 1.3),
2 => (1 => 2.1, 2 => 2.2, 3 => 2.3))
14. Examples of aggregates as initial values:
15.
A : Table := (7, 9, 5, 1, 3, 2, 4, 8, 6, 0);
-- A(1)=7, A(10)=0
B : Table := (2 | 4 | 10 => 1, others => 0);
-- B(1)=0, B(10)=1
C : constant Matrix := (1 ┬╖┬╖ 5 => (1 ┬╖┬╖ 8 => 0.0));
-- C'Last(1)=5, C'Last(2)=8
16.
D : Bit_Vector(M ┬╖┬╖ N) := (M ┬╖┬╖ N => True); -- see 3.6
E : Bit_Vector(M ┬╖┬╖ N) := (others => True);
F : String(1 ┬╖┬╖ 1) := (1 => 'F');
-- a one component aggregate: same as "F"
ΓòÉΓòÉΓòÉ 7.4. Expressions ΓòÉΓòÉΓòÉ
1. An expression is a formula that defines the computation or retrieval of a
value. In this International Standard, the term ``expression'' refers to
a construct of the syntactic category expression or of any of the other
five syntactic categories defined below.
Syntax
2.
expression ::=
relation {and relation} | relation {and then relation}
| relation {or relation} | relation {or else relation}
| relation {xor relation}
3.
relation ::=
simple_expression [relational_operator simple_expression]
| simple_expression [not] in range
| simple_expression [not] in subtype_mark
4.
simple_expression ::=
[unary_adding_operator] term {binary_adding_operator term}
5.
term ::= factor {multiplying_operator factor}
6.
factor ::= primary [** primary] | abs primary | not primary
7.
primary ::=
numeric_literal | null
| string_literal | aggregate
| name | qualified_expression
| allocator | (expression)
Name Resolution Rules
8. A name used as a primary shall resolve to denote an object or a value.
Static Semantics
9. Each expression has a type; it specifies the computation or retrieval of
a value of that type.
Dynamic Semantics
10. The value of a primary that is a name denoting an object is the value of
the object.
Implementation Permissions
11. For the evaluation of a primary that is a name denoting an object of an
unconstrained numeric subtype, if the value of the object is outside the
base range of its type, the implementation may either raise
Constraint_Error or return the value of the object.
Examples
12. Examples of primaries:
13.
4.0 -- real literal
Pi -- named number
(1 ┬╖┬╖ 10 => 0) -- array aggregate
Sum -- variable
Integer'Last -- attribute
Sine(X) -- function call
Color'(Blue) -- qualified expression
Real(M*N) -- conversion
(Line_Count + 10) -- parenthesized expression
14. Examples of expressions:
15.
Volume -- primary
not Destroyed -- factor
2*Line_Count -- term
-4.0 -- simple expression
-4.0 + A -- simple expression
B**2 - 4.0*A*C -- simple expression
Password(1 ┬╖┬╖ 3) = "Bwv" -- relation
Count in Small_Int -- relation
Count not in Small_Int -- relation
Index = 0 or Item_Hit -- expression
(Cold and Sunny) or Warm -- expression (parentheses are required)
A**(B**C) -- expression (parentheses are required)
ΓòÉΓòÉΓòÉ 7.5. Operators and Expression Evaluation ΓòÉΓòÉΓòÉ
1. The language defines the following six categories of operators (given in
order of increasing precedence). The corresponding operator_symbols, and
only those, can be used as designators in declarations of functions for
user-defined operators (see 6.6: ``Overloading of Operators'').
Syntax
2.
logical_operator ::= and | or | xor
3.
relational_operator ::= = | /= | < | <= | > | >=
4.
binary_adding_operator ::= + | - | &
5.
unary_adding_operator ::= + | -
6.
multiplying_operator ::= * | / | mod | rem
7.
highest_precedence_operator ::= ** | abs | not
Static Semantics
8. For a sequence of operators of the same precedence level, the operators
are associated with their operands in textual order from left to right.
Parentheses can be used to impose specific associations.
9. For each form of type definition, certain of the above operators are
predefined; that is, they are implicitly declared immediately after the
type definition. For each such implicit operator declaration, the
parameters are called Left and Right for binary operators; the single
parameter is called Right for unary operators. An expression of the form
X op Y, where op is a binary operator, is equivalent to a function_call
of the form "op"(X, Y). An expression of the form op Y, where op is a
unary operator, is equivalent to a function_call of the form "op"(Y). The
predefined operators and their effects are described in subclauses 4.5.1
through 4.5.6.
Dynamic Semantics
10. The predefined operations on integer types either yield the
mathematically correct result or raise the exception Constraint_Error.
For implementations that support the Numerics Annex, the predefined
operations on real types yield results whose accuracy is defined in G:
``Annex G'', or raise the exception Constraint_Error.
Implementation Requirements
11. The implementation of a predefined operator that delivers a result of an
integer or fixed point type may raise Constraint_Error only if the result
is outside the base range of the result type.
12. The implementation of a predefined operator that delivers a result of a
floating point type may raise Constraint_Error only if the result is
outside the safe range of the result type.
Implementation Permissions
13. For a sequence of predefined operators of the same precedence level (and
in the absence of parentheses imposing a specific association), an
implementation may impose any association of the operators with operands
so long as the result produced is an allowed result for the left-to-right
association, but ignoring the potential for failure of language-defined
checks in either the left-to-right or chosen order of association.
NOTES
14. (11) The two operands of an expression of the form X op Y, where op is a
binary operator, are evaluated in an arbitrary order, as for any
function_call, see 6.4.
Examples
15. Examples of precedence:
16.
not Sunny or Warm -- same as (not Sunny) or Warm
X > 4.0 and Y > 0.0 -- same as (X > 4.0) and (Y > 0.0)
17.
-4.0*A**2 -- same as -(4.0 * (A**2))
abs(1 + A) + B -- same as (abs (1 + A)) + B
Y**(-3) -- parentheses are necessary
A / B * C -- same as (A/B)*C
A + (B + C) -- evaluate B + C before adding it to A
4.5.1 Logical Operators and Short-circuit Control
Forms
4.5.2 Relational Operators and Membership Tests
4.5.3 Binary Adding Operators
4.5.4 Unary Adding Operators
4.5.5 Multiplying Operators
4.5.6 Highest Precedence Operators
ΓòÉΓòÉΓòÉ 7.5.1. Logical Operators and Short-circuit Control Forms ΓòÉΓòÉΓòÉ
Name Resolution Rules
1. An expression consisting of two relations connected by and then or or
else (a short-circuit control form) shall resolve to be of some boolean
type; the expected type for both relations is that same boolean type.
Static Semantics
2. The following logical operators are predefined for every boolean type T,
for every modular type T, and for every one-dimensional array type T
whose component type is a boolean type:
3.
function "and"(Left, Right : T) return T
function "or" (Left, Right : T) return T
function "xor"(Left, Right : T) return T
4. For boolean types, the predefined logical operators and, or, and xor
perform the conventional operations of conjunction, inclusive
disjunction, and exclusive disjunction, respectively.
5. For modular types, the predefined logical operators are defined on a
bit-by-bit basis, using the binary representation of the value of the
operands to yield a binary representation for the result, where zero
represents False and one represents True. If this result is outside the
base range of the type, a final subtraction by the modulus is performed
to bring the result into the base range of the type.
6. The logical operators on arrays are performed on a component-by-component
basis on matching components (as for equality -- see 4.5.2.), using the
predefined logical operator for the component type. The bounds of the
resulting array are those of the left operand.
Dynamic Semantics
7. The short-circuit control forms and then and or else deliver the same
result as the corresponding predefined and and or operators for boolean
types, except that the left operand is always evaluated first, and the
right operand is not evaluated if the value of the left operand
determines the result.
8. For the logical operators on arrays, a check is made that for each
component of the left operand there is a matching component of the right
operand, and vice versa. Also, a check is made that each component of the
result belongs to the component subtype. The exception Constraint_Error
is raised if either of the above checks fails.
NOTES
9. (12) The conventional meaning of the logical operators is given by the
following truth table:
10.
A B (A and B) (A or B) (A xor B)
True True True True False
True False False True True
False True False True True
False False False False False
Examples
11. Examples of logical operators:
12.
Sunny or Warm
Filter(1 ┬╖┬╖ 10) and Filter(15 ┬╖┬╖ 24) -- see 3.6.1
13. Examples of short-circuit control forms:
14.
Next_Car.Owner /= null and then Next_Car.Owner.Age > 25
-- see 3.10.1
N = 0 or else A(N) = Hit_Value
ΓòÉΓòÉΓòÉ 7.5.2. Relational Operators and Membership Tests ΓòÉΓòÉΓòÉ
1. The equality operators = (equals) and /= (not equals) are predefined for
nonlimited types. The other relational_operators are the ordering
operators < (less than), <= (less than or equal), > (greater than), and
>= (greater than or equal). The ordering operators are predefined for
scalar types, and for discrete array types, that is, one-dimensional
array types whose components are of a discrete type.
2. A membership test, using in or not in, determines whether or not a value
belongs to a given subtype or range, or has a tag that identifies a type
that is covered by a given type. Membership tests are allowed for all
types.
Name Resolution Rules
3. The tested type of a membership test is the type of the range or the type
determined by the subtype_mark. If the tested type is tagged, then the
simple_expression shall resolve to be of a type that covers or is covered
by the tested type; if untagged, the expected type for the
simple_expression is the tested type.
Legality Rules
4. For a membership test, if the simple_expression is of a tagged class-wide
type, then the tested type shall be (visibly) tagged.
Static Semantics
5. The result type of a membership test is the predefined type Boolean.
6. The equality operators are predefined for every specific type T that is
not limited, and not an anonymous access type, with the following
specifications:
7.
function "=" (Left, Right : T) return Boolean
function "/="(Left, Right : T) return Boolean
8. The ordering operators are predefined for every specific scalar type T,
and for every discrete array type T, with the following specifications:
9.
function "<" (Left, Right : T) return Boolean
function "<="(Left, Right : T) return Boolean
function ">" (Left, Right : T) return Boolean
function ">="(Left, Right : T) return Boolean
Dynamic Semantics
10. For discrete types, the predefined relational operators are defined in
terms of corresponding mathematical operations on the position numbers of
the values of the operands.
11. For real types, the predefined relational operators are defined in terms
of the corresponding mathematical operations on the values of the
operands, subject to the accuracy of the type.
12. Two access-to-object values are equal if they designate the same object,
or if both are equal to the null value of the access type.
13. Two access-to-subprogram values are equal if they are the result of the
same evaluation of an Access attribute_reference, or if both are equal to
the null value of the access type. Two access-to-subprogram values are
unequal if they designate different subprograms. It is unspecified
whether two access values that designate the same subprogram but are the
result of distinct evaluations of Access attribute_references are equal
or unequal.
14. For a type extension, predefined equality is defined in terms of the
primitive (possibly user-defined) equals operator of the parent type and
of any tagged components of the extension part, and predefined equality
for any other components not inherited from the parent type.
15. For a private type, if its full type is tagged, predefined equality is
defined in terms of the primitive equals operator of the full type; if
the full type is untagged, predefined equality for the private type is
that of its full type.
16. For other composite types, the predefined equality operators (and certain
other predefined operations on composite types -- see 4.5.1, and 4.6.)
are defined in terms of the corresponding operation on matching
components, defined as follows:
a. For two composite objects or values of the same non-array type,
matching components are those that correspond to the same
component_declaration or discriminant_specification;
b. For two one-dimensional arrays of the same type, matching components
are those (if any) whose index values match in the following sense:
the lower bounds of the index ranges are defined to match, and the
successors of matching indices are defined to match;
c. For two multidimensional arrays of the same type, matching
components are those whose index values match in successive index
positions.
1. The analogous definitions apply if the types of the two objects or values
are convertible, rather than being the same.
2. Given the above definition of matching components, the result of the
predefined equals operator for composite types (other than for those
composite types covered earlier) is defined as follows:
a. If there are no components, the result is defined to be True;
b. If there are unmatched components, the result is defined to be
False;
c. Otherwise, the result is defined in terms of the primitive equals
operator for any matching tagged components, and the predefined
equals for any matching untagged components.
1. The predefined "/=" operator gives the complementary result to the
predefined "=" operator.
2. For a discrete array type, the predefined ordering operators correspond
to lexicographic order using the predefined order relation of the
component type: A null array is lexicographically less than any array
having at least one component. In the case of nonnull arrays, the left
operand is lexicographically less than the right operand if the first
component of the left operand is less than that of the right; otherwise
the left operand is lexicographically less than the right operand only if
their first components are equal and the tail of the left operand is
lexicographically less than that of the right (the tail consists of the
remaining components beyond the first and can be null).
3. For the evaluation of a membership test, the simple_expression and the
range (if any) are evaluated in an arbitrary order.
4. A membership test using in yields the result True if:
a. The tested type is scalar, and the value of the simple_expression
belongs to the given range, or the range of the named subtype; or
b. The tested type is not scalar, and the value of the simple_
expression satisfies any constraints of the named subtype, and, if
the type of the simple_expression is class-wide, the value has a tag
that identifies a type covered by the tested type.
1. Otherwise the test yields the result False.
2. A membership test using not in gives the complementary result to the
corresponding membership test using in.
NOTES
3. (13) No exception is ever raised by a membership test, by a predefined
ordering operator, or by a predefined equality operator for an elementary
type, but an exception can be raised by the evaluation of the operands. A
predefined equality operator for a composite type can only raise an
exception if the type has a tagged part whose primitive equals operator
propagates an exception.
4. (14) If a composite type has components that depend on discriminants, two
values of this type have matching components if and only if their
discriminants are equal. Two nonnull arrays have matching components if
and only if the length of each dimension is the same for both.
Examples
5. Examples of expressions involving relational operators and membership
tests:
6.
X /= Y
7.
"" < "A" and "A" < "Aa" -- True
"Aa" < "B" and "A" < "A " -- True
8.
My_Car = null
-- true if My_Car has been set to null (see 3.10.1)
My_Car = Your_Car
-- true if we both share the same car
My_Car.all = Your_Car.all
-- true if the two cars are identical
9.
N not in 1 ┬╖┬╖ 10
-- range membership test
Today in Mon ┬╖┬╖ Fri
-- range membership test
Today in Weekday
-- subtype membership test (see 3.5.1)
Archive in Disk_Unit
-- subtype membership test, see 3.8.1
Tree.all in Addition'Class
-- class membership test (see 3.9.1)
ΓòÉΓòÉΓòÉ 7.5.3. Binary Adding Operators ΓòÉΓòÉΓòÉ
Static Semantics
1. The binary adding operators + (addition) and - (subtraction) are
predefined for every specific numeric type T with their conventional
meaning. They have the following specifications:
2.
function "+"(Left, Right : T) return T
function "-"(Left, Right : T) return T
3. The concatenation operators & are predefined for every nonlimited,
one-dimensional array type T with component type C. They have the
following specifications:
4.
function "&"(Left : T; Right : T) return T
function "&"(Left : T; Right : C) return T
function "&"(Left : C; Right : T) return T
function "&"(Left : C; Right : C) return T
Dynamic Semantics
5. For the evaluation of a concatenation with result type T, if both
operands are of type T, the result of the concatenation is a
one-dimensional array whose length is the sum of the lengths of its
operands, and whose components comprise the components of the left
operand followed by the components of the right operand. If the left
operand is a null array, the result of the concatenation is the right
operand. Otherwise, the lower bound of the result is determined as
follows:
a. If the ultimate ancestor of the array type was defined by a
constrained_array_definition, then the lower bound of the result is
that of the index subtype;
b. If the ultimate ancestor of the array type was defined by an
unconstrained_array_definition, then the lower bound of the result
is that of the left operand.
1. The upper bound is determined by the lower bound and the length. A check
is made that the upper bound of the result of the concatenation belongs
to the range of the index subtype, unless the result is a null array.
Constraint_Error is raised if this check fails.
2. If either operand is of the component type C, the result of the
concatenation is given by the above rules, using in place of such an
operand an array having this operand as its only component (converted to
the component subtype) and having the lower bound of the index subtype of
the array type as its lower bound.
3. The result of a concatenation is defined in terms of an assignment to an
anonymous object, as for any function call, see 6.5.
NOTES
4. (15) As for all predefined operators on modular types, the binary adding
operators + and - on modular types include a final reduction modulo the
modulus if the result is outside the base range of the type.
Examples
5. Examples of expressions involving binary adding operators:
6.
Z + 0.1
-- Z has to be of a real type
7.
"A" & "BCD"
-- concatenation of two string literals
'A' & "BCD"
-- concatenation of a character literal and a string literal
'A' & 'A'
-- concatenation of two character literals
ΓòÉΓòÉΓòÉ 7.5.4. Unary Adding Operators ΓòÉΓòÉΓòÉ
Static Semantics
1. The unary adding operators + (identity) and - (negation) are predefined
for every specific numeric type T with their conventional meaning. They
have the following specifications:
2.
function "+"(Right : T) return T
function "-"(Right : T) return T
NOTES
3. (16) For modular integer types, the unary adding operator -, when given a
nonzero operand, returns the result of subtracting the value of the
operand from the modulus; for a zero operand, the result is zero.
ΓòÉΓòÉΓòÉ 7.5.5. Multiplying Operators ΓòÉΓòÉΓòÉ
Static Semantics
1. The multiplying operators * (multiplication), / (division), mod
(modulus), and rem (remainder) are predefined for every specific integer
type T:
2.
function "*" (Left, Right : T) return T
function "/" (Left, Right : T) return T
function "mod"(Left, Right : T) return T
function "rem"(Left, Right : T) return T
3. Signed integer multiplication has its conventional meaning.
4. Signed integer division and remainder are defined by the relation:
5.
A = (A/B)*B + (A rem B)
6. where (A rem B) has the sign of A and an absolute value less than the
absolute value of B. Signed integer division satisfies the identity:
7.
(-A)/B = -(A/B) = A/(-B)
8. The signed integer modulus operator is defined such that the result of A
mod B has the sign of B and an absolute value less than the absolute
value of B; in addition, for some signed integer value N, this result
satisfies the relation:
9.
A = B*N + (A mod B)
10. The multiplying operators on modular types are defined in terms of the
corresponding signed integer operators, followed by a reduction modulo
the modulus if the result is outside the base range of the type (which is
only possible for the "*" operator).
11. Multiplication and division operators are predefined for every specific
floating point type T:
12.
function "*"(Left, Right : T) return T
function "/"(Left, Right : T) return T
13. The following multiplication and division operators, with an operand of
the predefined type Integer, are predefined for every specific fixed
point type T:
14.
function "*"(Left : T; Right : Integer) return T
function "*"(Left : Integer; Right : T) return T
function "/"(Left : T; Right : Integer) return T
15. All of the above multiplying operators are usable with an operand of an
appropriate universal numeric type. The following additional multiplying
operators for root_real are predefined, and are usable when both operands
are of an appropriate universal or root numeric type, and the result is
allowed to be of type root_real, as in a number_declaration:
16.
function "*"(Left, Right : root_real) return root_real
function "/"(Left, Right : root_real) return root_real
17.
function "*"(Left : root_real; Right : root_integer) return root_real
function "*"(Left : root_integer; Right : root_real) return root_real
function "/"(Left : root_real; Right : root_integer) return root_real
18. Multiplication and division between any two fixed point types are
provided by the following two predefined operators:
19.
function "*"(Left, Right : universal_fixed) return universal_fixed
function "/"(Left, Right : universal_fixed) return universal_fixed
Legality Rules
20. The above two fixed-fixed multiplying operators shall not be used in a
context where the expected type for the result is itself universal_fixed
-- the context has to identify some other numeric type to which the
result is to be converted, either explicitly or implicitly.
Dynamic Semantics
21. The multiplication and division operators for real types have their
conventional meaning. For floating point types, the accuracy of the
result is determined by the precision of the result type. For decimal
fixed point types, the result is truncated toward zero if the
mathematical result is between two multiples of the small of the specific
result type (possibly determined by context); for ordinary fixed point
types, if the mathematical result is between two multiples of the small,
it is unspecified which of the two is the result.
22. The exception Constraint_Error is raised by integer division, rem, and
mod if the right operand is zero. Similarly, for a real type T with
T'Machine_Overflows True, division by zero raises Constraint_Error.
NOTES
23. (17) For positive A and B, A/B is the quotient and A rem B is the
remainder when A is divided by B. The following relations are satisfied
by the rem operator:
24.
A rem (-B) = A rem B
(-A) rem B = -(A rem B)
25. (18) For any signed integer K, the following identity holds:
26.
A mod B = (A + K*B) mod B
27. The relations between signed integer division, remainder, and modulus are
illustrated by the following table:
28.
A B A/B A rem B A mod B A B A/B A rem B A mod B
29.
10 5 2 0 0 -10 5 -2 0 0
11 5 2 1 1 -11 5 -2 -1 4
12 5 2 2 2 -12 5 -2 -2 3
13 5 2 3 3 -13 5 -2 -3 2
14 5 2 4 4 -14 5 -2 -4 1
30.
A B A/B A rem B A mod B A B A/B A rem B A mod B
10 -5 -2 0 0 -10 -5 2 0 0
11 -5 -2 1 -4 -11 -5 2 -1 -1
12 -5 -2 2 -3 -12 -5 2 -2 -2
13 -5 -2 3 -2 -13 -5 2 -3 -3
14 -5 -2 4 -1 -14 -5 2 -4 -4
Examples
31. Examples of expressions involving multiplying operators:
32.
I : Integer := 1;
J : Integer := 2;
K : Integer := 3;
33.
X : Real := 1.0; -- see 3.5.7
Y : Real := 2.0;
34.
F : Fraction := 0.25; -- see 3.5.9
G : Fraction := 0.5;
35.
Expression Value Result Type
I*J 2 same as I and J, that is, Integer
K/J 1 same as K and J, that is, Integer
K mod J 1 same as K and J, that is, Integer
X/Y 0.5 same as X and Y, that is, Real
F/2 0.125 same as F, that is, Fraction
3*F 0.75 same as F, that is, Fraction
0.75*G 0.375 universal_fixed, implicitly convertible
to any fixed point type
Fraction(F*G) 0.125 Fraction, as stated by the conversion
Real(J)*Y 4.0 Real, the type of both operands after
conversion of J
ΓòÉΓòÉΓòÉ 7.5.6. Highest Precedence Operators ΓòÉΓòÉΓòÉ
Static Semantics
1. The highest precedence unary operator abs (absolute value) is predefined
for every specific numeric type T, with the following specification:
2.
function "abs"(Right : T) return T
3. The highest precedence unary operator not (logical negation) is
predefined for every boolean type T, every modular type T, and for every
one-dimensional array type T whose components are of a boolean type, with
the following specification:
4.
function "not"(Right : T) return T
5. The result of the operator not for a modular type is defined as the
difference between the high bound of the base range of the type and the
value of the operand. For a binary modulus, this corresponds to a
bit-wise complement of the binary representation of the value of the
operand.
6. The operator not that applies to a one-dimensional array of boolean
components yields a one-dimensional boolean array with the same bounds;
each component of the result is obtained by logical negation of the
corresponding component of the operand (that is, the component that has
the same index value). A check is made that each component of the result
belongs to the component subtype; the exception Constraint_Error is
raised if this check fails.
7. The highest precedence exponentiation operator ** is predefined for every
specific integer type T with the following specification:
8.
function "**"(Left : T; Right : Natural) return T
9. Exponentiation is also predefined for every specific floating point type
as well as root_real, with the following specification (where T is
root_real or the floating point type):
10.
function "**"(Left : T; Right : Integer'Base) return T
11. The right operand of an exponentiation is the exponent. The expression
X**N with the value of the exponent N positive is equivalent to the
expression X*X*┬╖┬╖┬╖X (with N-1 multiplications) except that the
multiplications are associated in an arbitrary order. With N equal to
zero, the result is one. With the value of N negative (only defined for a
floating point operand), the result is the reciprocal of the result using
the absolute value of N as the exponent.
Implementation Permissions
12. The implementation of exponentiation for the case of a negative exponent
is allowed to raise Constraint_Error if the intermediate result of the
repeated multiplications is outside the safe range of the type, even
though the final result (after taking the reciprocal) would not be. (The
best machine approximation to the final result in this case would
generally be 0.0.)
NOTES
13. (19) As implied by the specification given above for exponentiation of an
integer type, a check is made that the exponent is not negative.
Constraint_Error is raised if this check fails.
ΓòÉΓòÉΓòÉ 7.6. Type Conversions ΓòÉΓòÉΓòÉ
1. Explicit type conversions, both value conversions and view conversions,
are allowed between closely related types as defined below. This clause
also defines rules for value and view conversions to a particular subtype
of a type, both explicit ones and those implicit in other constructs.
Syntax
2.
type_conversion ::=
subtype_mark(expression)
| subtype_mark(name)
3. The target subtype of a type_conversion is the subtype denoted by the
subtype_mark. The operand of a type_conversion is the expression or name
within the parentheses; its type is the operand type.
4. One type is convertible to a second type if a type_conversion with the
first type as operand type and the second type as target type is legal
according to the rules of this clause. Two types are convertible if each
is convertible to the other.
5. A type_conversion whose operand is the name of an object is called a view
conversion if its target type is tagged, or if it appears as an actual
parameter of mode out or in out; other type_conversions are called value
conversions.
Name Resolution Rules
6. The operand of a type_conversion is expected to be of any type.
7. The operand of a view conversion is interpreted only as a name; the
operand of a value conversion is interpreted as an expression.
Legality Rules
8. If the target type is a numeric type, then the operand type shall be a
numeric type.
9. If the target type is an array type, then the operand type shall be an
array type. Further:
a. The types shall have the same dimensionality;
b. Corresponding index types shall be convertible; and
c. The component subtypes shall statically match.
1. If the target type is a general access type, then the operand type shall
be an access-to-object type. Further:
a. If the target type is an access-to-variable type, then the operand
type shall be an access-to-variable type;
b. If the target designated type is tagged, then the operand designated
type shall be convertible to the target designated type;
c. If the target designated type is not tagged, then the designated
types shall be the same, and either the designated subtypes shall
statically match or the target designated subtype shall be
discriminated and unconstrained; and
d. The accessibility level of the operand type shall not be statically
deeper than that of the target type. In addition to the places where
Legality Rules normally apply, see 12.3, this rule applies also in
the private part of an instance of a generic unit.
1. If the target type is an access-to-subprogram type, then the operand type
shall be an access-to-subprogram type. Further:
a. The designated profiles shall be subtype-conformant.
b. The accessibility level of the operand type shall not be statically
deeper than that of the target type. In addition to the places where
Legality Rules normally apply, see 12.3, this rule applies also in
the private part of an instance of a generic unit. If the operand
type is declared within a generic body, the target type shall be
declared within the generic body.
1. If the target type is not included in any of the above four cases, there
shall be a type that is an ancestor of both the target type and the
operand type. Further, if the target type is tagged, then either:
a. The operand type shall be covered by or descended from the target
type; or
b. The operand type shall be a class-wide type that covers the target
type.
1. In a view conversion for an untagged type, the target type shall be
convertible (back) to the operand type.
Static Semantics
2. A type_conversion that is a value conversion denotes the value that is
the result of converting the value of the operand to the target subtype.
3. A type_conversion that is a view conversion denotes a view of the object
denoted by the operand. This view is a variable of the target type if the
operand denotes a variable; otherwise it is a constant of the target
type.
4. The nominal subtype of a type_conversion is its target subtype.
Dynamic Semantics
5. For the evaluation of a type_conversion that is a value conversion, the
operand is evaluated, and then the value of the operand is converted to a
corresponding value of the target type, if any. If there is no value of
the target type that corresponds to the operand value, Constraint_Error
is raised; this can only happen on conversion to a modular type, and only
when the operand value is outside the base range of the modular type.
Additional rules follow:
a. Numeric Type Conversion
1. If the target and the operand types are both integer types,
then the result is the value of the target type that
corresponds to the same mathematical integer as the operand.
2. If the target type is a decimal fixed point type, then the
result is truncated (toward 0) if the value of the operand is
not a multiple of the small of the target type.
3. If the target type is some other real type, then the result is
within the accuracy of the target type (see G.2: ``Numeric
Performance Requirements'', for implementations that support
the Numerics Annex).
4. If the target type is an integer type and the operand type is
real, the result is rounded to the nearest integer (away from
zero if exactly halfway between two integers).
a. Enumeration Type Conversion
1. The result is the value of the target type with the same
position number as that of the operand value.
a. Array Type Conversion
1. If the target subtype is a constrained array subtype, then a
check is made that the length of each dimension of the value of
the operand equals the length of the corresponding dimension of
the target subtype. The bounds of the result are those of the
target subtype.
2. If the target subtype is an unconstrained array subtype, then
the bounds of the result are obtained by converting each bound
of the value of the operand to the corresponding index type of
the target type. For each nonnull index range, a check is made
that the bounds of the range belong to the corresponding index
subtype.
3. In either array case, the value of each component of the result
is that of the matching component of the operand value, see
4.5.2.
a. Composite (Non-Array) Type Conversion
1. The value of each nondiscriminant component of the result is
that of the matching component of the operand value.
2. The tag of the result is that of the operand. If the operand
type is class-wide, a check is made that the tag of the operand
identifies a (specific) type that is covered by or descended
from the target type.
3. For each discriminant of the target type that corresponds to a
discriminant of the operand type, its value is that of the
corresponding discriminant of the operand value; if it
corresponds to more than one discriminant of the operand type,
a check is made that all these discriminants are equal in the
operand value.
4. For each discriminant of the target type that corresponds to a
discriminant that is specified by the derived_type_definition
for some ancestor of the operand type (or if class-wide, some
ancestor of the specific type identified by the tag of the
operand), its value in the result is that specified by the
derived_type_definition.
5. For each discriminant of the operand type that corresponds to a
discriminant that is specified by the derived_type_definition
for some ancestor of the target type, a check is made that in
the operand value it equals the value specified for it.
6. For each discriminant of the result, a check is made that its
value belongs to its subtype.
a. Access Type Conversion
1. For an access-to-object type, a check is made that the
accessibility level of the operand type is not deeper than that
of the target type.
2. If the target type is an anonymous access type, a check is made
that the value of the operand is not null; if the target is not
an anonymous access type, then the result is null if the
operand value is null.
3. If the operand value is not null, then the result designates
the same object (or subprogram) as is designated by the operand
value, but viewed as being of the target designated subtype (or
profile); any checks associated with evaluating a conversion to
the target designated subtype are performed.
1. After conversion of the value to the target type, if the target subtype
is constrained, a check is performed that the value satisfies this
constraint.
2. For the evaluation of a view conversion, the operand name is evaluated,
and a new view of the object denoted by the operand is created, whose
type is the target type; if the target type is composite, checks are
performed as above for a value conversion.
3. The properties of this new view are as follows:
a. If the target type is composite, the bounds or discriminants (if
any) of the view are as defined above for a value conversion; each
nondiscriminant component of the view denotes the matching component
of the operand object; the subtype of the view is constrained if
either the target subtype or the operand object is constrained, or
if the operand type is a descendant of the target type, and has
discriminants that were not inherited from the target type;
b. If the target type is tagged, then an assignment to the view assigns
to the corresponding part of the object denoted by the operand;
otherwise, an assignment to the view assigns to the object, after
converting the assigned value to the subtype of the object (which
might raise Constraint_Error);
c. Reading the value of the view yields the result of converting the
value of the operand object to the target subtype (which might raise
Constraint_Error), except if the object is of an access type and the
view conversion is passed as an out parameter; in this latter case,
the value of the operand object is used to initialize the formal
parameter without checking against any constraint of the target
subtype (see 6.4.1).
1. If an Accessibility_Check fails, Program_Error is raised. Any other check
associated with a conversion raises Constraint_Error if it fails.
2. Conversion to a type is the same as conversion to an unconstrained
subtype of the type.
NOTES
3. (20) In addition to explicit type_conversions, type conversions are
performed implicitly in situations where the expected type and the actual
type of a construct differ, as is permitted by the type resolution rules,
see 8.6. For example, an integer literal is of the type
universal_integer, and is implicitly converted when assigned to a target
of some specific integer type. Similarly, an actual parameter of a
specific tagged type is implicitly converted when the corresponding
formal parameter is of a class-wide type.
4. Even when the expected and actual types are the same, implicit subtype
conversions are performed to adjust the array bounds (if any) of an
operand to match the desired target subtype, or to raise Constraint_Error
if the (possibly adjusted) value does not satisfy the constraints of the
target subtype.
5. (21) A ramification of the overload resolution rules is that the operand
of an (explicit) type_conversion cannot be the literal null, an
allocator, an aggregate, a string_literal, a character_literal, or an
attribute_reference for an Access or Unchecked_Access attribute.
Similarly, such an expression enclosed by parentheses is not allowed. A
qualified_expression, see 4.7, can be used instead of such a
type_conversion.
6. (22) The constraint of the target subtype has no effect for a
type_conversion of an elementary type passed as an out parameter. Hence,
it is recommended that the first subtype be specified as the target to
minimize confusion (a similar recommendation applies to renaming and
generic formal in out objects).
Examples
7. Examples of numeric type conversion:
8.
Real(2*J) -- value is converted to floating point
Integer(1.6) -- value is 2
Integer(-0.4) -- value is 0
9. Example of conversion between derived types:
10.
type A_Form is new B_Form;
11.
X : A_Form;
Y : B_Form;
12.
X := A_Form(Y);
Y := B_Form(X); -- the reverse conversion
13. Examples of conversions between array types:
14.
type Sequence is array (Integer range <>) of Integer;
subtype Dozen is Sequence(1 ┬╖┬╖ 12);
Ledger : array(1 ┬╖┬╖ 100) of Integer;
15.
Sequence(Ledger) -- bounds are those of Ledger
Sequence(Ledger(31 ┬╖┬╖ 42)) -- bounds are 31 and 42
Dozen(Ledger(31 ┬╖┬╖ 42)) -- bounds are those of Dozen
ΓòÉΓòÉΓòÉ 7.7. Qualified Expressions ΓòÉΓòÉΓòÉ
1. A qualified_expression is used to state explicitly the type, and to
verify the subtype, of an operand that is either an expression or an
aggregate.
Syntax
2.
qualified_expression ::=
subtype_mark'(expression) | subtype_mark'aggregate
Name Resolution Rules
3. The operand (the expression or aggregate) shall resolve to be of the type
determined by the subtype_mark, or a universal type that covers it.
Dynamic Semantics
4. The evaluation of a qualified_expression evaluates the operand (and if of
a universal type, converts it to the type determined by the subtype_mark)
and checks that its value belongs to the subtype denoted by the
subtype_mark. The exception Constraint_Error is raised if this check
fails.
NOTES
5. (23) When a given context does not uniquely identify an expected type, a
qualified_expression can be used to do so. In particular, if an
overloaded name or aggregate is passed to an overloaded subprogram, it
might be necessary to qualify the operand to resolve its type.
Examples
6. Examples of disambiguating expressions using qualification:
7.
type Mask is (Fix, Dec, Exp, Signif);
type Code is (Fix, Cla, Dec, Tnz, Sub);
8.
Print (Mask'(Dec)); -- Dec is of type Mask
Print (Code'(Dec)); -- Dec is of type Code
9.
for J in Code'(Fix) ┬╖┬╖ Code'(Dec) loop ┬╖┬╖┬╖
-- qualification needed for either Fix or Dec
for J in Code range Fix ┬╖┬╖ Dec loop ┬╖┬╖┬╖
-- qualification unnecessary
for J in Code'(Fix) ┬╖┬╖ Dec loop ┬╖┬╖┬╖
-- qualification unnecessary for Dec
10.
Dozen'(1 | 3 | 5 | 7 => 2, others => 0) -- see 4.6
ΓòÉΓòÉΓòÉ 7.8. Allocators ΓòÉΓòÉΓòÉ
1. The evaluation of an allocator creates an object and yields an access
value that designates the object.
Syntax
2.
allocator ::=
new subtype_indication | new qualified_expression
Name Resolution Rules
3. The expected type for an allocator shall be a single access-to-object
type whose designated type covers the type determined by the subtype_mark
of the subtype_indication or qualified_expression.
Legality Rules
4. An initialized allocator is an allocator with a qualified_expression. An
uninitialized allocator is one with a subtype_indication. In the
subtype_indication of an uninitialized allocator, a constraint is
permitted only if the subtype_mark denotes an unconstrained composite
subtype; if there is no constraint, then the subtype_mark shall denote a
definite subtype.
5. If the type of the allocator is an access-to-constant type, the allocator
shall be an initialized allocator. If the designated type is limited, the
allocator shall be an uninitialized allocator.
Static Semantics
6. If the designated type of the type of the allocator is elementary, then
the subtype of the created object is the designated subtype. If the
designated type is composite, then the created object is always
constrained; if the designated subtype is constrained, then it provides
the constraint of the created object; otherwise, the object is
constrained by its initial value (even if the designated subtype is
unconstrained with defaults).
Dynamic Semantics
7. For the evaluation of an allocator, the elaboration of the
subtype_indication or the evaluation of the qualified_expression is
performed first. For the evaluation of an initialized allocator, an
object of the designated type is created and the value of the
qualified_expression is converted to the designated subtype and assigned
to the object.
8. For the evaluation of an uninitialized allocator:
a. If the designated type is elementary, an object of the designated
subtype is created and any implicit initial value is assigned;
b. If the designated type is composite, an object of the designated
type is created with tag, if any, determined by the subtype_mark of
the subtype_indication; any per-object constraints on subcomponents
are elaborated and any implicit initial values for the subcomponents
of the object are obtained as determined by the subtype_indication
and assigned to the corresponding subcomponents. A check is made
that the value of the object belongs to the designated subtype.
Constraint_Error is raised if this check fails. This check and the
initialization of the object are performed in an arbitrary order.
1. If the created object contains any tasks, they are activated (see 9.2).
Finally, an access value that designates the created object is returned.
NOTES
2. (24) Allocators cannot create objects of an abstract type (see 3.9.3).
3. (25) If any part of the created object is controlled, the initialization
includes calls on corresponding Initialize or Adjust procedures (see
7.6).
4. (26) As explained in 13.11: ``Storage Management'', the storage for an
object allocated by an allocator comes from a storage pool (possibly user
defined). The exception Storage_Error is raised by an allocator if there
is not enough storage. Instances of Unchecked_Deallocation may be used to
explicitly reclaim storage.
5. (27) Implementations are permitted, but not required, to provide garbage
collection, see 13.11.3.
Examples
6. Examples of allocators:
7.
new Cell'(0, null, null)
-- initialized explicitly, see 3.10.1
new Cell'(Value => 0, Succ => null, Pred => null)
-- initialized explicitly
new Cell
-- not initialized
8.
new Matrix(1 ┬╖┬╖ 10, 1 ┬╖┬╖ 20)
-- the bounds only are given
new Matrix'(1 ┬╖┬╖ 10 => (1 ┬╖┬╖ 20 => 0.0))
-- initialized explicitly
9.
new Buffer(100)
-- the discriminant only is given
new Buffer'(Size => 80, Pos => 0, Value => (1 ┬╖┬╖ 80 => 'A'))
-- initialized explicitly
10.
Expr_Ptr'(new Literal)
-- allocator for access-to-class-wide type, see 3.9.1
Expr_Ptr'(new Literal'(Expression with 3.5))
-- initialized explicitly
ΓòÉΓòÉΓòÉ 7.9. Static Expressions and Static Subtypes ΓòÉΓòÉΓòÉ
1. Certain expressions of a scalar or string type are defined to be static.
Similarly, certain discrete ranges are defined to be static, and certain
scalar and string subtypes are defined to be static subtypes. Static
means determinable at compile time, using the declared properties or
values of the program entities.
2. A static expression is a scalar or string expression that is one of the
following:
a. a numeric_literal;
b. a string_literal of a static string subtype;
c. a name that denotes the declaration of a named number or a static
constant;
d. a function_call whose function_name or function_prefix statically
denotes a static function, and whose actual parameters, if any
(whether given explicitly or by default), are all static
expressions;
e. an attribute_reference that denotes a scalar value, and whose prefix
denotes a static scalar subtype;
f. an attribute_reference whose prefix statically denotes a statically
constrained array object or array subtype, and whose
attribute_designator is First, Last, or Length, with an optional
dimension;
g. a type_conversion whose subtype_mark denotes a static scalar
subtype, and whose operand is a static expression;
h. a qualified_expression whose subtype_mark denotes a static (scalar
or string) subtype, and whose operand is a static expression;
i. a membership test whose simple_expression is a static expression,
and whose range is a static range or whose subtype_mark denotes a
static (scalar or string) subtype;
j. a short-circuit control form both of whose relations are static
expressions;
k. a static expression enclosed in parentheses.
1. A name statically denotes an entity if it denotes the entity and:
a. It is a direct_name, expanded name, or character_literal, and it
denotes a declaration other than a renaming_declaration; or
b. It is an attribute_reference whose prefix statically denotes some
entity; or
c. It denotes a renaming_declaration with a name that statically
denotes the renamed entity.
1. A static function is one of the following:
a. a predefined operator whose parameter and result types are all
scalar types none of which are descendants of formal scalar types;
b. a predefined concatenation operator whose result type is a string
type;
c. an enumeration literal;
d. a language-defined attribute that is a function, if the prefix
denotes a static scalar subtype, and if the parameter and result
types are scalar.
1. In any case, a generic formal subprogram is not a static function.
2. A static constant is a constant view declared by a full constant
declaration or an object_renaming_declaration with a static nominal
subtype, having a value defined by a static scalar expression or by a
static string expression whose value has a length not exceeding the
maximum length of a string_literal in the implementation.
3. A static range is a range whose bounds are static expressions, or a
range_attribute_reference that is equivalent to such a range. A static
discrete_range is one that is a static range or is a subtype_indication
that defines a static scalar subtype. The base range of a scalar type is
a static range, unless the type is a descendant of a formal scalar type.
4. A static subtype is either a static scalar subtype or a static string
subtype. A static scalar subtype is an unconstrained scalar subtype whose
type is not a descendant of a formal scalar type, or a constrained scalar
subtype formed by imposing a compatible static constraint on a static
scalar subtype. A static string subtype is an unconstrained string
subtype whose index subtype and component subtype are static (and whose
type is not a descendant of a formal array type), or a constrained string
subtype formed by imposing a compatible static constraint on a static
string subtype. In any case, the subtype of a generic formal object of
mode in out, and the result subtype of a generic formal function, are not
static.
5. The different kinds of static constraint are defined as follows:
a. A null constraint is always static;
b. A scalar constraint is static if it has no range_constraint, or one
with a static range;
c. An index constraint is static if each discrete_range is static, and
each index subtype of the corresponding array type is static;
d. A discriminant constraint is static if each expression of the
constraint is static, and the subtype of each discriminant is
static.
1. A subtype is statically constrained if it is constrained, and its
constraint is static. An object is statically constrained if its nominal
subtype is statically constrained, or if it is a static string constant.
Legality Rules
2. A static expression is evaluated at compile time except when it is part
of the right operand of a static short-circuit control form whose value
is determined by its left operand. This evaluation is performed exactly,
without performing Overflow_Checks. For a static expression that is
evaluated:
a. The expression is illegal if its evaluation fails a language-defined
check other than Overflow_Check.
b. If the expression is not part of a larger static expression, then
its value shall be within the base range of its expected type.
Otherwise, the value may be arbitrarily large or small.
c. If the expression is of type universal_real and its expected type is
a decimal fixed point type, then its value shall be a multiple of
the small of the decimal type.
1. The last two restrictions above do not apply if the expected type is a
descendant of a formal scalar type (or a corresponding actual type in an
instance).
Implementation Requirements
2. For a real static expression that is not part of a larger static
expression, and whose expected type is not a descendant of a formal
scalar type, the implementation shall round or truncate the value
(according to the Machine_Rounds attribute of the expected type) to the
nearest machine number of the expected type; if the value is exactly
half-way between two machine numbers, any rounding shall be performed
away from zero. If the expected type is a descendant of a formal scalar
type, no special rounding or truncating is required -- normal accuracy
rules apply, see G.
NOTES
3. (28) An expression can be static even if it occurs in a context where
staticness is not required.
4. (29) A static (or run-time) type_conversion from a real type to an
integer type performs rounding. If the operand value is exactly half-way
between two integers, the rounding is performed away from zero.
Examples
5. Examples of static expressions:
6.
1 + 1 -- 2
abs(-10)*3 -- 30
7.
Kilo : constant := 1000;
Mega : constant := Kilo*Kilo; -- 1_000_000
Long : constant := Float'Digits*2;
8.
Half_Pi : constant := Pi/2;
-- see 3.3.2.
Deg_To_Rad : constant := Half_Pi/90;
Rad_To_Deg : constant := 1.0/Deg_To_Rad;
-- equivalent to 1.0/((3.14159_26536/2)/90)
4.9.1 Statically Matching Constraints and Subtypes
ΓòÉΓòÉΓòÉ 7.9.1. Statically Matching Constraints and Subtypes ΓòÉΓòÉΓòÉ
Static Semantics
1. A constraint statically matches another constraint if both are null
constraints, both are static and have equal corresponding bounds or
discriminant values, or both are nonstatic and result from the same
elaboration of a constraint of a subtype_indication or the same
evaluation of a range of a discrete_subtype_definition.
2. A subtype statically matches another subtype of the same type if they
have statically matching constraints. Two anonymous access subtypes
statically match if their designated subtypes statically match.
3. Two ranges of the same type statically match if both result from the same
evaluation of a range, or if both are static and have equal corresponding
bounds.
4. A constraint is statically compatible with a scalar subtype if it
statically matches the constraint of the subtype, or if both are static
and the constraint is compatible with the subtype. A constraint is
statically compatible with an access or composite subtype if it
statically matches the constraint of the subtype, or if the subtype is
unconstrained. One subtype is statically compatible with a second subtype
if the constraint of the first is statically compatible with the second
subtype.
ΓòÉΓòÉΓòÉ 8. Statements ΓòÉΓòÉΓòÉ
1. A statement defines an action to be performed upon its execution.
2. This section describes the general rules applicable to all statements.
Some statements are discussed in later sections:
Procedure_call_statements and return_statements are described in 6:
``Subprograms''. Entry_call_statements, requeue_statements,
delay_statements, accept_statements, select_statements, and
abort_statements are described in 9: ``Tasks and Synchronization''.
Raise_statements are described in 11: ``Exceptions'', and code_statements
in 13. The remaining forms of statements are presented in this section.
5.1 Simple and Compound Statements - Sequences of
Statements
5.2 Assignment Statements
5.3 If Statements
5.4 Case Statements
5.5 Loop Statements
5.6 Block Statements
5.7 Exit Statements
5.8 Goto Statements
ΓòÉΓòÉΓòÉ 8.1. Simple and Compound Statements - Sequences of Statements ΓòÉΓòÉΓòÉ
1. A statement is either simple or compound. A simple_statement encloses no
other statement. A compound_statement can enclose simple_statements and
other compound_statements.
Syntax
2.
sequence_of_statements ::= statement {statement}
3.
statement ::=
{label} simple_statement | {label} compound_statement
4.
simple_statement ::= null_statement
| assignment_statement | exit_statement
| goto_statement | procedure_call_statement
| return_statement | entry_call_statement
| requeue_statement | delay_statement
| abort_statement | raise_statement
| code_statement
5.
compound_statement ::=
if_statement | case_statement
| loop_statement | block_statement
| accept_statement | select_statement
6.
null_statement ::= null;
7.
label ::= <<label_statement_identifier>>
8.
statement_identifier ::= direct_name
a. The direct_name of a statement_identifier shall be an identifier
(not an operator_symbol).
Name Resolution Rules
1. The direct_name of a statement_identifier shall resolve to denote its
corresponding implicit declaration (see below).
Legality Rules
2. Distinct identifiers shall be used for all statement_identifiers that
appear in the same body, including inner block_statements but excluding
inner program units.
Static Semantics
3. For each statement_identifier, there is an implicit declaration (with the
specified identifier) at the end of the declarative_part of the innermost
block_statement or body that encloses the statement_identifier. The
implicit declarations occur in the same order as the
statement_identifiers occur in the source text. If a usage name denotes
such an implicit declaration, the entity it denotes is the label,
loop_statement, or block_statement with the given statement_identifier.
Dynamic Semantics
4. The execution of a null_statement has no effect.
5. A transfer of control is the run-time action of an exit_statement,
return_statement, goto_statement, or requeue_statement, selection of a
terminate_alternative, raising of an exception, or an abort, which causes
the next action performed to be one other than what would normally be
expected from the other rules of the language. As explained in 7.6.1, a
transfer of control can cause the execution of constructs to be completed
and then left, which may trigger finalization.
6. The execution of a sequence_of_statements consists of the execution of
the individual statements in succession until the sequence_ is completed.
NOTES
7. (1) A statement_identifier that appears immediately within the
declarative region of a named loop_statement or an accept_statement is
nevertheless implicitly declared immediately within the declarative
region of the innermost enclosing body or block_statement; in other
words, the expanded name for a named statement is not affected by whether
the statement occurs inside or outside a named loop or an
accept_statement -- only nesting within block_statements is relevant to
the form of its expanded name.
Examples
8. Examples of labeled statements:
9.
<<Here>> <<Ici>> <<Aqui>> <<Hier>> null;
10.
<<After>> X := 1;
ΓòÉΓòÉΓòÉ 8.2. Assignment Statements ΓòÉΓòÉΓòÉ
1. An assignment_statement replaces the current value of a variable with the
result of evaluating an expression.
Syntax
2.
assignment_statement ::= variable_name := expression;
3. The execution of an assignment_statement includes the evaluation of the
expression and the assignment of the value of the expression into the
target. An assignment operation (as opposed to an assignment_statement)
is performed in other contexts as well, including object initialization
and by-copy parameter passing. The target of an assignment operation is
the view of the object to which a value is being assigned; the target of
an assignment_statement is the variable denoted by the variable_name.
Name Resolution Rules
4. The variable_name of an assignment_statement is expected to be of any
nonlimited type. The expected type for the expression is the type of the
target.
Legality Rules
5. The target denoted by the variable_name shall be a variable.
6. If the target is of a tagged class-wide type T'Class, then the expression
shall either be dynamically tagged, or of type T and tag-indeterminate,
see 3.9.2.
Dynamic Semantics
7. For the execution of an assignment_statement, the variable_name and the
expression are first evaluated in an arbitrary order.
8. When the type of the target is class-wide:
a. If the expression is tag-indeterminate, see 3.9.2, then the
controlling tag value for the expression is the tag of the target;
b. Otherwise (the expression is dynamically tagged), a check is made
that the tag of the value of the expression is the same as that of
the target; if this check fails, Constraint_Error is raised.
1. The value of the expression is converted to the subtype of the target.
The conversion might raise an exception, see 4.6.
2. In cases involving controlled types, the target is finalized, and an
anonymous object might be used as an intermediate in the assignment, as
described in 7.6.1: ``Completion and Finalization''. In any case, the
converted value of the expression is then assigned to the target, which
consists of the following two steps:
a. The value of the target becomes the converted value.
b. If any part of the target is controlled, its value is adjusted as
explained in 7.6.
NOTES
1. (2) The tag of an object never changes; in particular, an
assignment_statement does not change the tag of the target.
2. (3) The values of the discriminants of an object designated by an access
value cannot be changed (not even by assigning a complete value to the
object itself) since such objects are always constrained; however,
subcomponents of such objects may be unconstrained.
Examples
3. Examples of assignment statements:
4.
Value := Max_Value - 1;
Shade := Blue;
5.
Next_Frame(F)(M, N) := 2.5; -- see 4.1.1
U := Dot_Product(V, W); -- see 6.3
6.
Writer := (Status => Open, Unit => Printer, Line_Count => 60);
-- see 3.8.1
Next_Car.all := (72074, null);
-- see 3.10.1
7. Examples involving scalar subtype conversions:
8.
I, J : Integer range 1 ┬╖┬╖ 10 := 5;
K : Integer range 1 ┬╖┬╖ 20 := 15;
┬╖┬╖┬╖
9.
I := J; -- identical ranges
K := J; -- compatible ranges
J := K; -- will raise Constraint_Error if K > 10
10. Examples involving array subtype conversions:
11.
A : String(1 ┬╖┬╖ 31);
B : String(3 ┬╖┬╖ 33);
┬╖┬╖┬╖
12.
A := B; -- same number of components
13.
A(1 ┬╖┬╖ 9) := "tar sauce";
A(4 ┬╖┬╖ 12) := A(1 ┬╖┬╖ 9); -- A(1 ┬╖┬╖ 12) = "tartar sauce"
NOTES
14. (4) Notes on the examples: Assignment_statements are allowed even in the
case of overlapping slices of the same array, because the variable_name
and expression are both evaluated before copying the value into the
variable. In the above example, an implementation yielding A(1 ┬╖┬╖ 12) =
"tartartartar" would be incorrect.
ΓòÉΓòÉΓòÉ 8.3. If Statements ΓòÉΓòÉΓòÉ
1. An if_statement selects for execution at most one of the enclosed
sequences_of_statements, depending on the (truth) value of one or more
corresponding conditions.
Syntax
2.
if_statement ::=
if condition then
sequence_of_statements
{elsif condition then
sequence_of_statements}
[else
sequence_of_statements]
end if;
3.
condition ::= boolean_expression
Name Resolution Rules
4. A condition is expected to be of any boolean type.
Dynamic Semantics
5. For the execution of an if_statement, the condition specified after if,
and any conditions specified after elsif, are evaluated in succession
(treating a final else as elsif True then), until one evaluates to True
or all conditions are evaluated and yield False. If a condition evaluates
to True, then the corresponding sequence_of_statements is executed;
otherwise none of them is executed.
Examples
6. Examples of if statements:
7.
if Month = December and Day = 31 then
Month := January;
Day := 1;
Year := Year + 1;
end if;
8.
if Line_Too_Short then
raise Layout_Error;
elsif Line_Full then
New_Line;
Put(Item);
else
Put(Item);
end if;
9.
if My_Car.Owner.Vehicle /= My_Car then -- see 3.10.1
Report ("Incorrect data");
end if;
ΓòÉΓòÉΓòÉ 8.4. Case Statements ΓòÉΓòÉΓòÉ
1. A case_statement selects for execution one of a number of alternative
sequences_of_statements; the chosen alternative is defined by the value
of an expression.
Syntax
2.
case_statement ::=
case expression is
case_statement_alternative
{case_statement_alternative}
end case;
3.
case_statement_alternative ::=
when discrete_choice_list =>
sequence_of_statements
Name Resolution Rules
4. The expression is expected to be of any discrete type. The expected type
for each discrete_choice is the type of the expression.
Legality Rules
5. The expressions and discrete_ranges given as discrete_choices of a
case_statement shall be static. A discrete_choice others, if present,
shall appear alone and in the last discrete_choice_list.
6. The possible values of the expression shall be covered as follows:
a. If the expression is a name (including a type_conversion or a
function_call) having a static and constrained nominal subtype, or
is a qualified_expression whose subtype_mark denotes a static and
constrained scalar subtype, then each non-others discrete_choice
shall cover only values in that subtype, and each value of that
subtype shall be covered by some discrete_choice (either explicitly
or by others).
b. If the type of the expression is root_integer, universal_integer, or
a descendant of a formal scalar type, then the case_statement shall
have an others discrete_choice.
c. Otherwise, each value of the base range of the type of the
expression shall be covered (either explicitly or by others).
1. Two distinct discrete_choices of a case_statement shall not cover the
same value.
Dynamic Semantics
2. For the execution of a case_statement the expression is first evaluated.
3. If the value of the expression is covered by the discrete_choice_list of
some case_statement_alternative, then the sequence_of_statements of the
_alternative is executed.
4. Otherwise (the value is not covered by any discrete_choice_list, perhaps
due to being outside the base range), Constraint_Error is raised.
NOTES
5. (5) The execution of a case_statement chooses one and only one
alternative. Qualification of the expression of a case_statement by a
static subtype can often be used to limit the number of choices that need
be given explicitly.
Examples
6. Examples of case statements:
7.
case Sensor is
when Elevation => Record_Elevation(Sensor_Value);
when Azimuth => Record_Azimuth (Sensor_Value);
when Distance => Record_Distance (Sensor_Value);
when others => null;
end case;
8.
case Today is
when Mon => Compute_Initial_Balance;
when Fri => Compute_Closing_Balance;
when Tue ┬╖┬╖ Thu => Generate_Report(Today);
when Sat ┬╖┬╖ Sun => null;
end case;
9.
case Bin_Number(Count) is
when 1 => Update_Bin(1);
when 2 => Update_Bin(2);
when 3 | 4 =>
Empty_Bin(1);
Empty_Bin(2);
when others => raise Error;
end case;
ΓòÉΓòÉΓòÉ 8.5. Loop Statements ΓòÉΓòÉΓòÉ
1. A loop_statement includes a sequence_of_statements that is to be executed
repeatedly, zero or more times.
Syntax
2.
loop_statement ::=
[loop_statement_identifier:]
[iteration_scheme] loop
sequence_of_statements
end loop [loop_identifier];
3.
iteration_scheme ::= while condition
| for loop_parameter_specification
4.
loop_parameter_specification ::=
defining_identifier in [reverse] discrete_subtype_definition
a. If a loop_statement has a loop_statement_identifier, then the
identifier shall be repeated after the end loop; otherwise, there
shall not be an identifier after the end loop.
Static Semantics
1. A loop_parameter_specification declares a loop parameter, which is an
object whose subtype is that defined by the discrete_subtype_definition.
Dynamic Semantics
2. For the execution of a loop_statement, the sequence_of_statements is
executed repeatedly, zero or more times, until the loop_statement is
complete. The loop_statement is complete when a transfer of control
occurs that transfers control out of the loop, or, in the case of an
iteration_scheme, as specified below.
3. For the execution of a loop_statement with a while iteration_scheme, the
condition is evaluated before each execution of the
sequence_of_statements; if the value of the condition is True, the
sequence_of_statements is executed; if False, the execution of the
loop_statement is complete.
4. For the execution of a loop_statement with a for iteration_scheme, the
loop_parameter_specification is first elaborated. This elaboration
creates the loop parameter and elaborates the
discrete_subtype_definition. If the discrete_subtype_definition defines a
subtype with a null range, the execution of the loop_statement is
complete. Otherwise, the sequence_of_statements is executed once for each
value of the discrete subtype defined by the discrete_subtype_definition
(or until the loop is left as a consequence of a transfer of control).
Prior to each such iteration, the corresponding value of the discrete
subtype is assigned to the loop parameter. These values are assigned in
increasing order unless the reserved word reverse is present, in which
case the values are assigned in decreasing order.
NOTES
5. (6) A loop parameter is a constant; it cannot be updated within the
sequence_of_statements of the loop, see 3.3.
6. (7) An object_declaration should not be given for a loop parameter, since
the loop parameter is automatically declared by the
loop_parameter_specification. The scope of a loop parameter extends from
the loop_parameter_specification to the end of the loop_statement, and
the visibility rules are such that a loop parameter is only visible
within the sequence_of_statements of the loop.
7. (8) The discrete_subtype_definition of a for loop is elaborated just
once. Use of the reserved word reverse does not alter the discrete
subtype defined, so that the following iteration_schemes are not
equivalent; the first has a null range.
8.
for J in reverse 1 ┬╖┬╖ 0
for J in 0 ┬╖┬╖ 1
Examples
9. Example of a loop statement without an iteration scheme:
10.
loop
Get(Current_Character);
exit when Current_Character = '*';
end loop;
11. Example of a loop statement with a while iteration scheme:
12.
while Bid(N).Price < Cut_Off.Price loop
Record_Bid(Bid(N).Price);
N := N + 1;
end loop;
13. Example of a loop statement with a for iteration scheme:
14.
for J in Buffer'Range loop -- works even with a null range
if Buffer(J) /= Space then
Put(Buffer(J));
end if;
end loop;
15. Example of a loop statement with a name:
16.
Summation:
while Next /= Head loop -- see 3.10.1
Sum := Sum + Next.Value;
Next := Next.Succ;
end loop Summation;
ΓòÉΓòÉΓòÉ 8.6. Block Statements ΓòÉΓòÉΓòÉ
1. A block_statement encloses a handled_sequence_of_statements optionally
preceded by a declarative_part.
Syntax
2.
block_statement ::=
[block_statement_identifier:]
[declare
declarative_part]
begin
handled_sequence_of_statements
end [block_identifier];
a. If a block_statement has a block_statement_identifier, then the
identifier shall be repeated after the end; otherwise, there shall
not be an identifier after the end.
Static Semantics
1. A block_statement that has no explicit declarative_part has an implicit
empty declarative_part.
Dynamic Semantics
2. The execution of a block_statement consists of the elaboration of its
declarative_part followed by the execution of its
handled_sequence_of_statements.
Examples
3. Example of a block statement with a local variable:
4.
Swap:
declare
Temp : Integer;
begin
Temp := V; V := U; U := Temp;
end Swap;
ΓòÉΓòÉΓòÉ 8.7. Exit Statements ΓòÉΓòÉΓòÉ
1. An exit_statement is used to complete the execution of an enclosing
loop_statement; the completion is conditional if the exit_statement
includes a condition.
Syntax
2.
exit_statement ::= exit [loop_name] [when condition];
Name Resolution Rules
3. The loop_name, if any, in an exit_statement shall resolve to denote a
loop_statement.
Legality Rules
4. Each exit_statement applies to a loop_statement; this is the
loop_statement being exited. An exit_statement with a name is only
allowed within the loop_statement denoted by the name, and applies to
that loop_statement. An exit_statement without a name is only allowed
within a loop_statement, and applies to the innermost enclosing one. An
exit_statement that applies to a given loop_statement shall not appear
within a body or accept_statement, if this construct is itself enclosed
by the given loop_statement.
Dynamic Semantics
5. For the execution of an exit_statement, the condition, if present, is
first evaluated. If the value of the condition is True, or if there is no
condition, a transfer of control is done to complete the loop_statement.
If the value of the condition is False, no transfer of control takes
place.
NOTES
6. (9) Several nested loops can be exited by an exit_statement that names
the outer loop.
Examples
7. Examples of loops with exit statements:
8.
for N in 1 ┬╖┬╖ Max_Num_Items loop
Get_New_Item(New_Item);
Merge_Item(New_Item, Storage_File);
exit when New_Item = Terminal_Item;
end loop;
9.
Main_Cycle:
loop
-- initial statements
exit Main_Cycle when Found;
-- final statements
end loop Main_Cycle;
ΓòÉΓòÉΓòÉ 8.8. Goto Statements ΓòÉΓòÉΓòÉ
1. A goto_statement specifies an explicit transfer of control from this
statement to a target statement with a given label.
Syntax
2.
goto_statement ::= goto label_name;
Name Resolution Rules
3. The label_name shall resolve to denote a label; the statement with that
label is the target statement.
Legality Rules
4. The innermost sequence_of_statements that encloses the target statement
shall also enclose the goto_statement. Furthermore, if a goto_statement
is enclosed by an accept_statement or a body, then the target statement
shall not be outside this enclosing construct.
Dynamic Semantics
5. The execution of a goto_statement transfers control to the target
statement, completing the execution of any compound_statement that
encloses the goto_statement but does not enclose the target.
NOTES
6. (10) The above rules allow transfer of control to a statement of an
enclosing sequence_of_statements but not the reverse. Similarly, they
prohibit transfers of control such as between alternatives of a
case_statement, if_statement, or select_statement; between
exception_handlers; or from an exception_handler of a
handled_sequence_of_statements back to its sequence_of_statements.
Examples
7. Example of a loop containing a goto statement:
8.
<<Sort>>
for I in 1 ┬╖┬╖ N-1 loop
if A(I) > A(I+1) then
Exchange(A(I), A(I+1));
goto Sort;
end if;
end loop;
ΓòÉΓòÉΓòÉ 9. Subprograms ΓòÉΓòÉΓòÉ
1. A subprogram is a program unit or intrinsic operation whose execution is
invoked by a subprogram call. There are two forms of subprogram:
procedures and functions. A procedure call is a statement; a function
call is an expression and returns a value. The definition of a subprogram
can be given in two parts: a subprogram declaration defining its
interface, and a subprogram_body defining its execution. Operators and
enumeration literals are functions.
2. A callable entity is a subprogram or entry, see 9. A callable entity is
invoked by a call; that is, a subprogram call or entry call. A callable
construct is a construct that defines the action of a call upon a
callable entity: a subprogram_body, entry_body, or accept_statement.
6.1 Subprogram Declarations
6.2 Formal Parameter Modes
6.3 Subprogram Bodies
6.4 Subprogram Calls
6.5 Return Statements
6.6 Overloading of Operators --- The Detailed Node
Listing ---
6.1 Subprogram Declarations
6.2 Formal Parameter Modes
6.3 Subprogram Bodies
6.3.1 Conformance Rules
6.3.2 Inline Expansion of Subprograms
6.4 Subprogram Calls
6.4.1 Parameter Associations
6.5 Return Statements
6.6 Overloading of Operators
ΓòÉΓòÉΓòÉ 9.1. Subprogram Declarations ΓòÉΓòÉΓòÉ
1. A subprogram_declaration declares a procedure or function.
Syntax
2.
subprogram_declaration ::= subprogram_specification;
3.
abstract_subprogram_declaration ::=
subprogram_specification is abstract;
4.
subprogram_specification ::=
procedure defining_program_unit_name parameter_profile
| function defining_designator parameter_and_result_profile
5.
designator ::= [parent_unit_name . ]identifier | operator_symbol
6.
defining_designator ::=
defining_program_unit_name | defining_operator_symbol
7.
defining_program_unit_name ::=
[parent_unit_name . ]defining_identifier
a. The optional parent_unit_name is only allowed for library units (see
10.1.1).
1.
operator_symbol ::= string_literal
a. The sequence of characters in an operator_symbol shall correspond to
an operator belonging to one of the six classes of operators defined
in clause 4.5 (spaces are not allowed and the case of letters is not
significant).
1.
defining_operator_symbol ::= operator_symbol
2.
parameter_profile ::= [formal_part]
3.
parameter_and_result_profile ::= [formal_part] return subtype_mark
4.
formal_part ::=
(parameter_specification {; parameter_specification{)
5.
parameter_specification ::=
defining_identifier_list : mode subtype_mark
[:= default_expression]
| defining_identifier_list : access_definition
[:= default_expression]
6.
mode ::= [in] | in out | out
Name Resolution Rules
7. A formal parameter is an object directly visible within a subprogram_body
that represents the actual parameter passed to the subprogram in a call;
it is declared by a parameter_specification. For a formal parameter, the
expected type for its default_expression, if any, is that of the formal
parameter.
Legality Rules
8. The parameter mode of a formal parameter conveys the direction of
information transfer with the actual parameter: in, in out, or out. Mode
in is the default, and is the mode of a parameter defined by an
access_definition. The formal parameters of a function, if any, shall
have the mode in.
9. A default_expression is only allowed in a parameter_specification for a
formal parameter of mode in.
10. A subprogram_declaration or a generic_subprogram_declaration requires a
completion: a body, a renaming_declaration, see 8.5, or a pragma Import,
see B.1. A completion is not allowed for an
abstract_subprogram_declaration.
11. A name that denotes a formal parameter is not allowed within the
formal_part in which it is declared, nor within the formal_part of a
corresponding body or accept_statement.
Static Semantics
12. The profile of (a view of) a callable entity is either a
parameter_profile or parameter_and_result_profile; it embodies
information about the interface to that entity -- for example, the
profile includes information about parameters passed to the callable
entity. All callable entities have a profile -- enumeration literals,
other subprograms, and entries. An access-to-subprogram type has a
designated profile. Associated with a profile is a calling convention. A
subprogram_declaration declares a procedure or a function, as indicated
by the initial reserved word, with name and profile as given by its
specification.
13. The nominal subtype of a formal parameter is the subtype denoted by the
subtype_mark, or defined by the access_definition, in the
parameter_specification.
14. An access parameter is a formal in parameter specified by an
access_definition. An access parameter is of an anonymous general
access-to-variable type, see 3.10. Access parameters allow dispatching
calls to be controlled by access values.
15. The subtypes of a profile are:
a. For any non-access parameters, the nominal subtype of the parameter.
b. For any access parameters, the designated subtype of the parameter
type.
c. For any result, the result subtype.
1. The types of a profile are the types of those subtypes.
2. A subprogram declared by an abstract_subprogram_declaration is abstract;
a subprogram declared by a subprogram_declaration is not (see 3.9.3:
``Abstract Types and Subprograms'').
Dynamic Semantics
3. The elaboration of a subprogram_declaration or an
abstract_subprogram_declaration has no effect.
NOTES
4. (1) A parameter_specification with several identifiers is equivalent to a
sequence of single parameter_specifications, as explained in 3.3.
5. (2) Abstract subprograms do not have bodies, and cannot be used in a
nondispatching call, see 3.9.3: ``Abstract Types and Subprograms''.
6. (3) The evaluation of default_expressions is caused by certain calls, as
described in 6.4.1. They are not evaluated during the elaboration of the
subprogram declaration.
7. (4) Subprograms can be called recursively and can be called concurrently
from multiple tasks.
Examples
8. Examples of subprogram declarations:
9.
procedure Traverse_Tree;
procedure Increment(X : in out Integer);
procedure Right_Indent(Margin : out Line_Size); -- see 3.5.4
procedure Switch(From, To : in out Link); -- see 3.10.1
10.
function Random return Probability; -- see 3.5.7
11.
function Min_Cell(X : Link) return Cell; -- see 3.10.1
function Next_Frame(K : Positive) return Frame; -- see 3.10
function Dot_Product(Left, Right : Vector) return Real;
-- see 3.6
12.
function "*"(Left, Right : Matrix) return Matrix;
-- see 3.6
13. Examples of in parameters with default expressions:
14.
procedure Print_Header
(Pages : in Natural;
Header : in Line := (1 ┬╖┬╖ Line'Last => ' '); -- see 3.6
Center : in Boolean := True);
ΓòÉΓòÉΓòÉ 9.2. Formal Parameter Modes ΓòÉΓòÉΓòÉ
1. A parameter_specification declares a formal parameter of mode in, in out,
or out.
Static Semantics
2. A parameter is passed either by copy or by reference. When a parameter is
passed by copy, the formal parameter denotes a separate object from the
actual parameter, and any information transfer between the two occurs
only before and after executing the subprogram. When a parameter is
passed by reference, the formal parameter denotes (a view of) the object
denoted by the actual parameter; reads and updates of the formal
parameter directly reference the actual parameter object.
3. A type is a by-copy type if it is an elementary type, or if it is a
descendant of a private type whose full type is a by-copy type. A
parameter of a by-copy type is passed by copy.
4. A type is a by-reference type if it is a descendant of one of the
following:
a. a tagged type;
b. a task or protected type;
c. a nonprivate type with the reserved word limited in its declaration;
d. a composite type with a subcomponent of a by-reference type;
e. a private type whose full type is a by-reference type.
1. A parameter of a by-reference type is passed by reference. Each value of
a by-reference type has an associated object. For a parenthesized
expression, qualified_expression, or type_conversion, this object is the
one associated with the operand.
2. For parameters of other types, it is unspecified whether the parameter is
passed by copy or by reference.
Bounded (Run-Time) Errors
3. If one name denotes a part of a formal parameter, and a second name
denotes a part of a distinct formal parameter or an object that is not
part of a formal parameter, then the two names are considered distinct
access paths. If an object is of a type for which the parameter passing
mechanism is not specified, then it is a bounded error to assign to the
object via one access path, and then read the value of the object via a
distinct access path, unless the first access path denotes a part of a
formal parameter that no longer exists at the point of the second access
(due to leaving the corresponding callable construct). The possible
consequences are that Program_Error is raised, or the newly assigned
value is read, or some old value of the object is read.
NOTES
4. (5) A formal parameter of mode in is a constant view, see 3.3, it cannot
be updated within the subprogram_body.
ΓòÉΓòÉΓòÉ 9.3. Subprogram Bodies ΓòÉΓòÉΓòÉ
1. A subprogram_body specifies the execution of a subprogram.
Syntax
2.
subprogram_body ::=
subprogram_specification is
declarative_part
begin
handled_sequence_of_statements
end [designator];
a. If a designator appears at the end of a subprogram_body, it shall
repeat the defining_designator of the subprogram_specification.
Legality Rules
1. In contrast to other bodies, a subprogram_body need not be the completion
of a previous declaration, in which case the body declares the
subprogram. If the body is a completion, it shall be the completion of a
subprogram_declaration or generic_subprogram_declaration. The profile of
a subprogram_body that completes a declaration shall conform fully to
that of the declaration.
Static Semantics
2. A subprogram_body is considered a declaration. It can either complete a
previous declaration, or itself be the initial declaration of the
subprogram.
Dynamic Semantics
3. The elaboration of a non-generic subprogram_body has no other effect than
to establish that the subprogram can from then on be called without
failing the Elaboration_Check.
4. The execution of a subprogram_body is invoked by a subprogram call. For
this execution the declarative_part is elaborated, and the
handled_sequence_of_statements is then executed.
Examples
5. Example of procedure body:
6.
procedure Push(E : in Element_Type; S : in out Stack) is
begin
if S.Index = S.Size then
raise Stack_Overflow;
else
S.Index := S.Index + 1;
S.Space(S.Index) := E;
end if;
end Push;
7. Example of a function body:
8.
function Dot_Product(Left, Right : Vector) return Real is
Sum : Real := 0.0;
begin
Check(Left'First = Right'First and Left'Last = Right'Last);
for J in Left'Range loop
Sum := Sum + Left(J)*Right(J);
end loop;
return Sum;
end Dot_Product;
6.3.1 Conformance Rules
6.3.2 Inline Expansion of Subprograms
ΓòÉΓòÉΓòÉ 9.3.1. Conformance Rules ΓòÉΓòÉΓòÉ
1. When subprogram profiles are given in more than one place, they are
required to conform in one of four ways: type conformance, mode
conformance, subtype conformance, or full conformance.
Static Semantics
2. As explained in B.1: ``Interfacing Pragmas'', a convention can be
specified for an entity. For a callable entity or access-to-subprogram
type, the convention is called the calling convention. The following
conventions are defined by the language:
a. The default calling convention for any subprogram not listed below
is Ada. A pragma Convention, Import, or Export may be used to
override the default calling convention, see B.1.
b. The Intrinsic calling convention represents subprograms that are
``built in'' to the compiler. The default calling convention is
Intrinsic for the following:
a. an enumeration literal;
b. a "/=" operator declared implicitly due to the declaration
of "=" (see 6.6);
c. any other implicitly declared subprogram unless it is a
dispatching operation of a tagged type;
d. an inherited subprogram of a generic formal tagged type
with unknown discriminants;
e. an attribute that is a subprogram;
f. a subprogram declared immediately within a protected_body.
1. The Access attribute is not allowed for Intrinsic subprograms.
a. The default calling convention is protected for a protected
subprogram, and for an access-to-subprogram type with the reserved
word protected in its definition.
b. The default calling convention is entry for an entry.
1. Of these four conventions, only Ada and Intrinsic are allowed as a
convention_identifier in a pragma Convention, Import, or Export.
2. Two profiles are type conformant if they have the same number of
parameters, and both have a result if either does, and corresponding
parameter and result types are the same, or, for access parameters,
corresponding designated types are the same.
3. Two profiles are mode conformant if they are type-conformant, and
corresponding parameters have identical modes, and, for access
parameters, the designated subtypes statically match.
4. Two profiles are subtype conformant if they are mode-conformant,
corresponding subtypes of the profile statically match, and the
associated calling conventions are the same. The profile of a generic
formal subprogram is not subtype-conformant with any other profile.
5. Two profiles are fully conformant if they are subtype-conformant, and
corresponding parameters have the same names and have default_expressions
that are fully conformant with one another.
6. Two expressions are fully conformant if, after replacing each use of an
operator with the equivalent function_call:
a. each constituent construct of one corresponds to an instance of the
same syntactic category in the other, except that an expanded name
may correspond to a direct_name (or character_literal) or to a
different expanded name in the other; and
b. each direct_name, character_literal, and selector_name that is not
part of the prefix of an expanded name in one denotes the same
declaration as the corresponding direct_name, character_literal, or
selector_name in the other; and
c. each primary that is a literal in one has the same value as the
corresponding literal in the other.
1. Two known_discriminant_parts are fully conformant if they have the same
number of discriminants, and discriminants in the same positions have the
same names, statically matching subtypes, and default_expressions that
are fully conformant with one another.
2. Two discrete_subtype_definitions are fully conformant if they are both
subtype_indications or are both ranges, the subtype_marks (if any) denote
the same subtype, and the corresponding simple_expressions of the ranges
(if any) fully conform.
Implementation Permissions
3. An implementation may declare an operator declared in a language-defined
library unit to be intrinsic.
ΓòÉΓòÉΓòÉ 9.3.2. Inline Expansion of Subprograms ΓòÉΓòÉΓòÉ
1. Subprograms may be expanded in line at the call site.
Syntax
2. The form of a pragma Inline, which is a program unit pragma (see 10.1.5)
is as follows:
3.
pragma Inline(name {, name{);
Legality Rules
4. The pragma shall apply to one or more callable entities or generic
subprograms.
Static Semantics
5. If a pragma Inline applies to a callable entity, this indicates that
inline expansion is desired for all calls to that entity. If a pragma
Inline applies to a generic subprogram, this indicates that inline
expansion is desired for all calls to all instances of that generic
subprogram.
Implementation Permissions
6. For each call, an implementation is free to follow or to ignore the
recommendation expressed by the pragma.
NOTES
7. (6) The name in a pragma Inline can denote more than one entity in the
case of overloading. Such a pragma applies to all of the denoted
entities.
ΓòÉΓòÉΓòÉ 9.4. Subprogram Calls ΓòÉΓòÉΓòÉ
1. A subprogram call is either a procedure_call_statement or a
function_call; it invokes the execution of the subprogram_body. The call
specifies the association of the actual parameters, if any, with formal
parameters of the subprogram.
Syntax
2.
procedure_call_statement ::=
procedure_name;
| procedure_prefix actual_parameter_part;
3.
function_call ::=
function_name
| function_prefix actual_parameter_part
4.
actual_parameter_part ::=
(parameter_association {, parameter_association{)
5.
parameter_association ::=
[formal_parameter_selector_name =>] explicit_actual_parameter
6.
explicit_actual_parameter ::= expression | variable_name
a. A parameter_association is named or positional according to whether
or not the formal_parameter_selector_name is specified. Any
positional associations shall precede any named associations. Named
associations are not allowed if the prefix in a subprogram call is
an attribute_reference.
Name Resolution Rules
1. The name or prefix given in a procedure_call_statement shall resolve to
denote a callable entity that is a procedure, or an entry renamed as
(viewed as) a procedure. The name or prefix given in a function_call
shall resolve to denote a callable entity that is a function. When there
is an actual_parameter_part, the prefix can be an implicit_dereference of
an access-to-subprogram value.
2. A subprogram call shall contain at most one association for each formal
parameter. Each formal parameter without an association shall have a
default_expression (in the profile of the view denoted by the name or
prefix). This rule is an overloading rule, see 8.6.
Dynamic Semantics
3. For the execution of a subprogram call, the name or prefix of the call is
evaluated, and each parameter_association is evaluated, see 6.4.1. If a
default_expression is used, an implicit parameter_association is assumed
for this rule. These evaluations are done in an arbitrary order. The
subprogram_body is then executed. Finally, if the subprogram completes
normally, then after it is left, any necessary assigning back of formal
to actual parameters occurs, see 6.4.1.
4. The exception Program_Error is raised at the point of a function_call if
the function completes normally without executing a return_statement.
5. A function_call denotes a constant, as defined in 6.5, the nominal
subtype of the constant is given by the result subtype of the function.
Examples
6. Examples of procedure calls:
7.
Traverse_Tree; -- see 6.1
Print_Header(128, Title, True); -- see 6.1
8.
Switch(From => X, To => Next);
-- see 6.1.
Print_Header(128, Header => Title, Center => True);
-- see 6.1.
Print_Header(Header => Title, Center => True, Pages => 128);
-- see 6.1.
9. Examples of function calls:
10.
Dot_Product(U, V) -- see 6.1, and 6.3.
Clock -- see 9.6.
F.all
-- presuming F is of an access-to-subprogram type
-- see 3.10.
11. Examples of procedures with default expressions:
12.
procedure Activate(Process : in Process_Name;
After : in Process_Name := No_Process;
Wait : in Duration := 0.0;
Prior : in Boolean := False);
13.
procedure Pair(Left, Right : in Person_Name := new Person);
-- see 3.10.1.
14. Examples of their calls:
15.
Activate(X);
Activate(X, After => Y);
Activate(X, Wait => 60.0, Prior => True);
Activate(X, Y, 10.0, False);
16.
Pair;
Pair(Left => new Person, Right => new Person);
NOTES
17. (7) If a default_expression is used for two or more parameters in a
multiple parameter_specification, the default_expression is evaluated
once for each omitted parameter. Hence in the above examples, the two
calls of Pair are equivalent.
Examples
18. Examples of overloaded subprograms:
19.
procedure Put(X : in Integer);
procedure Put(X : in String);
20.
procedure Set(Tint : in Color);
procedure Set(Signal : in Light);
21. Examples of their calls:
22.
Put(28);
Put("no possible ambiguity here");
23.
Set(Tint => Red);
Set(Signal => Red);
Set(Color'(Red));
24.
-- Set(Red) would be ambiguous since Red may
-- denote a value either of type Color or of type Light
6.4.1 Parameter Associations
ΓòÉΓòÉΓòÉ 9.4.1. Parameter Associations ΓòÉΓòÉΓòÉ
1. A parameter association defines the association between an actual
parameter and a formal parameter.
Name Resolution Rules
2. The formal_parameter_selector_name of a parameter_association shall
resolve to denote a parameter_specification of the view being called.
3. The actual parameter is either the explicit_actual_parameter given in a
parameter_association for a given formal parameter, or the corresponding
default_expression if no parameter_association is given for the formal
parameter. The expected type for an actual parameter is the type of the
corresponding formal parameter.
4. If the mode is in, the actual is interpreted as an expression; otherwise,
the actual is interpreted only as a name, if possible.
Legality Rules
5. If the mode is in out or out, the actual shall be a name that denotes a
variable.
6. The type of the actual parameter associated with an access parameter
shall be convertible, see 4.6, to its anonymous access type.
Dynamic Semantics
7. For the evaluation of a parameter_association:
a. The actual parameter is first evaluated.
b. For an access parameter, the access_definition is elaborated, which
creates the anonymous access type.
c. For a parameter (of any mode) that is passed by reference, see 6.2,
a view conversion of the actual parameter to the nominal subtype of
the formal parameter is evaluated, and the formal parameter denotes
that conversion.
d. For an in or in out parameter that is passed by copy, see 6.2, the
formal parameter object is created, and the value of the actual
parameter is converted to the nominal subtype of the formal
parameter and assigned to the formal.
e. For an out parameter that is passed by copy, the formal parameter
object is created, and:
1. For an access type, the formal parameter is initialized from
the value of the actual, without a constraint check;
2. For a composite type with discriminants or that has implicit
initial values for any subcomponents, see 3.3.1, the behavior
is as for an in out parameter passed by copy.
3. For any other type, the formal parameter is uninitialized. If
composite, a view conversion of the actual parameter to the
nominal subtype of the formal is evaluated (which might raise
Constraint_Error), and the actual subtype of the formal is that
of the view conversion. If elementary, the actual subtype of
the formal is given by its nominal subtype.
1. A formal parameter of mode in out or out with discriminants is
constrained if either its nominal subtype or the actual parameter is
constrained.
2. After normal completion and leaving of a subprogram, for each in out or
out parameter that is passed by copy, the value of the formal parameter
is converted to the subtype of the variable given as the actual parameter
and assigned to it. These conversions and assignments occur in an
arbitrary order.
ΓòÉΓòÉΓòÉ 9.5. Return Statements ΓòÉΓòÉΓòÉ
1. A return_statement is used to complete the execution of the innermost
enclosing subprogram_body, entry_body, or accept_statement.
Syntax
2.
return_statement ::= return [expression];
Name Resolution Rules
3. The expression, if any, of a return_statement is called the return
expression. The result subtype of a function is the subtype denoted by
the subtype_mark after the reserved word return in the profile of the
function. The expected type for a return expression is the result type of
the corresponding function.
Legality Rules
4. A return_statement shall be within a callable construct, and it applies
to the innermost one. A return_statement shall not be within a body that
is within the construct to which the return_statement applies.
5. A function body shall contain at least one return_statement that applies
to the function body, unless the function contains code_statements. A
return_statement shall include a return expression if and only if it
applies to a function body.
Dynamic Semantics
6. For the execution of a return_statement, the expression (if any) is first
evaluated and converted to the result subtype.
7. If the result type is class-wide, then the tag of the result is the tag
of the value of the expression.
8. If the result type is a specific tagged type:
a. If it is limited, then a check is made that the tag of the value of
the return expression identifies the result type. Constraint_Error
is raised if this check fails.
b. If it is nonlimited, then the tag of the result is that of the
result type.
1. A type is a return-by-reference type if it is a descendant of one of the
following:
a. a tagged limited type;
b. a task or protected type;
c. a nonprivate type with the reserved word limited in its declaration;
d. a composite type with a subcomponent of a return-by-reference type;
e. a private type whose full type is a return-by-reference type.
1. If the result type is a return-by-reference type, then a check is made
that the return expression is one of the following:
a. a name that denotes an object view whose accessibility level is not
deeper than that of the master that elaborated the function body; or
b. a parenthesized expression or qualified_expression whose operand is
one of these kinds of expressions.
1. The exception Program_Error is raised if this check fails.
2. For a function with a return-by-reference result type the result is
returned by reference; that is, the function call denotes a constant view
of the object associated with the value of the return expression. For any
other function, the result is returned by copy; that is, the converted
value is assigned into an anonymous constant created at the point of the
return_statement, and the function call denotes that object.
3. Finally, a transfer of control is performed which completes the execution
of the callable construct to which the return_statement applies, and
returns to the caller.
Examples
4. Examples of return statements:
5.
return;
-- in a procedure body, entry_body, or accept_statement
return Key_Value(Last_Index);
-- in a function body
ΓòÉΓòÉΓòÉ 9.6. Overloading of Operators ΓòÉΓòÉΓòÉ
1. An operator is a function whose designator is an operator_symbol.
Operators, like other functions, may be overloaded.
Name Resolution Rules
2. Each use of a unary or binary operator is equivalent to a function_call
with function_prefix being the corresponding operator_symbol, and with
(respectively) one or two positional actual parameters being the
operand(s) of the operator (in order).
Legality Rules
3. The subprogram_specification of a unary or binary operator shall have one
or two parameters, respectively. A generic function instantiation whose
designator is an operator_symbol is only allowed if the specification of
the generic function has the corresponding number of parameters.
4. Default_expressions are not allowed for the parameters of an operator
(whether the operator is declared with an explicit
subprogram_specification or by a generic_instantiation).
5. An explicit declaration of "/=" shall not have a result type of the
predefined type Boolean.
Static Semantics
6. A declaration of "=" whose result type is Boolean implicitly declares a
declaration of "/=" that gives the complementary result.
NOTES
7. (8) The operators "+" and "-" are both unary and binary operators, and
hence may be overloaded with both one- and two-parameter functions.
Examples
8. Examples of user-defined operators:
9.
function "+" (Left, Right : Matrix) return Matrix;
function "+" (Left, Right : Vector) return Vector;
-- assuming that A, B, and C are of the type Vector
-- the following two statements are equivalent:
A := B + C;
A := "+"(B, C);
ΓòÉΓòÉΓòÉ 10. Packages ΓòÉΓòÉΓòÉ
1. Packages are program units that allow the specification of groups of
logically related entities. Typically, a package contains the declaration
of a type (often a private type or private extension) along with the
declarations of primitive subprograms of the type, which can be called
from outside the package, while their inner workings remain hidden from
outside users.
7.1 Package Specifications and Declarations
7.2 Package Bodies
7.3 Private Types and Private Extensions
7.4 Deferred Constants
7.5 Limited Types
7.6 User-Defined Assignment and Finalization --- The
Detailed Node Listing ---
7.1 Package Specifications and Declarations
7.2 Package Bodies
7.3 Private Types and Private Extensions
7.3.1 Private Operations
7.4 Deferred Constants
7.5 Limited Types
7.6 User-Defined Assignment and Finalization
7.6.1 Completion and Finalization
ΓòÉΓòÉΓòÉ 10.1. Package Specifications and Declarations ΓòÉΓòÉΓòÉ
1. A package is generally provided in two parts: a package_specification and
a package_body. Every package has a package_specification, but not all
packages have a package_body.
Syntax
2.
package_declaration ::= package_specification;
3.
package_specification ::=
package defining_program_unit_name is
{basic_declarative_item}
[private
{basic_declarative_item}]
end [[parent_unit_name.]identifier]
a. If an identifier or parent_unit_name.identifier appears at the end
of a package_specification, then this sequence of lexical elements
shall repeat the defining_program_unit_name.
Legality Rules
1. A package_declaration or generic_package_declaration requires a
completion (a body) if it contains any declarative_item that requires a
completion, but whose completion is not in its package_specification.
Static Semantics
2. The first list of declarative_items of a package_specification of a
package other than a generic formal package is called the visible part of
the package. The optional list of declarative_items after the reserved
word private (of any package_specification) is called the private part of
the package. If the reserved word private does not appear, the package
has an implicit empty private part.
3. An entity declared in the private part of a package is visible only
within the declarative region of the package itself (including any child
units -- see 10.1.1. In contrast, expanded names denoting entities
declared in the visible part can be used even outside the package;
furthermore, direct visibility of such entities can be achieved by means
of use_clauses, see 4.1.3, and 8.4.
Dynamic Semantics
4. The elaboration of a package_declaration consists of the elaboration of
its basic_declarative_items in the given order.
NOTES
5. (1) The visible part of a package contains all the information that
another program unit is able to know about the package.
6. (2) If a declaration occurs immediately within the specification of a
package, and the declaration has a corresponding completion that is a
body, then that body has to occur immediately within the body of the
package.
Examples
7. Example of a package declaration:
8.
package Rational_Numbers is
9.
type Rational is
record
Numerator : Integer;
Denominator : Positive;
end record;
10.
function "="(X,Y : Rational) return Boolean;
11.
function "/" (X,Y : Integer) return Rational;
-- to construct a rational number
12.
function "+" (X,Y : Rational) return Rational;
function "-" (X,Y : Rational) return Rational;
function "*" (X,Y : Rational) return Rational;
function "/" (X,Y : Rational) return Rational;
end Rational_Numbers;
13. There are also many examples of package declarations in the predefined
language environment, see A: ``Annex A''.
ΓòÉΓòÉΓòÉ 10.2. Package Bodies ΓòÉΓòÉΓòÉ
1. In contrast to the entities declared in the visible part of a package,
the entities declared in the package_body are visible only within the
package_body itself. As a consequence, a package with a package_body can
be used for the construction of a group of related subprograms in which
the logical operations available to clients are clearly isolated from the
internal entities.
Syntax
2.
package_body ::=
package body defining_program_unit_name is
declarative_part
[begin
handled_sequence_of_statements]
end [[parent_unit_name.]identifier];
a. If an identifier or parent_unit_name.identifier appears at the end
of a package_body, then this sequence of lexical elements shall
repeat the defining_program_unit_name.
Legality Rules
1. A package_body shall be the completion of a previous package_declaration
or generic_package_declaration. A library package_declaration or library
generic_package_declaration shall not have a body unless it requires a
body; pragma Elaborate_Body can be used to require a
library_unit_declaration to have a body, see 10.2.1, if it would not
otherwise require one.
Static Semantics
2. In any package_body without statements there is an implicit
null_statement. For any package_declaration without an explicit
completion, there is an implicit package_body containing a single
null_statement. For a noninstance, nonlibrary package, this body occurs
at the end of the declarative_part of the innermost enclosing program
unit or block_statement; if there are several such packages, the order of
the implicit package_bodies is unspecified. (For an instance, the
implicit package_body occurs at the place of the instantiation (see
12.3). For a library package, the place is partially determined by the
elaboration dependences, see 10: ``Section 10''.
Dynamic Semantics
3. For the elaboration of a nongeneric package_body, its declarative_part is
first elaborated, and its handled_sequence_of_statements is then
executed.
NOTES
4. (3) A variable declared in the body of a package is only visible within
this body and, consequently, its value can only be changed within the
package_body. In the absence of local tasks, the value of such a variable
remains unchanged between calls issued from outside the package to
subprograms declared in the visible part. The properties of such a
variable are similar to those of a ``static'' variable of C.
5. (4) The elaboration of the body of a subprogram explicitly declared in
the visible part of a package is caused by the elaboration of the body of
the package. Hence a call of such a subprogram by an outside program unit
raises the exception Program_Error if the call takes place before the
elaboration of the package_body, see 3.11.
Examples
6. Example of a package body, see 7.1
7.
package body Rational_Numbers is
8.
procedure Same_Denominator (X,Y : in out Rational) is
begin
-- reduces X and Y to the same denominator:
┬╖┬╖┬╖
end Same_Denominator;
9.
function "="(X,Y : Rational) return Boolean is
U : Rational := X;
V : Rational := Y;
begin
Same_Denominator (U,V);
return U.Numerator = V.Numerator;
end "=";
10.
function "/" (X,Y : Integer) return Rational is
begin
if Y > 0 then
return (Numerator => X, Denominator => Y);
else
return (Numerator => -X, Denominator => -Y);
end if;
end "/";
11.
function "+" (X,Y : Rational) return Rational is ┬╖┬╖┬╖ end "+";
function "-" (X,Y : Rational) return Rational is ┬╖┬╖┬╖ end "-";
function "*" (X,Y : Rational) return Rational is ┬╖┬╖┬╖ end "*";
function "/" (X,Y : Rational) return Rational is ┬╖┬╖┬╖ end "/";
12.
end Rational_Numbers;
ΓòÉΓòÉΓòÉ 10.3. Private Types and Private Extensions ΓòÉΓòÉΓòÉ
1. The declaration (in the visible part of a package) of a type as a private
type or private extension serves to separate the characteristics that can
be used directly by outside program units (that is, the logical
properties) from other characteristics whose direct use is confined to
the package (the details of the definition of the type itself). See
3.9.1, for an overview of type extensions.
Syntax
2.
private_type_declaration ::=
type defining_identifier [discriminant_part] is
[[abstract] tagged] [limited] private;
3.
private_extension_declaration ::=
type defining_identifier [discriminant_part] is
[abstract] new ancestor_subtype_indication with private;
Legality Rules
4. A private_type_declaration or private_extension_declaration declares a
partial view of the type; such a declaration is allowed only as a
declarative_item of the visible part of a package, and it requires a
completion, which shall be a full_type_declaration that occurs as a
declarative_item of the private part of the package. The view of the type
declared by the full_type_declaration is called the full view. A generic
formal private type or a generic formal private extension is also a
partial view.
5. A type shall be completely defined before it is frozen, see 3.11.1, and
13.14. Thus, neither the declaration of a variable of a partial view of a
type, nor the creation by an allocator of an object of the partial view
are allowed before the full declaration of the type. Similarly, before
the full declaration, the name of the partial view cannot be used in a
generic_instantiation or in a representation item.
6. A private type is limited if its declaration includes the reserved word
limited; a private extension is limited if its ancestor type is limited.
If the partial view is nonlimited, then the full view shall be
nonlimited. If a tagged partial view is limited, then the full view shall
be limited. On the other hand, if an untagged partial view is limited,
the full view may be limited or nonlimited.
7. If the partial view is tagged, then the full view shall be tagged. On the
other hand, if the partial view is untagged, then the full view may be
tagged or untagged. In the case where the partial view is untagged and
the full view is tagged, no derivatives of the partial view are allowed
within the immediate scope of the partial view; derivatives of the full
view are allowed.
8. The ancestor subtype of a private_extension_declaration is the subtype
defined by the ancestor_subtype_indication; the ancestor type shall be a
specific tagged type. The full view of a private extension shall be
derived (directly or indirectly) from the ancestor type. In addition to
the places where Legality Rules normally apply, see 12.3, the requirement
that the ancestor be specific applies also in the private part of an
instance of a generic unit.
9. If the declaration of a partial view includes a known_discriminant_part,
then the full_type_declaration shall have a fully conforming (explicit)
known_discriminant_part, see 6.3.1: ``Conformance Rules''. The ancestor
subtype may be unconstrained; the parent subtype of the full view is
required to be constrained, see 3.7.
10. If a private extension inherits known discriminants from the ancestor
subtype, then the full view shall also inherit its discriminants from the
ancestor subtype, and the parent subtype of the full view shall be
constrained if and only if the ancestor subtype is constrained.
11. If a partial view has unknown discriminants, then the
full_type_declaration may define a definite or an indefinite subtype,
with or without discriminants.
12. If a partial view has neither known nor unknown discriminants, then the
full_type_declaration shall define a definite subtype.
13. If the ancestor subtype of a private extension has constrained
discriminants, then the parent subtype of the full view shall impose a
statically matching constraint on those discriminants.
Static Semantics
14. A private_type_declaration declares a private type and its first subtype.
Similarly, a private_extension_declaration declares a private extension
and its first subtype.
15. A declaration of a partial view and the corresponding
full_type_declaration define two views of a single type. The declaration
of a partial view together with the visible part define the operations
that are available to outside program units; the declaration of the full
view together with the private part define other operations whose direct
use is possible only within the declarative region of the package itself.
Moreover, within the scope of the declaration of the full view, the
characteristics of the type are determined by the full view; in
particular, within its scope, the full view determines the classes that
include the type, which components, entries, and protected subprograms
are visible, what attributes and other predefined operations are allowed,
and whether the first subtype is static (see 7.3.1).
16. A private extension inherits components (including discriminants unless
there is a new discriminant_part specified) and user-defined primitive
subprograms from its ancestor type, in the same way that a record
extension inherits components and user-defined primitive subprograms from
its parent type, see 3.4.
Dynamic Semantics
17. The elaboration of a private_type_declaration creates a partial view of a
type. The elaboration of a private_extension_declaration elaborates the
ancestor_subtype_indication, and creates a partial view of a type.
NOTES
18. (5) The partial view of a type as declared by a private_type_declaration
is defined to be a composite view (in 3.2). The full view of the type
might or might not be composite. A private extension is also composite,
as is its full view.
19. (6) Declaring a private type with an unknown_discriminant_part is a way
of preventing clients from creating uninitialized objects of the type;
they are then forced to initialize each object by calling some operation
declared in the visible part of the package. If such a type is also
limited, then no objects of the type can be declared outside the scope of
the full_type_declaration, restricting all object creation to the package
defining the type. This allows complete control over all storage
allocation for the type. Objects of such a type can still be passed as
parameters, however.
20. (7) The ancestor type specified in a private_extension_declaration and
the parent type specified in the corresponding declaration of a record
extension given in the private part need not be the same -- the parent
type of the full view can be any descendant of the ancestor type. In this
case, for a primitive subprogram that is inherited from the ancestor type
and not overridden, the formal parameter names and default expressions
(if any) come from the corresponding primitive subprogram of the
specified ancestor type, while the body comes from the corresponding
primitive subprogram of the parent type of the full view (see 3.9.2).
Examples
21. Examples of private type declarations:
22.
type Key is private;
type File_Name is limited private;
23. Example of a private extension declaration:
24.
type List is new Ada.Finalization.Controlled with private;
7.3.1 Private Operations
ΓòÉΓòÉΓòÉ 10.3.1. Private Operations ΓòÉΓòÉΓòÉ
1. For a type declared in the visible part of a package or generic package,
certain operations on the type do not become visible until later in the
package -- either in the private part or the body. Such private
operations are available only inside the declarative region of the
package or generic package.
Static Semantics
2. The predefined operators that exist for a given type are determined by
the classes to which the type belongs. For example, an integer type has a
predefined "+" operator. In most cases, the predefined operators of a
type are declared immediately after the definition of the type; the
exceptions are explained below. Inherited subprograms are also implicitly
declared immediately after the definition of the type, except as stated
below.
3. For a composite type, the characteristics, see 7.3 of the type are
determined in part by the characteristics of its component types. At the
place where the composite type is declared, the only characteristics of
component types used are those characteristics visible at that place. If
later within the immediate scope of the composite type additional
characteristics become visible for a component type, then any
corresponding characteristics become visible for the composite type. Any
additional predefined operators are implicitly declared at that place.
4. The corresponding rule applies to a type defined by a
derived_type_definition, if there is a place within its immediate scope
where additional characteristics of its parent type become visible.
5. For example, an array type whose component type is limited private
becomes nonlimited if the full view of the component type is nonlimited
and visible at some later place within the immediate scope of the array
type. In such a case, the predefined "=" operator is implicitly declared
at that place, and assignment is allowed after that place.
6. Inherited primitive subprograms follow a different rule. For a
derived_type_definition, each inherited primitive subprogram is
implicitly declared at the earliest place, if any, within the immediate
scope of the type_declaration, but after the type_declaration, where the
corresponding declaration from the parent is visible. If there is no such
place, then the inherited subprogram is not declared at all. An inherited
subprogram that is not declared at all cannot be named in a call and
cannot be overridden, but for a tagged type, it is possible to dispatch
to it.
7. For a private_extension_declaration, each inherited subprogram is
declared immediately after the private_extension_declaration if the
corresponding declaration from the ancestor is visible at that place.
Otherwise, the inherited subprogram is not declared for the private
extension, though it might be for the full type.
8. The Class attribute is defined for tagged subtypes in 3.9. In addition,
for every subtype S of an untagged private type whose full view is
tagged, the following attribute is defined:
9. S'Class
Denotes the class-wide subtype corresponding to the full view
of S. This attribute is allowed only from the beginning of
the private part in which the full view is declared, until
the declaration of the full view. After the full view, the
Class attribute of the full view can be used.
NOTES
10. (8) Because a partial view and a full view are two different views of one
and the same type, outside of the defining package the characteristics of
the type are those defined by the visible part. Within these outside
program units the type is just a private type or private extension, and
any language rule that applies only to another class of types does not
apply. The fact that the full declaration might implement a private type
with a type of a particular class (for example, as an array type) is
relevant only within the declarative region of the package itself
including any child units.
11. The consequences of this actual implementation are, however, valid
everywhere. For example: any default initialization of components takes
place; the attribute Size provides the size of the full view;
finalization is still done for controlled components of the full view;
task dependence rules still apply to components that are task objects.
12. (9) Partial views provide assignment (unless the view is limited),
membership tests, selected components for the selection of discriminants
and inherited components, qualification, and explicit conversion.
13. (10) For a subtype S of a partial view, S'Size is defined, see 13.3. For
an object A of a partial view, the attributes A'Size and A'Address are
defined, see 13.3. The Position, First_Bit, and Last_Bit attributes are
also defined for discriminants and inherited components.
Examples
14. Example of a type with private operations:
15.
package Key_Manager is
type Key is private;
Null_Key : constant Key;
-- a deferred constant declaration, see 7.4
procedure Get_Key(K : out Key);
function "<" (X, Y : Key) return Boolean;
private
type Key is new Natural;
Null_Key : constant Key := Key'First;
end Key_Manager;
16.
package body Key_Manager is
Last_Key : Key := Null_Key;
procedure Get_Key(K : out Key) is
begin
Last_Key := Last_Key + 1;
K := Last_Key;
end Get_Key;
17.
function "<" (X, Y : Key) return Boolean is
begin
return Natural(X) < Natural(Y);
end "<";
end Key_Manager;
NOTES
18. (11) Notes on the example: Outside of the package Key_Manager, the
operations available for objects of type Key include assignment, the
comparison for equality or inequality, the procedure Get_Key and the
operator "<"; they do not include other relational operators such as
">=", or arithmetic operators.
19. The explicitly declared operator "<" hides the predefined operator "<"
implicitly declared by the full_type_declaration. Within the body of the
function, an explicit conversion of X and Y to the subtype Natural is
necessary to invoke the "<" operator of the parent type. Alternatively,
the result of the function could be written as not (X >= Y), since the
operator ">=" is not redefined.
20. The value of the variable Last_Key, declared in the package body, remains
unchanged between calls of the procedure Get_Key (See also the NOTES of
7.2)
ΓòÉΓòÉΓòÉ 10.4. Deferred Constants ΓòÉΓòÉΓòÉ
1. Deferred constant declarations may be used to declare constants in the
visible part of a package, but with the value of the constant given in
the private part. They may also be used to declare constants imported
from other languages, see B: ``Annex B''.
Legality Rules
2. A deferred constant declaration is an object_declaration with the
reserved word constant but no initialization expression. The constant
declared by a deferred constant declaration is called a deferred
constant. A deferred constant declaration requires a completion, which
shall be a full constant declaration (called the full declaration of the
deferred constant), or a pragma Import (see B: ``Annex B'').
3. A deferred constant declaration that is completed by a full constant
declaration shall occur immediately within the visible part of a package_
specification. For this case, the following additional rules apply to the
corresponding full declaration:
a. The full declaration shall occur immediately within the private part
of the same package;
b. The deferred and full constants shall have the same type;
c. If the subtype defined by the subtype_indication in the deferred
declaration is constrained, then the subtype defined by the
subtype_indication in the full declaration shall match it
statically. On the other hand, if the subtype of the deferred
constant is unconstrained, then the full declaration is still
allowed to impose a constraint. The constant itself will be
constrained, like all constants;
d. If the deferred constant declaration includes the reserved word
aliased, then the full declaration shall also.
1. A deferred constant declaration that is completed by a pragma Import need
not appear in the visible part of a package_specification, and has no
full constant declaration.
2. The completion of a deferred constant declaration shall occur before the
constant is frozen, see 7.4.
Dynamic Semantics
3. The elaboration of a deferred constant declaration elaborates the
subtype_indication or (only allowed in the case of an imported constant)
the array_type_definition.
NOTES
4. (12) The full constant declaration for a deferred constant that is of a
given private type or private extension is not allowed before the
corresponding full_type_declaration. This is a consequence of the
freezing rules for types, see 13.14.
Examples
5. Examples of deferred constant declarations:
6.
Null_Key : constant Key; -- see 7.3.1
7.
CPU_Identifier : constant String(1┬╖┬╖8);
pragma Import(Assembler, CPU_Identifier, Link_Name => "CPU_ID");
-- see B.1
ΓòÉΓòÉΓòÉ 10.5. Limited Types ΓòÉΓòÉΓòÉ
1. A limited type is (a view of) a type for which the assignment operation
is not allowed. A nonlimited type is a (view of a) type for which the
assignment operation is allowed.
Legality Rules
2. If a tagged record type has any limited components, then the reserved
word limited shall appear in its record_type_definition.
Static Semantics
3. A type is limited if it is a descendant of one of the following:
a. a type with the reserved word limited in its definition;
b. a task or protected type;
c. a composite type with a limited component.
1. Otherwise, the type is nonlimited.
2. There are no predefined equality operators for a limited type.
NOTES
3. (13) The following are consequences of the rules for limited types:
a. An initialization expression is not allowed in an object_declaration
if the type of the object is limited.
b. A default expression is not allowed in a component_declaration if
the type of the record component is limited.
c. An initialized allocator is not allowed if the designated type is
limited.
d. A generic formal parameter of mode in must not be of a limited type.
1. (14) Aggregates are not available for a limited composite type.
Concatenation is not available for a limited array type.
2. (15) The rules do not exclude a default_expression for a formal parameter
of a limited type; they do not exclude a deferred constant of a limited
type if the full declaration of the constant is of a nonlimited type.
3. (16) As illustrated in 7.3.1, an untagged limited type can become
nonlimited under certain circumstances.
Examples
4. Example of a package with a limited type:
5.
package IO_Package is
type File_Name is limited private;
6.
procedure Open (F : in out File_Name);
procedure Close(F : in out File_Name);
procedure Read (F : in File_Name; Item : out Integer);
procedure Write(F : in File_Name; Item : in Integer);
private
type File_Name is
limited record
Internal_Name : Integer := 0;
end record;
end IO_Package;
7.
package body IO_Package is
Limit : constant := 200;
type File_Descriptor is record ┬╖┬╖┬╖ end record;
Directory : array (1 ┬╖┬╖ Limit) of File_Descriptor;
┬╖┬╖┬╖
procedure Open (F : in out File_Name) is ┬╖┬╖┬╖ end;
procedure Close(F : in out File_Name) is ┬╖┬╖┬╖ end;
procedure Read (F : in File_Name; Item : out Integer) is ┬╖┬╖┬╖ end;
procedure Write(F : in File_Name; Item : in Integer) is ┬╖┬╖┬╖ end;
begin
┬╖┬╖┬╖
end IO_Package;
NOTES
8. (17) Notes on the example: In the example above, an outside subprogram
making use of IO_Package may obtain a file name by calling Open and later
use it in calls to Read and Write. Thus, outside the package, a file name
obtained from Open acts as a kind of password; its internal properties
(such as containing a numeric value) are not known and no other
operations (such as addition or comparison of internal names) can be
performed on a file name. Most importantly, clients of the package cannot
make copies of objects of type File_Name.
9. This example is characteristic of any case where complete control over
the operations of a type is desired. Such packages serve a dual purpose.
They prevent a user from making use of the internal structure of the
type. They also implement the notion of an encapsulated data type where
the only operations on the type are those given in the package
specification.
10. The fact that the full view of File_Name is explicitly declared limited
means that parameter passing and function return will always be by
reference, see 6.2, and 6.5.
ΓòÉΓòÉΓòÉ 10.6. User-Defined Assignment and Finalization ΓòÉΓòÉΓòÉ
1. Three kinds of actions are fundamental to the manipulation of objects:
initialization, finalization, and assignment. Every object is
initialized, either explicitly or by default, after being created (for
example, by an object_declaration or allocator). Every object is
finalized before being destroyed (for example, by leaving a
subprogram_body containing an object_declaration, or by a call to an
instance of Unchecked_Deallocation). An assignment operation is used as
part of assignment_statements, explicit initialization, parameter
passing, and other operations.
2. Default definitions for these three fundamental operations are provided
by the language, but a controlled type gives the user additional control
over parts of these operations. In particular, the user can define, for a
controlled type, an Initialize procedure which is invoked immediately
after the normal default initialization of a controlled object, a
Finalize procedure which is invoked immediately before finalization of
any of the components of a controlled object, and an Adjust procedure
which is invoked as the last step of an assignment to a (nonlimited)
controlled object.
Static Semantics
3. The following language-defined library package exists:
4.
package Ada.Finalization is
pragma Preelaborate(Finalization);
5.
type Controlled is abstract tagged private;
6.
procedure Initialize(Object : in out Controlled);
procedure Adjust (Object : in out Controlled);
procedure Finalize (Object : in out Controlled);
7.
type Limited_Controlled is abstract tagged limited private;
8.
procedure Initialize(Object : in out Limited_Controlled);
procedure Finalize (Object : in out Limited_Controlled);
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Finalization;
9. A controlled type is a descendant of Controlled or Limited_Controlled.
The (default) implementations of Initialize, Adjust, and Finalize have no
effect. The predefined "=" operator of type Controlled always returns
True, since this operator is incorporated into the implementation of the
predefined equality operator of types derived from Controlled, as
explained in 4.5.2. The type Limited_Controlled is like Controlled,
except that it is limited and it lacks the primitive subprogram Adjust.
Dynamic Semantics
10. During the elaboration of an object_declaration, for every controlled
subcomponent of the object that is not assigned an initial value (as
defined in 3.3.1), Initialize is called on that subcomponent. Similarly,
if the object as a whole is controlled and is not assigned an initial
value, Initialize is called on the object. The same applies to the
evaluation of an allocator, as explained in 4.8.
11. For an extension_aggregate whose ancestor_part is a subtype_mark,
Initialize is called on all controlled subcomponents of the ancestor
part; if the type of the ancestor part is itself controlled, the
Initialize procedure of the ancestor type is called, unless that
Initialize procedure is abstract.
12. Initialize and other initialization operations are done in an arbitrary
order, except as follows. Initialize is applied to an object after
initialization of its subcomponents, if any (including both implicit
initialization and Initialize calls). If an object has a component with
an access discriminant constrained by a per-object expression, Initialize
is applied to this component after any components that do not have such
discriminants. For an object with several components with such a
discriminant, Initialize is applied to them in order of their
component_declarations. For an allocator, any task activations follow all
calls on Initialize.
13. When a target object with any controlled parts is assigned a value,
either when created or in a subsequent assignment_statement, the
assignment operation proceeds as follows:
a. The value of the target becomes the assigned value.
b. The value of the target is adjusted.
1. To adjust the value of a (nonlimited) composite object, the values of the
components of the object are first adjusted in an arbitrary order, and
then, if the object is controlled, Adjust is called. Adjusting the value
of an elementary object has no effect, nor does adjusting the value of a
composite object with no controlled parts.
2. For an assignment_statement, after the name and expression have been
evaluated, and any conversion (including constraint checking) has been
done, an anonymous object is created, and the value is assigned into it;
that is, the assignment operation is applied. (Assignment includes value
adjustment.) The target of the assignment_statement is then finalized.
The value of the anonymous object is then assigned into the target of the
assignment_statement. Finally, the anonymous object is finalized. As
explained below, the implementation may eliminate the intermediate
anonymous object, so this description subsumes the one given in 5.2:
``Assignment Statements''.
Implementation Permissions
3. An implementation is allowed to relax the above rules (for nonlimited
controlled types) in the following ways:
a. For an assignment_statement that assigns to an object the value of
that same object, the implementation need not do anything.
b. For an assignment_statement for a noncontrolled type, the
implementation may finalize and assign each component of the
variable separately (rather than finalizing the entire variable and
assigning the entire new value) unless a discriminant of the
variable is changed by the assignment.
c. For an aggregate or function call whose value is assigned into a
target object, the implementation need not create a separate
anonymous object if it can safely create the value of the aggregate
or function call directly in the target object. Similarly, for an
assignment_statement, the implementation need not create an
anonymous object if the value being assigned is the result of
evaluating a name denoting an object (the source object) whose
storage cannot overlap with the target. If the source object might
overlap with the target object, then the implementation can avoid
the need for an intermediary anonymous object by exercising one of
the above permissions and perform the assignment one component at a
time (for an overlapping array assignment), or not at all (for an
assignment where the target and the source of the assignment are the
same object). Even if an anonymous object is created, the
implementation may move its value to the target object as part of
the assignment without re-adjusting so long as the anonymous object
has no aliased subcomponents.
7.6.1 Completion and Finalization
ΓòÉΓòÉΓòÉ 10.6.1. Completion and Finalization ΓòÉΓòÉΓòÉ
1. This subclause defines completion and leaving of the execution of
constructs and entities. A master is the execution of a construct that
includes finalization of local objects after it is complete (and after
waiting for any local tasks -- see 9.3.), but before leaving. Other
constructs and entities are left immediately upon completion.
Dynamic Semantics
2. The execution of a construct or entity is complete when the end of that
execution has been reached, or when a transfer of control, see 5.1,
causes it to be abandoned. Completion due to reaching the end of
execution, or due to the transfer of control of an exit_, return_, goto_,
or requeue_statement or of the selection of a terminate_alternative is
normal completion. Completion is abnormal otherwise -- when control is
transferred out of a construct due to abort or the raising of an
exception.
3. After execution of a construct or entity is complete, it is left, meaning
that execution continues with the next action, as defined for the
execution that is taking place. Leaving an execution happens immediately
after its completion, except in the case of a master: the execution of a
task_body, a block_statement, a subprogram_body, an entry_body, or an
accept_statement. A master is finalized after it is complete, and before
it is left.
4. For the finalization of a master, dependent tasks are first awaited, as
explained in 9.3. Then each object whose accessibility level is the same
as that of the master is finalized if the object was successfully
initialized and still exists. These actions are performed whether the
master is left by reaching the last statement or via a transfer of
control. When a transfer of control causes completion of an execution,
each included master is finalized in order, from innermost outward.
5. For the finalization of an object:
a. If the object is of an elementary type, finalization has no effect;
b. If the object is of a controlled type, the Finalize procedure is
called;
c. If the object is of a protected type, the actions defined in 9.4 are
performed;
d. If the object is of a composite type, then after performing the
above actions, if any, every component of the object is finalized in
an arbitrary order, except as follows: if the object has a component
with an access discriminant constrained by a per-object expression,
this component is finalized before any components that do not have
such discriminants; for an object with several components with such
a discriminant, they are finalized in the reverse of the order of
their component_declarations.
1. Immediately before an instance of Unchecked_Deallocation reclaims the
storage of an object, the object is finalized. If an instance of
Unchecked_Deallocation is never applied to an object created by an
allocator, the object will still exist when the corresponding master
completes, and it will be finalized then.
2. The order in which the finalization of a master performs finalization of
objects is as follows: Objects created by declarations in the master are
finalized in the reverse order of their creation. For objects that were
created by allocators for an access type whose ultimate ancestor is
declared in the master, this rule is applied as though each such object
that still exists had been created in an arbitrary order at the first
freezing point, see 13.14, of the ultimate ancestor type.
3. The target of an assignment statement is finalized before copying in the
new value, as explained in 7.6.
4. The anonymous objects created by function calls and by aggregates are
finalized no later than the end of the innermost enclosing
declarative_item or statement; if that is a compound_statement, they are
finalized before starting the execution of any statement within the
compound_statement.
Bounded (Run-Time) Errors
5. It is a bounded error for a call on Finalize or Adjust to propagate an
exception. The possible consequences depend on what action invoked the
Finalize or Adjust operation:
a. For a Finalize invoked as part of an assignment_statement,
Program_Error is raised at that point.
b. For an Adjust invoked as part of an assignment operation, any other
adjustments due to be performed are performed, and then
Program_Error is raised.
c. For a Finalize invoked as part of a call on an instance of
Unchecked_Deallocation, any other finalizations due to be performed
are performed, and then Program_Error is raised.
d. For a Finalize invoked by the transfer of control of an exit_,
return_, goto_, or requeue_statement, Program_Error is raised no
earlier than after the finalization of the master being finalized
when the exception occurred, and no later than the point where
normal execution would have continued. Any other finalizations due
to be performed up to that point are performed before raising
Program_Error.
e. For a Finalize invoked by a transfer of control that is due to
raising an exception, any other finalizations due to be performed
for the same master are performed; Program_Error is raised
immediately after leaving the master.
f. For a Finalize invoked by a transfer of control due to an abort or
selection of a terminate alternative, the exception is ignored; any
other finalizations due to be performed are performed.
NOTES
1. (18) The rules in 10: ``Section 10'', imply that immediately prior to
partition termination, Finalize operations are applied to library-level
controlled objects (including those created by allocators of
library-level access types, except those already finalized). This occurs
after waiting for library-level tasks to terminate.
2. (19) A constant is only constant between its initialization and
finalization. Both initialization and finalization are allowed to change
the value of a constant.
3. (20) Abort is deferred during certain operations related to controlled
types, as explained in 9.8. Those rules prevent an abort from causing a
controlled object to be left in an ill-defined state.
4. (21) The Finalize procedure is called upon finalization of a controlled
object, even if Finalize was called earlier, either explicitly or as part
of an assignment; hence, if a controlled type is visibly controlled
(implying that its Finalize primitive is directly callable), or is
nonlimited (implying that assignment is allowed), its Finalize procedure
should be designed to have no ill effect if it is applied a second time
to the same object.
ΓòÉΓòÉΓòÉ 11. Visibility Rules ΓòÉΓòÉΓòÉ
1. The rules defining the scope of declarations and the rules defining which
identifiers, character_literals, and operator_symbols are visible at (or
from) various places in the text of the program are described in this
section. The formulation of these rules uses the notion of a declarative
region.
2. As explained in 3: Section 3, a declaration declares a view of an entity
and associates a defining name with that view. The view comprises an
identification of the viewed entity, and possibly additional properties.
A usage name denotes a declaration. It also denotes the view declared by
that declaration, and denotes the entity of that view. Thus, two
different usage names might denote two different views of the same
entity; in this case they denote the same entity.
8.1 Declarative Region
8.2 Scope of Declarations
8.3 Visibility
8.4 Use Clauses
8.5 Renaming Declarations
8.6 The Context of Overload Resolution --- The
Detailed Node Listing ---
8.1 Declarative Region
8.2 Scope of Declarations
8.3 Visibility
8.4 Use Clauses
8.5 Renaming Declarations
8.5.1 Object Renaming Declarations
8.5.2 Exception Renaming Declarations
8.5.3 Package Renaming Declarations
8.5.4 Subprogram Renaming Declarations
8.5.5 Generic Renaming Declarations
8.6 The Context of Overload Resolution
ΓòÉΓòÉΓòÉ 11.1. Declarative Region ΓòÉΓòÉΓòÉ
Static Semantics
1. For each of the following constructs, there is a portion of the program
text called its declarative region, within which nested declarations can
occur:
a. any declaration, other than that of an enumeration type, that is not
a completion of a previous declaration;
b. a block_statement;
c. a loop_statement;
d. an accept_statement;
e. an exception_handler.
1. The declarative region includes the text of the construct together with
additional text determined (recursively), as follows:
a. If a declaration is included, so is its completion, if any.
b. If the declaration of a library unit (including Standard -- see
10.1.1, is included, so are the declarations of any child units (and
their completions, by the previous rule). The child declarations
occur after the declaration.
c. If a body_stub is included, so is the corresponding subunit.
d. If a type_declaration is included, then so is a corresponding
record_representation_clause, if any.
1. The declarative region of a declaration is also called the declarative
region of any view or entity declared by the declaration.
2. A declaration occurs immediately within a declarative region if this
region is the innermost declarative region that encloses the declaration
(the immediately enclosing declarative region), not counting the
declarative region (if any) associated with the declaration itself.
3. A declaration is local to a declarative region if the declaration occurs
immediately within the declarative region. An entity is local to a
declarative region if the entity is declared by a declaration that is
local to the declarative region.
4. A declaration is global to a declarative region if the declaration occurs
immediately within another declarative region that encloses the
declarative region. An entity is global to a declarative region if the
entity is declared by a declaration that is global to the declarative
region.
NOTES
5. (1) The children of a parent library unit are inside the parent's
declarative region, even though they do not occur inside the parent's
declaration or body. This implies that one can use (for example) "P.Q" to
refer to a child of P whose defining name is Q, and that after "use P;" Q
can refer (directly) to that child.
6. (2) As explained above and in 10.1.1: ``Compilation Units - Library
Units'', all library units are descendants of Standard, and so are
contained in the declarative region of Standard. They are not inside the
declaration or body of Standard, but they are inside its declarative
region.
7. (3) For a declarative region that comes in multiple parts, the text of
the declarative region does not contain any text that might appear
between the parts. Thus, when a portion of a declarative region is said
to extend from one place to another in the declarative region, the
portion does not contain any text that might appear between the parts of
the declarative region.
ΓòÉΓòÉΓòÉ 11.2. Scope of Declarations ΓòÉΓòÉΓòÉ
1. For each declaration, the language rules define a certain portion of the
program text called the scope of the declaration. The scope of a
declaration is also called the scope of any view or entity declared by
the declaration. Within the scope of an entity, and only there, there are
places where it is legal to refer to the declared entity. These places
are defined by the rules of visibility and overloading.
Static Semantics
2. The immediate scope of a declaration is a portion of the declarative
region immediately enclosing the declaration. The immediate scope starts
at the beginning of the declaration, except in the case of an
overloadable declaration, in which case the immediate scope starts just
after the place where the profile of the callable entity is determined
(which is at the end of the _specification for the callable entity, or at
the end of the generic_instantiation if an instance). The immediate scope
extends to the end of the declarative region, with the following
exceptions:
a. The immediate scope of a library_item includes only its semantic
dependents.
b. The immediate scope of a declaration in the private part of a
library unit does not include the visible part of any public
descendant of that library unit.
1. The visible part of (a view of) an entity is a portion of the text of its
declaration containing declarations that are visible from outside. The
private part of (a view of) an entity that has a visible part contains
all declarations within the declaration of (the view of) the entity,
except those in the visible part; these are not visible from outside.
Visible and private parts are defined only for these kinds of entities:
callable entities, other program units, and composite types.
a. The visible part of a view of a callable entity is its profile.
b. The visible part of a composite type other than a task or protected
type consists of the declarations of all components declared
(explicitly or implicitly) within the type_declaration.
c. The visible part of a generic unit includes the generic_formal_part.
For a generic package, it also includes the first list of
basic_declarative_items of the package_specification. For a generic
subprogram, it also includes the profile.
d. The visible part of a package, task unit, or protected unit consists
of declarations in the program unit's declaration other than those
following the reserved word private, if any; see 7.1, and 12.7, for
packages, see 9.1, for task units, and 9.4, for protected units.
1. The scope of a declaration always contains the immediate scope of the
declaration. In addition, for a given declaration that occurs immediately
within the visible part of an outer declaration, or is a public child of
an outer declaration, the scope of the given declaration extends to the
end of the scope of the outer declaration, except that the scope of a
library_item includes only its semantic dependents.
2. The immediate scope of a declaration is also the immediate scope of the
entity or view declared by the declaration. Similarly, the scope of a
declaration is also the scope of the entity or view declared by the
declaration.
NOTES
3. (4) There are notations for denoting visible declarations that are not
directly visible. For example, parameter_specifications are in the
visible part of a subprogram_declaration so that they can be used in
named-notation calls appearing outside the called subprogram. For another
example, declarations of the visible part of a package can be denoted by
expanded names appearing outside the package, and can be made directly
visible by a use_clause.
ΓòÉΓòÉΓòÉ 11.3. Visibility ΓòÉΓòÉΓòÉ
1. The visibility rules, given below, determine which declarations are
visible and directly visible at each place within a program. The
visibility rules apply to both explicit and implicit declarations.
Static Semantics
2. A declaration is defined to be directly visible at places where a name
consisting of only an identifier or operator_symbol is sufficient to
denote the declaration; that is, no selected_component notation or
special context (such as preceding => in a named association) is
necessary to denote the declaration. A declaration is defined to be
visible wherever it is directly visible, as well as at other places where
some name (such as a selected_component) can denote the declaration.
3. The syntactic category direct_name is used to indicate contexts where
direct visibility is required. The syntactic category selector_name is
used to indicate contexts where visibility, but not direct visibility, is
required.
4. There are two kinds of direct visibility: immediate visibility and
use-visibility. A declaration is immediately visible at a place if it is
directly visible because the place is within its immediate scope. A
declaration is use-visible if it is directly visible because of a
use_clause, see 8.4. Both conditions can apply.
5. A declaration can be hidden, either from direct visibility, or from all
visibility, within certain parts of its scope. Where hidden from all
visibility, it is not visible at all (neither using a direct_name nor a
selector_name). Where hidden from direct visibility, only direct
visibility is lost; visibility using a selector_name is still possible.
6. Two or more declarations are overloaded if they all have the same
defining name and there is a place where they are all directly visible.
7. The declarations of callable entities (including enumeration literals)
are overloadable, meaning that overloading is allowed for them.
8. Two declarations are homographs if they have the same defining name, and,
if both are overloadable, their profiles are type conformant. An inner
declaration hides any outer homograph from direct visibility.
9. Two homographs are not generally allowed immediately within the same
declarative region unless one overrides the other (see Legality Rules
below). A declaration overrides another homograph that occurs immediately
within the same declarative region in the following cases:
a. An explicit declaration overrides an implicit declaration of a
primitive subprogram, regardless of which declaration occurs first;
b. The implicit declaration of an inherited operator overrides that of
a predefined operator;
c. An implicit declaration of an inherited subprogram overrides a
previous implicit declaration of an inherited subprogram.
d. For an implicit declaration of a primitive subprogram in a generic
unit, there is a copy of this declaration in an instance. However, a
whole new set of primitive subprograms is implicitly declared for
each type declared within the visible part of the instance. These
new declarations occur immediately after the type declaration, and
override the copied ones. The copied ones can be called only from
within the instance; the new ones can be called only from outside
the instance, although for tagged types, the body of a new one can
be executed by a call to an old one.
1. A declaration is visible within its scope, except where hidden from all
visibility, as follows:
a. An overridden declaration is hidden from all visibility within the
scope of the overriding declaration.
b. A declaration is hidden from all visibility until the end of the
declaration, except:
1. For a record type or record extension, the declaration is
hidden from all visibility only until the reserved word record;
2. For a package_declaration, task declaration, protected
declaration, generic_package_declaration, or subprogram_body,
the declaration is hidden from all visibility only until the
reserved word is of the declaration.
a. If the completion of a declaration is a declaration, then within the
scope of the completion, the first declaration is hidden from all
visibility. Similarly, a discriminant_specification or
parameter_specification is hidden within the scope of a
corresponding discriminant_specification or parameter_specification
of a corresponding completion, or of a corresponding
accept_statement.
b. The declaration of a library unit (including a
library_unit_renaming_declaration) is hidden from all visibility
except at places that are within its declarative region or within
the scope of a with_clause that mentions it. For each declaration or
renaming of a generic unit as a child of some parent generic
package, there is a corresponding declaration nested immediately
within each instance of the parent. Such a nested declaration is
hidden from all visibility except at places that are within the
scope of a with_clause that mentions the child.
1. A declaration with a defining_identifier or defining_operator_symbol is
immediately visible (and hence directly visible) within its immediate
scope except where hidden from direct visibility, as follows:
a. A declaration is hidden from direct visibility within the immediate
scope of a homograph of the declaration, if the homograph occurs
within an inner declarative region;
b. A declaration is also hidden from direct visibility where hidden
from all visibility.
Name Resolution Rules
1. A direct_name shall resolve to denote a directly visible declaration
whose defining name is the same as the direct_name. A selector_name shall
resolve to denote a visible declaration whose defining name is the same
as the selector_name.
2. These rules on visibility and direct visibility do not apply in a
context_clause, a parent_unit_name, or a pragma that appears at the place
of a compilation_unit. For those contexts, see the rules in 10.1.6:
``Environment-Level Visibility Rules''.
Legality Rules
3. An explicit declaration is illegal if there is a homograph occurring
immediately within the same declarative region that is visible at the
place of the declaration, and is not hidden from all visibility by the
explicit declaration. Similarly, the context_clause for a subunit is
illegal if it mentions (in a with_clause) some library unit, and there is
a homograph of the library unit that is visible at the place of the
corresponding stub, and the homograph and the mentioned library unit are
both declared immediately within the same declarative region. These rules
also apply to dispatching operations declared in the visible part of an
instance of a generic unit. However, they do not apply to other
overloadable declarations in an instance; such declarations may have type
conformant profiles in the instance, so long as the corresponding
declarations in the generic were not type conformant.
NOTES
4. (5) Visibility for compilation units follows from the definition of the
environment in 10.1.4, except that it is necessary to apply a with_clause
to obtain visibility to a library_unit_declaration or
library_unit_renaming_declaration.
5. (6) In addition to the visibility rules given above, the meaning of the
occurrence of a direct_name or selector_name at a given place in the text
can depend on the overloading rules, see 8.6.
6. (7) Not all contexts where an identifier, character_literal, or
operator_symbol are allowed require visibility of a corresponding
declaration. Contexts where visibility is not required are identified by
using one of these three syntactic categories directly in a syntax rule,
rather than using direct_name or selector_name.
ΓòÉΓòÉΓòÉ 11.4. Use Clauses ΓòÉΓòÉΓòÉ
1. A use_package_clause achieves direct visibility of declarations that
appear in the visible part of a package; a use_type_clause achieves
direct visibility of the primitive operators of a type.
Syntax
2.
use_clause ::= use_package_clause | use_type_clause
3.
use_package_clause ::= use package_name {, package_name};
4.
use_type_clause ::= use type subtype_mark {, subtype_mark};
Legality Rules
5. A package_name of a use_package_clause shall denote a package.
Static Semantics
6. For each use_clause, there is a certain region of text called the scope
of the use_clause. For a use_clause within a context_clause of a
library_unit_declaration or library_unit_renaming_declaration, the scope
is the entire declarative region of the declaration. For a use_clause
within a context_clause of a body, the scope is the entire body and any
subunits (including multiply nested subunits). The scope does not include
context_clauses themselves.
7. For a use_clause immediately within a declarative region, the scope is
the portion of the declarative region starting just after the use_clause
and extending to the end of the declarative region. However, the scope of
a use_clause in the private part of a library unit does not include the
visible part of any public descendant of that library unit.
8. For each package denoted by a package_name of a use_package_clause whose
scope encloses a place, each declaration that occurs immediately within
the declarative region of the package is potentially use-visible at this
place if the declaration is visible at this place. For each type T or
T'Class determined by a subtype_mark of a use_type_clause whose scope
encloses a place, the declaration of each primitive operator of type T is
potentially use-visible at this place if its declaration is visible at
this place.
9. A declaration is use-visible if it is potentially use-visible, except in
these naming-conflict cases:
a. A potentially use-visible declaration is not use-visible if the
place considered is within the immediate scope of a homograph of the
declaration.
b. Potentially use-visible declarations that have the same identifier
are not use-visible unless each of them is an overloadable
declaration.
Dynamic Semantics
1. The elaboration of a use_clause has no effect.
Examples
2. Example of a use clause in a context clause:
3.
with Ada.Calendar; use Ada;
4.
Example of a use type clause:
5.
use type Rational_Numbers.Rational; -- see 7.1
Two_Thirds: Rational_Numbers.Rational := 2/3;
ΓòÉΓòÉΓòÉ 11.5. Renaming Declarations ΓòÉΓòÉΓòÉ
1. A renaming_declaration declares another name for an entity, such as an
object, exception, package, subprogram, entry, or generic unit.
Alternatively, a subprogram_renaming_declaration can be the completion of
a previous subprogram_declaration.
Syntax
2.
renaming_declaration ::=
object_renaming_declaration
| exception_renaming_declaration
| package_renaming_declaration
| subprogram_renaming_declaration
| generic_renaming_declaration
Dynamic Semantics
3. The elaboration of a renaming_declaration evaluates the name that follows
the reserved word renames and thereby determines the view and entity
denoted by this name (the renamed view and renamed entity). A name that
denotes the renaming_declaration denotes (a new view of) the renamed
entity.
NOTES
4. (8) Renaming may be used to resolve name conflicts and to act as a
shorthand. Renaming with a different identifier or operator_symbol does
not hide the old name; the new name and the old name need not be visible
at the same places.
5. (9) A task or protected object that is declared by an explicit
object_declaration can be renamed as an object. However, a single task or
protected object cannot be renamed since the corresponding type is
anonymous (meaning it has no nameable subtypes). For similar reasons, an
object of an anonymous array or access type cannot be renamed.
6. (10) A subtype defined without any additional constraint can be used to
achieve the effect of renaming another subtype (including a task or
protected subtype) as in
7.
subtype Mode is Ada.Text_IO.File_Mode;
8.5.1 Object Renaming Declarations
8.5.2 Exception Renaming Declarations
8.5.3 Package Renaming Declarations
8.5.4 Subprogram Renaming Declarations
8.5.5 Generic Renaming Declarations
ΓòÉΓòÉΓòÉ 11.5.1. Object Renaming Declarations ΓòÉΓòÉΓòÉ
1. An object_renaming_declaration is used to rename an object.
Syntax
2.
object_renaming_declaration ::=
defining_identifier : subtype_mark renames object_name;
Name Resolution Rules
3. The type of the object_name shall resolve to the type determined by the
subtype_mark.
Legality Rules
4. The renamed entity shall be an object.
5. The renamed entity shall not be a subcomponent that depends on
discriminants of a variable whose nominal subtype is unconstrained,
unless this subtype is indefinite, or the variable is aliased. A slice of
an array shall not be renamed if this restriction disallows renaming of
the array.
Static Semantics
6. An object_renaming_declaration declares a new view of the renamed object
whose properties are identical to those of the renamed view. Thus, the
properties of the renamed object are not affected by the
renaming_declaration. In particular, its value and whether or not it is a
constant are unaffected; similarly, the constraints that apply to an
object are not affected by renaming (any constraint implied by the
subtype_mark of the object_renaming_declaration is ignored).
Examples
7. Example of renaming an object:
8.
declare
L : Person renames Leftmost_Person; -- see 3.10.1
begin
L.Age := L.Age + 1;
end;
ΓòÉΓòÉΓòÉ 11.5.2. Exception Renaming Declarations ΓòÉΓòÉΓòÉ
1. An exception_renaming_declaration is used to rename an exception.
Syntax
2.
exception_renaming_declaration ::=
defining_identifier : exception renames exception_name;
Legality Rules
3. The renamed entity shall be an exception.
Static Semantics
4. An exception_renaming_declaration declares a new view of the renamed
exception.
Examples
5. Example of renaming an exception:
6.
EOF : exception renames Ada.IO_Exceptions.End_Error;
-- see A.13
ΓòÉΓòÉΓòÉ 11.5.3. Package Renaming Declarations ΓòÉΓòÉΓòÉ
1. A package_renaming_declaration is used to rename a package.
Syntax
2.
package_renaming_declaration ::=
package defining_program_unit_name renames package_name;
Legality Rules
3. The renamed entity shall be a package.
Static Semantics
4. A package_renaming_declaration declares a new view of the renamed
package.
Examples
5. Example of renaming a package:
6.
package TM renames Table_Manager;
ΓòÉΓòÉΓòÉ 11.5.4. Subprogram Renaming Declarations ΓòÉΓòÉΓòÉ
1. A subprogram_renaming_declaration can serve as the completion of a
subprogram_declaration; such a renaming_declaration is called a
renaming-as-body. A subprogram_renaming_declaration that is not a
completion is called a renaming-as-declaration, and is used to rename a
subprogram (possibly an enumeration literal) or an entry.
Syntax
2.
subprogram_renaming_declaration ::=
subprogram_specification renames callable_entity_name;
Name Resolution Rules
3. The expected profile for the callable_entity_name is the profile given in
the subprogram_specification.
Legality Rules
4. The profile of a renaming-as-declaration shall be mode-conformant with
that of the renamed callable entity.
5. The profile of a renaming-as-body shall be subtype-conformant with that
of the renamed callable entity, and shall conform fully to that of the
declaration it completes. If the renaming-as-body completes that
declaration before the subprogram it declares is frozen, the subprogram
it declares takes its convention from the renamed subprogram; otherwise
the convention of the renamed subprogram shall not be Intrinsic.
6. A name that denotes a formal parameter of the subprogram_specification is
not allowed within the callable_entity_name.
Static Semantics
7. A renaming-as-declaration declares a new view of the renamed entity. The
profile of this new view takes its subtypes, parameter modes, and calling
convention from the original profile of the callable entity, while taking
the formal parameter names and default_expressions from the profile given
in the subprogram_renaming_declaration. The new view is a function or
procedure, never an entry.
Dynamic Semantics
8. For a call on a renaming of a dispatching subprogram that is overridden,
if the overriding occurred before the renaming, then the body executed is
that of the overriding declaration, even if the overriding declaration is
not visible at the place of the renaming; otherwise, the inherited or
predefined subprogram is called.
NOTES
9. (11) A procedure can only be renamed as a procedure. A function whose
defining_designator is either an identifier or an operator_symbol can be
renamed with either an identifier or an operator_symbol; for renaming as
an operator, the subprogram specification given in the
renaming_declaration is subject to the rules given in 6.6, for operator
declarations. Enumeration literals can be renamed as functions;
similarly, attribute_references that denote functions (such as references
to Succ and Pred) can be renamed as functions. An entry can only be
renamed as a procedure; the new name is only allowed to appear in
contexts that allow a procedure name. An entry of a family can be
renamed, but an entry family cannot be renamed as a whole.
10. (12) The operators of the root numeric types cannot be renamed because
the types in the profile are anonymous, so the corresponding
specifications cannot be written; the same holds for certain attributes,
such as Pos.
11. (13) Calls with the new name of a renamed entry are
procedure_call_statements and are not allowed at places where the syntax
requires an entry_call_statement in conditional_ and timed_entry_calls,
nor in an asynchronous_select; similarly, the Count attribute is not
available for the new name.
12. (14) The primitiveness of a renaming-as-declaration is determined by its
profile, and by where it occurs, as for any declaration of (a view of) a
subprogram; primitiveness is not determined by the renamed view. In order
to perform a dispatching call, the subprogram name has to denote a
primitive subprogram, not a non-primitive renaming of a primitive
subprogram.
Examples
13. Examples of subprogram renaming declarations:
14.
procedure My_Write(C : in Character) renames Pool(K).Write;
-- see 4.1.3
15.
function Real_Plus(Left, Right : Real ) return Real renames "+";
function Int_Plus (Left, Right : Integer) return Integer renames "+";
16.
function Rouge return Color renames Red; -- see 3.5.1
function Rot return Color renames Red;
function Rosso return Color renames Rouge;
17.
function Next(X : Color) return Color renames Color'Succ;
-- see 3.5.1
18. Example of a subprogram renaming declaration with new parameter names:
19.
function "*" (X,Y : Vector) return Real renames Dot_Product;
-- see 6.1
20. Example of a subprogram renaming declaration with a new default
expression:
21.
function Minimum(L : Link := Head) return Cell renames Min_Cell;
-- see 6.1
ΓòÉΓòÉΓòÉ 11.5.5. Generic Renaming Declarations ΓòÉΓòÉΓòÉ
A generic_renaming_declaration is used to rename a generic unit.
Syntax
1.
generic_renaming_declaration ::=
generic package defining_program_unit_name renames
generic_package_name;
| generic procedure defining_program_unit_name renames
generic_procedure_name;
| generic function defining_program_unit_name renames
generic_function_name;
Legality Rules
2. The renamed entity shall be a generic unit of the corresponding kind.
Static Semantics
3. A generic_renaming_declaration declares a new view of the renamed generic
unit.
NOTES
4. (15) Although the properties of the new view are the same as those of the
renamed view, the place where the generic_renaming_declaration occurs may
affect the legality of subsequent renamings and instantiations that
denote the generic_renaming_declaration, in particular if the renamed
generic unit is a library unit, see 10.1.1.
Examples
5. Example of renaming a generic unit:
6.
generic package Enum_IO renames Ada.Text_IO.Enumeration_IO;
-- see A.10.10
ΓòÉΓòÉΓòÉ 11.6. The Context of Overload Resolution ΓòÉΓòÉΓòÉ
1. Because declarations can be overloaded, it is possible for an occurrence
of a usage name to have more than one possible interpretation; in most
cases, ambiguity is disallowed. This clause describes how the possible
interpretations resolve to the actual interpretation.
2. Certain rules of the language (the Name Resolution Rules) are considered
``overloading rules''. If a possible interpretation violates an
overloading rule, it is assumed not to be the intended interpretation;
some other possible interpretation is assumed to be the actual
interpretation. On the other hand, violations of non-overloading rules do
not affect which interpretation is chosen; instead, they cause the
construct to be illegal. To be legal, there usually has to be exactly one
acceptable interpretation of a construct that is a ``complete context'',
not counting any nested complete contexts.
3. The syntax rules of the language and the visibility rules given in 8.3,
determine the possible interpretations. Most type checking rules (rules
that require a particular type, or a particular class of types, for
example) are overloading rules. Various rules for the matching of formal
and actual parameters are overloading rules.
Name Resolution Rules
4. Overload resolution is applied separately to each complete context, not
counting inner complete contexts. Each of the following constructs is a
complete context:
a. A context_item.
b. declarative_item or declaration.
c. A statement.
d. A pragma_argument_association.
e. The expression of a case_statement.
1. An (overall) interpretation of a complete context embodies its meaning,
and includes the following information about the constituents of the
complete context, not including constituents of inner complete contexts:
a. for each constituent of the complete context, to which syntactic
categories it belongs, and by which syntax rules; and
b. for each usage name, which declaration it denotes (and, therefore,
which view and which entity it denotes); and
c. for a complete context that is a declarative_item, whether or not it
is a completion of a declaration, and (if so) which declaration it
completes.
1. A possible interpretation is one that obeys the syntax rules and the
visibility rules. An acceptable interpretation is a possible
interpretation that obeys the overloading rules, that is, those rules
that specify an expected type or expected profile, or specify how a
construct shall resolve or be interpreted.
2. The interpretation of a constituent of a complete context is determined
from the overall interpretation of the complete context as a whole. Thus,
for example, ``interpreted as a function_call,'' means that the
construct's interpretation says that it belongs to the syntactic category
function_call.
3. Each occurrence of a usage name denotes the declaration determined by its
interpretation. It also denotes the view declared by its denoted
declaration, except in the following cases:
a. If a usage name appears within the declarative region of a
type_declaration and denotes that same type_declaration, then it
denotes the current instance of the type (rather than the type
itself). The current instance of a type is the object or value of
the type that is associated with the execution that evaluates the
usage name.
b. If a usage name appears within the declarative region of a
generic_declaration (but not within its generic_formal_part) and it
denotes that same generic_declaration, then it denotes the current
instance of the generic unit (rather than the generic unit itself).
See also 12.3.
1. A usage name that denotes a view also denotes the entity of that view.
2. The expected type for a given expression, name, or other construct
determines, according to the type resolution rules given below, the types
considered for the construct during overload resolution. The type
resolution rules provide support for class-wide programming, universal
numeric literals, dispatching operations, and anonymous access types:
a. If a construct is expected to be of any type in a class of types, or
of the universal or class-wide type for a class, then the type of
the construct shall resolve to a type in that class or to a
universal type that covers the class.
b. If the expected type for a construct is a specific type T, then the
type of the construct shall resolve either to T, or:
1. to T'Class; or
2. to a universal type that covers T; or
3. when T is an anonymous access type, see 3.10, with designated
type D, to an access-to-variable type whose designated type is
D'Class or is covered by D.
1. In certain contexts, such as in a subprogram_renaming_declaration, the
Name Resolution Rules define an expected profile for a given name; in
such cases, the name shall resolve to the name of a callable entity whose
profile is type conformant with the expected profile.
Legality Rules
2. When the expected type for a construct is required to be a single type in
a given class, the type expected for the construct shall be determinable
solely from the context in which the construct appears, excluding the
construct itself, but using the requirement that it be in the given
class; the type of the construct is then this single expected type.
Furthermore, the context shall not be one that expects any type in some
class that contains types of the given class; in particular, the
construct shall not be the operand of a type_conversion.
3. A complete context shall have at least one acceptable interpretation; if
there is exactly one, then that one is chosen.
4. There is a preference for the primitive operators (and ranges) of the
root numeric types root_integer and root_real. In particular, if two
acceptable interpretations of a constituent of a complete context differ
only in that one is for a primitive operator (or range) of the type
root_integer or root_real, and the other is not, the interpretation using
the primitive operator (or range) of the root numeric type is preferred.
5. For a complete context, if there is exactly one overall acceptable
interpretation where each constituent's interpretation is the same as or
preferred (in the above sense) over those in all other overall acceptable
interpretations, then that one overall acceptable interpretation is
chosen. Otherwise, the complete context is ambiguous.
6. A complete context other than a pragma_argument_association shall not be
ambiguous.
7. A complete context that is a pragma_argument_association is allowed to be
ambiguous (unless otherwise specified for the particular pragma), but
only if every acceptable interpretation of the pragma argument is as a
name that statically denotes a callable entity. Such a name denotes all
of the declarations determined by its interpretations, and all of the
views declared by these declarations.
NOTES
8. (16) If a usage name has only one acceptable interpretation, then it
denotes the corresponding entity. However, this does not mean that the
usage name is necessarily legal since other requirements exist which are
not considered for overload resolution; for example, the fact that an
expression is static, whether an object is constant, mode and subtype
conformance rules, freezing rules, order of elaboration, and so on.
9. Similarly, subtypes are not considered for overload resolution (the
violation of a constraint does not make a program illegal but raises an
exception during program execution).
ΓòÉΓòÉΓòÉ 12. Tasks and Synchronization ΓòÉΓòÉΓòÉ
1. The execution of an Ada program consists of the execution of one or more
tasks. Each task represents a separate thread of control that proceeds
independently and concurrently between the points where it interacts with
other tasks. The various forms of task interaction are described in this
section, and include:
a. the activation and termination of a task;
b. a call on a protected subprogram of a protected object, providing
exclusive read-write access, or concurrent read-only access to
shared data;
c. a call on an entry, either of another task, allowing for synchronous
communication with that task, or of a protected object, allowing for
asynchronous communication with one or more other tasks using that
same protected object;
d. a timed operation, including a simple delay statement, a timed entry
call or accept, or a timed asynchronous select statement (see next
item);
e. an asynchronous transfer of control as part of an asynchronous
select statement, where a task stops what it is doing and begins
execution at a different point in response to the completion of an
entry call or the expiration of a delay;
f. an abort statement, allowing one task to cause the termination of
another task.
1. In addition, tasks can communicate indirectly by reading and updating
(unprotected) shared variables, presuming the access is properly
synchronized through some other kind of task interaction.
Static Semantics
2. The properties of a task are defined by a corresponding task declaration
and task_body, which together define a program unit called a task unit.
Dynamic Semantics
3. Over time, tasks proceed through various states. A task is initially
inactive; upon activation, and prior to its termination it is either
blocked (as part of some task interaction) or ready to run. While ready,
a task competes for the available execution resources that it requires to
run.
NOTES
4. (1) Concurrent task execution may be implemented on multicomputers,
multiprocessors, or with interleaved execution on a single physical
processor. On the other hand, whenever an implementation can determine
that the required semantic effects can be achieved when parts of the
execution of a given task are performed by different physical processors
acting in parallel, it may choose to perform them in this way.
9.1 Task Units and Task Objects
9.2 Task Execution - Task Activation
9.3 Task Dependence - Termination of Tasks
9.4 Protected Units and Protected Objects
9.5 Intertask Communication
9.6 Delay Statements, Duration, and Time
9.7 Select Statements
9.8 Abort of a Task - Abort of a Sequence of
Statements
9.9 Task and Entry Attributes
9.10 Shared Variables
9.11 Example of Tasking and Synchronization --- The
Detailed Node Listing ---
9.1 Task Units and Task Objects
9.2 Task Execution - Task Activation
9.3 Task Dependence - Termination of Tasks
9.4 Protected Units and Protected Objects
9.5 Intertask Communication
9.5.1 Protected Subprograms and Protected Actions
9.5.2 Entries and Accept Statements
9.5.3 Entry Calls
9.5.4 Requeue Statements
9.6 Delay Statements, Duration, and Time
9.7 Select Statements
9.7.1 Selective Accept
9.7.2 Timed Entry Calls
9.7.3 Conditional Entry Calls
9.7.4 Asynchronous Transfer of Control
9.8 Abort of a Task - Abort of a Sequence of
Statements
9.9 Task and Entry Attributes
9.10 Shared Variables
9.11 Example of Tasking and Synchronization
ΓòÉΓòÉΓòÉ 12.1. Task Units and Task Objects ΓòÉΓòÉΓòÉ
1. A task unit is declared by a task declaration, which has a corresponding
task_body. A task declaration may be a task_type_declaration, in which
case it declares a named task type; alternatively, it may be a
single_task_declaration, in which case it defines an anonymous task type,
as well as declaring a named task object of that type.
Syntax
2.
task_type_declaration ::=
task type defining_identifier [known_discriminant_part]
[is task_definition];
3.
single_task_declaration ::=
task defining_identifier [is task_definition];
4.
task_definition ::=
{task_item}
[ private
{task_item}]
end [task_identifier]
5.
task_item ::= entry_declaration | representation_clause
6.
task_body ::=
task body defining_identifier is
declarative_part
begin
handled_sequence_of_statements
end [task_identifier];
a. If a task_identifier appears at the end of a task_definition or
task_body, it shall repeat the defining_identifier.
Legality Rules
1. A task declaration requires a completion, which shall be a task_body, and
every task_body shall be the completion of some task declaration.
Static Semantics
2. A task_definition defines a task type and its first subtype. The first
list of task_items of a task_definition, together with the
known_discriminant_part, if any, is called the visible part of the task
unit. The optional list of task_items after the reserved word private is
called the private part of the task unit.
Dynamic Semantics
3. The elaboration of a task declaration elaborates the task_definition. The
elaboration of a single_task_declaration also creates an object of an
(anonymous) task type.
4. The elaboration of a task_definition creates the task type and its first
subtype; it also includes the elaboration of the entry_declarations in
the given order.
5. As part of the initialization of a task object, any
representation_clauses and any per-object constraints associated with
entry_declarations of the corresponding task_definition are elaborated in
the given order.
6. The elaboration of a task_body has no effect other than to establish that
tasks of the type can from then on be activated without failing the
Elaboration_Check.
7. The execution of a task_body is invoked by the activation of a task of
the corresponding type, see 9.2.
8. The content of a task object of a given task type includes:
a. The values of the discriminants of the task object, if any;
b. An entry queue for each entry of the task object;
c. A representation of the state of the associated task.
NOTES
1. (2) Within the declaration or body of a task unit, the name of the task
unit denotes the current instance of the unit, see 8.6, rather than the
first subtype of the corresponding task type (and thus the name cannot be
used as a subtype_mark).
2. (3) The notation of a selected_component can be used to denote a
discriminant of a task, see 4.1.3. Within a task unit, the name of a
discriminant of the task type denotes the corresponding discriminant of
the current instance of the unit.
3. (4) A task type is a limited type, see 7.5, and hence has neither an
assignment operation nor predefined equality operators. If an application
needs to store and exchange task identities, it can do so by defining an
access type designating the corresponding task objects and by using
access values for identification purposes. Assignment is available for
such an access type as for any access type. Alternatively, if the
implementation supports the Systems Programming Annex, the Identity
attribute can be used for task identification, see C.7.
Examples
4. Examples of declarations of task types:
5.
task type Server is
entry Next_Work_Item(WI : in Work_Item);
entry Shut_Down;
end Server;
6.
task type Keyboard_Driver(ID : Keyboard_ID := New_ID) is
entry Read (C : out Character);
entry Write(C : in Character);
end Keyboard_Driver;
7. Examples of declarations of single tasks:
8.
task Controller is
entry Request(Level)(D : Item); -- a family of entries
end Controller;
9.
task Parser is
entry Next_Lexeme(L : in Lexical_Element);
entry Next_Action(A : out Parser_Action);
end;
10.
task User; -- has no entries
11. Examples of task objects:
12.
Agent : Server;
Teletype : Keyboard_Driver(TTY_ID);
Pool : array(1 ┬╖┬╖ 10) of Keyboard_Driver;
13. Example of access type designating task objects:
14.
type Keyboard is access Keyboard_Driver;
Terminal : Keyboard := new Keyboard_Driver(Term_ID);
ΓòÉΓòÉΓòÉ 12.2. Task Execution - Task Activation ΓòÉΓòÉΓòÉ
Dynamic Semantics
1. The execution of a task of a given task type consists of the execution of
the corresponding task_body. The initial part of this execution is called
the activation of the task; it consists of the elaboration of the
declarative_part of the task_body. Should an exception be propagated by
the elaboration of its declarative_part, the activation of the task is
defined to have failed, and it becomes a completed task.
2. A task object (which represents one task) can be created either as part
of the elaboration of an object_declaration occurring immediately within
some declarative region, or as part of the evaluation of an allocator.
All tasks created by the elaboration of object_declarations of a single
declarative region (including subcomponents of the declared objects) are
activated together. Similarly, all tasks created by the evaluation of a
single allocator are activated together. The activation of a task is
associated with the innermost allocator or object_declaration that is
responsible for its creation.
3. For tasks created by the elaboration of object_declarations of a given
declarative region, the activations are initiated within the context of
the handled_sequence_of_statements (and its associated exception_handlers
if any -- see 11.2, just prior to executing the statements of the
_sequence. For a package without an explicit body or an explicit
handled_sequence_of_statements, an implicit body or an implicit
null_statement is assumed, as defined in 7.2.
4. For tasks created by the evaluation of an allocator, the activations are
initiated as the last step of evaluating the allocator, after completing
any initialization for the object created by the allocator, and prior to
returning the new access value.
5. The task that created the new tasks and initiated their activations (the
activator) is blocked until all of these activations complete
(successfully or not). Once all of these activations are complete, if the
activation of any of the tasks has failed (due to the propagation of an
exception), Tasking_Error is raised in the activator, at the place at
which it initiated the activations. Otherwise, the activator proceeds
with its execution normally. Any tasks that are aborted prior to
completing their activation are ignored when determining whether to raise
Tasking_Error.
6. Should the task that created the new tasks never reach the point where it
would initiate the activations (due to an abort or the raising of an
exception), the newly created tasks become terminated and are never
activated.
NOTES
7. (5) An entry of a task can be called before the task has been activated.
8. (6) If several tasks are activated together, the execution of any of
these tasks need not await the end of the activation of the other tasks.
9. (7) A task can become completed during its activation either because of
an exception or because it is aborted, see 9.8.
Examples
10. Example of task activation:
11.
procedure P is
A, B : Server; -- elaborate the task objects A, B
C : Server; -- elaborate the task object C
begin
-- the tasks A, B, C are activated together
-- before the first statement
┬╖┬╖┬╖
end;
ΓòÉΓòÉΓòÉ 12.3. Task Dependence - Termination of Tasks ΓòÉΓòÉΓòÉ
Dynamic Semantics
1. Each task (other than an environment task -- see 10.2, depends on one or
more masters, see 7.6.1, as follows:
a. If the task is created by the evaluation of an allocator for a given
access type, it depends on each master that includes the elaboration
of the declaration of the ultimate ancestor of the given access
type.
b. If the task is created by the elaboration of an object_declaration,
it depends on each master that includes this elaboration.
1. Furthermore, if a task depends on a given master, it is defined to depend
on the task that executes the master, and (recursively) on any master of
that task.
2. A task is said to be completed when the execution of its corresponding
task_body is completed. A task is said to be terminated when any
finalization of the task_body has been performed, see 7.6.1. The first
step of finalizing a master (including a task_body) is to wait for the
termination of any tasks dependent on the master. The task executing the
master is blocked until all the dependents have terminated. Any remaining
finalization is then performed and the master is left.
3. Completion of a task (and the corresponding task_body) can occur when the
task is blocked at a select_statement with an an open
terminate_alternative, see 9.7.1, the open terminate_alternative is
selected if and only if the following conditions are satisfied:
a. The task depends on some completed master;
b. Each task that depends on the master considered is either already
terminated or similarly blocked at a select_statement with an open
terminate_alternative.
1. When both conditions are satisfied, the task considered becomes
completed, together with all tasks that depend on the master considered
that are not yet completed.
NOTES
2. (8) The full view of a limited private type can be a task type, or can
have subcomponents of a task type. Creation of an object of such a type
creates dependences according to the full type.
3. (9) An object_renaming_declaration defines a new view of an existing
entity and hence creates no further dependence.
4. (10) The rules given for the collective completion of a group of tasks
all blocked on select_statements with open terminate_alternatives ensure
that the collective completion can occur only when there are no remaining
active tasks that could call one of the tasks being collectively
completed.
5. (11) If two or more tasks are blocked on select_statements with open
terminate_alternatives, and become completed collectively, their
finalization actions proceed concurrently.
6. (12) The completion of a task can occur due to any of the following:
a. the raising of an exception during the elaboration of the
declarative_part of the corresponding task_body;
b. the completion of the handled_sequence_of_statements of the
corresponding task_body;
c. the selection of an open terminate_alternative of a select_statement
in the corresponding task_body;
d. the abort of the task.
Examples
1. Example of task dependence:
2.
declare
type Global is access Server; -- see 9.1
A, B : Server;
G : Global;
begin
-- activation of A and B
declare
type Local is access Server;
X : Global := new Server; -- activation of X.all
L : Local := new Server; -- activation of L.all
C : Server;
begin
-- activation of C
G := X; -- both G and X designate the same task object
┬╖┬╖┬╖
end; -- await termination of C and L.all (but not X.all)
┬╖┬╖┬╖
end; -- await termination of A, B, and G.all
ΓòÉΓòÉΓòÉ 12.4. Protected Units and Protected Objects ΓòÉΓòÉΓòÉ
1. A protected object provides coordinated access to shared data, through
calls on its visible protected operations, which can be protected
subprograms or protected entries. A protected unit is declared by a
protected declaration, which has a corresponding protected_body. A
protected declaration may be a protected_type_declaration, in which case
it declares a named protected type; alternatively, it may be a
single_protected_declaration, in which case it defines an anonymous
protected type, as well as declaring a named protected object of that
type.
Syntax
2.
protected_type_declaration ::=
protected type defining_identifier [known_discriminant_part] is
protected_definition;
3.
single_protected_declaration ::=
protected defining_identifier is protected_definition;
4.
protected_definition ::=
{ protected_operation_declaration }
[ private
{ protected_element_declaration } ]
end [protected_identifier]
5.
protected_operation_declaration ::=
subprogram_declaration
| entry_declaration
| representation_clause
6.
protected_element_declaration ::=
protected_operation_declaration | component_declaration
7.
protected_body ::=
protected body defining_identifier is
{ protected_operation_item }
end [protected_identifier];
8.
protected_operation_item ::=
subprogram_declaration
| subprogram_body
| entry_body
| representation_clause
a. If a protected_identifier appears at the end of a
protected_definition or protected_body, it shall repeat the
defining_identifier.
Legality Rules
1. A protected declaration requires a completion, which shall be a
protected_body, and every protected_body shall be the completion of some
protected declaration.
Static Semantics
2. A protected_definition defines a protected type and its first subtype.
The list of protected_operation_declarations of a protected_definition,
together with the known_discriminant_part, if any, is called the visible
part of the protected unit. The optional list of
protected_element_declarations after the reserved word private is called
the private part of the protected unit.
Dynamic Semantics
3. The elaboration of a protected declaration elaborates the
protected_definition. The elaboration of a single_protected_declaration
also creates an object of an (anonymous) protected type.
4. The elaboration of a protected_definition creates the protected type and
its first subtype; it also includes the elaboration of the
component_declarations and protected_operation_declarations in the given
order.
5. As part of the initialization of a protected object, any per-object
constraints, see 3.8, are elaborated.
6. The elaboration of a protected_body has no other effect than to establish
that protected operations of the type can from then on be called without
failing the Elaboration_Check.
7. The content of an object of a given protected type includes:
a. The values of the components of the protected object, including
(implicitly) an entry queue for each entry declared for the
protected object;
b. A representation of the state of the execution resource associated
with the protected object (one such resource is associated with each
protected object).
1. The execution resource associated with a protected object has to be
acquired to read or update any components of the protected object; it can
be acquired (as part of a protected action -- see 9.5.1, either for
concurrent read-only access, or for exclusive read-write access.
2. As the first step of the finalization of a protected object, each call
remaining on any entry queue of the object is removed from its queue and
Program_Error is raised at the place of the corresponding
entry_call_statement.
NOTES
3. (13) Within the declaration or body of a protected unit, the name of the
protected unit denotes the current instance of the unit, see 8.6, rather
than the first subtype of the corresponding protected type (and thus the
name cannot be used as a subtype_mark).
4. (14) A selected_component can be used to denote a discriminant of a
protected object, see 4.1.3. Within a protected unit, the name of a
discriminant of the protected type denotes the corresponding discriminant
of the current instance of the unit.
5. (15) A protected type is a limited type, see 7.5, and hence has neither
an assignment operation nor predefined equality operators.
6. (16) The bodies of the protected operations given in the protected_body
define the actions that take place upon calls to the protected
operations.
7. (17) The declarations in the private part are only visible within the
private part and the body of the protected unit.
Examples
8. Example of declaration of protected type and corresponding body:
9.
protected type Resource is
entry Seize;
procedure Release;
private
Busy : Boolean := False;
end Resource;
10.
protected body Resource is
entry Seize when not Busy is
begin
Busy := True;
end Seize;
11.
procedure Release is
begin
Busy := False;
end Release;
end Resource;
12. Example of a single protected declaration and corresponding body:
13.
protected Shared_Array is
-- Index, Item, and Item_Array are global types
function Component (N : in Index) return Item;
procedure Set_Component(N : in Index; E : in Item);
private
Table : Item_Array(Index) := (others => Null_Item);
end Shared_Array;
14.
protected body Shared_Array is
function Component(N : in Index) return Item is
begin
return Table(N);
end Component;
15.
procedure Set_Component(N : in Index; E : in Item) is
begin
Table(N) := E;
end Set_Component;
end Shared_Array;
16. Examples of protected objects:
17.
Control : Resource;
Flags : array(1 ┬╖┬╖ 100) of Resource;
ΓòÉΓòÉΓòÉ 12.5. Intertask Communication ΓòÉΓòÉΓòÉ
1. The primary means for intertask communication is provided by calls on
entries and protected subprograms. Calls on protected subprograms allow
coordinated access to shared data objects. Entry calls allow for blocking
the caller until a given condition is satisfied (namely, that the
corresponding entry is open -- see 9.5.3.), and then communicating data
or control information directly with another task or indirectly via a
shared protected object.
Static Semantics
2. Any call on an entry or on a protected subprogram identifies a target
object for the operation, which is either a task (for an entry call) or a
protected object (for an entry call or a protected subprogram call). The
target object is considered an implicit parameter to the operation, and
is determined by the operation name (or prefix) used in the call on the
operation, as follows:
a. If it is a direct_name or expanded name that denotes the declaration
(or body) of the operation, then the target object is implicitly
specified to be the current instance of the task or protected unit
immediately enclosing the operation; such a call is defined to be an
internal call;
b. If it is a selected_component that is not an expanded name, then the
target object is explicitly specified to be the task or protected
object denoted by the prefix of the name; such a call is defined to
be an external call;
c. If the name or prefix is a dereference (implicit or explicit) of an
access-to-protected-subprogram value, then the target object is
determined by the prefix of the Access attribute_reference that
produced the access value originally, and the call is defined to be
an external call;
d. If the name or prefix denotes a subprogram_renaming_declaration,
then the target object is as determined by the name of the renamed
entity.
1. A corresponding definition of target object applies to a
requeue_statement, see 9.5.4, with a corresponding distinction between an
internal requeue and an external requeue.
Dynamic Semantics
2. Within the body of a protected operation, the current instance (see 8.6)
of the immediately enclosing protected unit is determined by the target
object specified (implicitly or explicitly) in the call (or requeue) on
the protected operation.
3. Any call on a protected procedure or entry of a target protected object
is defined to be an update to the object, as is a requeue on such an
entry.
9.5.1 Protected Subprograms and Protected Actions
9.5.2 Entries and Accept Statements
9.5.3 Entry Calls
9.5.4 Requeue Statements
ΓòÉΓòÉΓòÉ 12.5.1. Protected Subprograms and Protected Actions ΓòÉΓòÉΓòÉ
1. A protected subprogram is a subprogram declared immediately within a
protected_definition. Protected procedures provide exclusive read-write
access to the data of a protected object; protected functions provide
concurrent read-only access to the data.
Static Semantics
2. Within the body of a protected function (or a function declared
immediately within a protected_body), the current instance of the
enclosing protected unit is defined to be a constant (that is, its
subcomponents may be read but not updated). Within the body of a
protected procedure (or a procedure declared immediately within a
protected_body), and within an entry_body, the current instance is
defined to be a variable (updating is permitted).
Dynamic Semantics
3. For the execution of a call on a protected subprogram, the evaluation of
the name or prefix and of the parameter associations, and any assigning
back of in out or out parameters, proceeds as for a normal subprogram
call, see 6.4. If the call is an internal call, see 9.5, the body of the
subprogram is executed as for a normal subprogram call. If the call is an
external call, then the body of the subprogram is executed as part of a
new protected action on the target protected object; the protected action
completes after the body of the subprogram is executed. A protected
action can also be started by an entry call, see 9.5.3.
4. A new protected action is not started on a protected object while another
protected action on the same protected object is underway, unless both
actions are the result of a call on a protected function. This rule is
expressible in terms of the execution resource associated with the
protected object:
a. Starting a protected action on a protected object corresponds to
acquiring the execution resource associated with the protected
object, either for concurrent read-only access if the protected
action is for a call on a protected function, or for exclusive
read-write access otherwise;
b. Completing the protected action corresponds to releasing the
associated execution resource.
1. After performing an operation on a protected object other than a call on
a protected function, but prior to completing the associated protected
action, the entry queues (if any) of the protected object are serviced
(see 9.5.3).
Bounded (Run-Time) Errors
2. During a protected action, it is a bounded error to invoke an operation
that is potentially blocking. The following are defined to be potentially
blocking operations:
a. a select_statement;
b. an accept_statement;
c. an entry_call_statement;
d. a delay_statement;
e. an abort_statement;
f. task creation or activation;
g. an external call on a protected subprogram (or an external requeue)
with the same target object as that of the protected action;
h. a call on a subprogram whose body contains a potentially blocking
operation.
1. If the bounded error is detected, Program_Error is raised. If not
detected, the bounded error might result in deadlock or a (nested)
protected action on the same target object.
2. Certain language-defined subprograms are potentially blocking. In
particular, the subprograms of the language-defined input-output packages
that manipulate files (implicitly or explicitly) are potentially
blocking. Other potentially blocking subprograms are identified where
they are defined. When not specified as potentially blocking, a
language-defined subprogram is nonblocking.
NOTES
3. (18) If two tasks both try to start a protected action on a protected
object, and at most one is calling a protected function, then only one of
the tasks can proceed. Although the other task cannot proceed, it is not
considered blocked, and it might be consuming processing resources while
it awaits its turn. There is no language-defined ordering or queuing
presumed for tasks competing to start a protected action -- on a
multiprocessor such tasks might use busy-waiting; for monoprocessor
considerations, see D.3: ``Priority Ceiling Locking''.
4. (19) The body of a protected unit may contain declarations and bodies for
local subprograms. These are not visible outside the protected unit.
5. (20) The body of a protected function can contain internal calls on other
protected functions, but not protected procedures, because the current
instance is a constant. On the other hand, the body of a protected
procedure can contain internal calls on both protected functions and
procedures.
6. (21) From within a protected action, an internal call on a protected
subprogram, or an external call on a protected subprogram with a
different target object is not considered a potentially blocking
operation.
Examples
7. Examples of protected subprogram calls, see 9.4
8.
Shared_Array.Set_Component(N, E);
E := Shared_Array.Component(M);
Control.Release;
ΓòÉΓòÉΓòÉ 12.5.2. Entries and Accept Statements ΓòÉΓòÉΓòÉ
1. Entry_declarations, with the corresponding entry_bodies or
accept_statements, are used to define potentially queued operations on
tasks and protected objects.
Syntax
2.
entry_declaration ::=
entry defining_identifier [(discrete_subtype_definition)]
parameter_profile;
3.
accept_statement ::=
accept entry_direct_name [(entry_index)] parameter_profile
[do handled_sequence_of_statements
end [entry_identifier]];
4.
entry_index ::= expression
5.
entry_body ::=
entry defining_identifier entry_body_formal_part entry_barrier is
declarative_part
begin
handled_sequence_of_statements
end [entry_identifier];
6.
entry_body_formal_part ::=
[(entry_index_specification)] parameter_profile
7.
entry_barrier ::= when condition
8.
entry_index_specification ::=
for defining_identifier in discrete_subtype_definition
a. If an entry_identifier appears at the end of an accept_statement, it
shall repeat the entry_direct_name. If an entry_identifier appears
at the end of an entry_body, it shall repeat the
defining_identifier.
b. An entry_declaration is allowed only in a protected or task
declaration.
Name Resolution Rules
1. In an accept_statement, the expected profile for the entry_direct_name is
that of the entry_declaration; the expected type for an entry_index is
that of the subtype defined by the discrete_subtype_definition of the
corresponding entry_declaration.
2. Within the handled_sequence_of_statements of an accept_statement, if a
selected_component has a prefix that denotes the corresponding
entry_declaration, then the entity denoted by the prefix is the
accept_statement, and the selected_component is interpreted as an
expanded name, see 4.1.3, the selector_name of the selected_component has
to be the identifier for some formal parameter of the accept_statement.
Legality Rules
3. An entry_declaration in a task declaration shall not contain a
specification for an access parameter, see 3.10.
4. For an accept_statement, the innermost enclosing body shall be a
task_body, and the entry_direct_name shall denote an entry_declaration in
the corresponding task declaration; the profile of the accept_statement
shall conform fully to that of the corresponding entry_declaration. An
accept_statement shall have a parenthesized entry_index if and only if
the corresponding entry_declaration has a discrete_subtype_definition.
5. An accept_statement shall not be within another accept_statement that
corresponds to the same entry_declaration, nor within an
asynchronous_select inner to the enclosing task_body.
6. An entry_declaration of a protected unit requires a completion, which
shall be an entry_body, and every entry_body shall be the completion of
an entry_declaration of a protected unit. The profile of the entry_body
shall conform fully to that of the corresponding declaration.
7. An entry_body_formal_part shall have an entry_index_specification if and
only if the corresponding entry_declaration has a
discrete_subtype_definition. In this case, the
discrete_subtype_definitions of the entry_declaration and the
entry_index_specification shall fully conform to one another (see 6.3.1).
8. A name that denotes a formal parameter of an entry_body is not allowed
within the entry_barrier of the entry_body.
Static Semantics
9. The parameter modes defined for parameters in the parameter_profile of an
entry_declaration are the same as for a subprogram_declaration and have
the same meaning, see 6.2.
10. An entry_declaration with a discrete_subtype_definition, see 3.6,
declares a family of distinct entries having the same profile, with one
such entry for each value of the entry index subtype defined by the
discrete_subtype_definition. A name for an entry of a family takes the
form of an indexed_component, where the prefix denotes the
entry_declaration for the family, and the index value identifies the
entry within the family. The term single entry is used to refer to any
entry other than an entry of an entry family.
11. In the entry_body for an entry family, the entry_index_specification
declares a named constant whose subtype is the entry index subtype
defined by the corresponding entry_declaration; the value of the named
entry index identifies which entry of the family was called.
Dynamic Semantics
12. For the elaboration of an entry_declaration for an entry family, if the
discrete_subtype_definition contains no per-object expressions (see 3.8)
then the discrete_subtype_definition is elaborated. Otherwise, the
elaboration of the entry_declaration consists of the evaluation of any
expression of the discrete_subtype_definition that is not a per-object
expression (or part of one). The elaboration of an entry_declaration for
a single entry has no effect.
13. The actions to be performed when an entry is called are specified by the
corresponding accept_statements (if any) for an entry of a task unit, and
by the corresponding entry_body for an entry of a protected unit.
14. For the execution of an accept_statement, the entry_index, if any, is
first evaluated and converted to the entry index subtype; this index
value identifies which entry of the family is to be accepted. Further
execution of the accept_statement is then blocked until a caller of the
corresponding entry is selected, see 9.5.3, whereupon the
handled_sequence_of_statements, if any, of the accept_statement is
executed, with the formal parameters associated with the corresponding
actual parameters of the selected entry call. Upon completion of the
handled_sequence_of_statements, the accept_statement completes and is
left. When an exception is propagated from the
handled_sequence_of_statements of an accept_statement, the same exception
is also raised by the execution of the corresponding
entry_call_statement.
15. The above interaction between a calling task and an accepting task is
called a rendezvous. After a rendezvous, the two tasks continue their
execution independently.
16. An entry_body is executed when the condition of the entry_barrier
evaluates to True and a caller of the corresponding single entry, or
entry of the corresponding entry family, has been selected (see 9.5.3).
For the execution of the entry_body, the declarative_part of the
entry_body is elaborated, and the handled_sequence_of_statements of the
body is executed, as for the execution of a subprogram_body. The value of
the named entry index, if any, is determined by the value of the entry
index specified in the entry_name of the selected entry call (or
intermediate requeue_statement -- see 9.5.4.
NOTES
17. (22) A task entry has corresponding accept_statements (zero or more),
whereas a protected entry has a corresponding entry_body (exactly one).
18. (23) A consequence of the rule regarding the allowed placements of
accept_statements is that a task can execute accept_statements only for
its own entries.
19. (24) A return_statement, see 6.5, or a requeue_statement (see 9.5.4) may
be used to complete the execution of an accept_statement or an
entry_body.
20. (25) The condition in the entry_barrier may reference anything visible
except the formal parameters of the entry. This includes the entry index
(if any), the components (including discriminants) of the protected
object, the Count attribute of an entry of that protected object, and
data global to the protected unit.
21. The restriction against referencing the formal parameters within an
entry_barrier ensures that all calls of the same entry see the same
barrier value. If it is necessary to look at the parameters of an entry
call before deciding whether to handle it, the entry_barrier can be
``when True'' and the caller can be requeued (on some private entry) when
its parameters indicate that it cannot be handled immediately.
Examples
22. Examples of entry declarations:
23.
entry Read(V : out Item);
entry Seize;
entry Request(Level)(D : Item); -- a family of entries
24. Examples of accept statements:
25.
accept Shut_Down;
26.
accept Read(V : out Item) do
V := Local_Item;
end Read;
27.
accept Request(Low)(D : Item) do
┬╖┬╖┬╖
end Request;
ΓòÉΓòÉΓòÉ 12.5.3. Entry Calls ΓòÉΓòÉΓòÉ
1. An entry_call_statement (an entry call) can appear in various contexts. A
simple entry call is a stand-alone statement that represents an
unconditional call on an entry of a target task or a protected object.
Entry calls can also appear as part of select_statements, see 9.7.
Syntax
2.
entry_call_statement ::= entry_name [actual_parameter_part];
Name Resolution Rules
3. The entry_name given in an entry_call_statement shall resolve to denote
an entry. The rules for parameter associations are the same as for
subprogram calls, see 6.4, and 6.4.1.
Static Semantics
4. The entry_name of an entry_call_statement specifies (explicitly or
implicitly) the target object of the call, the entry or entry family, and
the entry index, if any, see 9.5.
Dynamic Semantics
5. Under certain circumstances (detailed below), an entry of a task or
protected object is checked to see whether it is open or closed:
a. An entry of a task is open if the task is blocked on an
accept_statement that corresponds to the entry, see 9.5.2, or on a
selective_accept, (see 9.7.1) with an open accept_alternative that
corresponds to the entry; otherwise it is closed.
b. An entry of a protected object is open if the condition of the
entry_barrier of the corresponding entry_body evaluates to True;
otherwise it is closed. If the evaluation of the condition
propagates an exception, the exception Program_Error is propagated
to all current callers of all entries of the protected object.
1. For the execution of an entry_call_statement, evaluation of the name and
of the parameter associations is as for a subprogram call, see 6.4. The
entry call is then issued: For a call on an entry of a protected object,
a new protected action is started on the object, see 9.5.1. The named
entry is checked to see if it is open; if open, the entry call is said to
be selected immediately, and the execution of the call proceeds as
follows:
a. For a call on an open entry of a task, the accepting task becomes
ready and continues the execution of the corresponding
accept_statement (see 9.5.2).
b. For a call on an open entry of a protected object, the corresponding
entry_body is executed, see 9.5.2, as part of the protected action.
1. If the accept_statement or entry_body completes other than by a requeue
(see 9.5.4) return is made to the caller (after servicing the entry
queues -- see below); any necessary assigning back of formal to actual
parameters occurs, as for a subprogram call, see 6.4.1, such assignments
take place outside of any protected action.
2. If the named entry is closed, the entry call is added to an entry queue
(as part of the protected action, for a call on a protected entry), and
the call remains queued until it is selected or cancelled; there is a
separate (logical) entry queue for each entry of a given task or
protected object (including each entry of an entry family).
3. When a queued call is selected, it is removed from its entry queue.
Selecting a queued call from a particular entry queue is called servicing
the entry queue. An entry with queued calls can be serviced under the
following circumstances:
a. When the associated task reaches a corresponding accept_statement,
or a selective_accept with a corresponding open accept_alternative;
b. If after performing, as part of a protected action on the associated
protected object, an operation on the object other than a call on a
protected function, the entry is checked and found to be open.
1. If there is at least one call on a queue corresponding to an open entry,
then one such call is selected according to the entry queuing policy in
effect (see below), and the corresponding accept_statement or entry_body
is executed as above for an entry call that is selected immediately.
2. The entry queuing policy controls selection among queued calls both for
task and protected entry queues. The default entry queuing policy is to
select calls on a given entry queue in order of arrival. If calls from
two or more queues are simultaneously eligible for selection, the default
entry queuing policy does not specify which queue is serviced first.
Other entry queuing policies can be specified by pragmas (see D.4).
3. For a protected object, the above servicing of entry queues continues
until there are no open entries with queued calls, at which point the
protected action completes.
4. For an entry call that is added to a queue, and that is not the
triggering_statement of an asynchronous_select, see 9.7.4, the calling
task is blocked until the call is cancelled, or the call is selected and
a corresponding accept_statement or entry_body completes without
requeuing. In addition, the calling task is blocked during a rendezvous.
5. An attempt can be made to cancel an entry call upon an abort (see 9.8)
and as part of certain forms of select_statement, see 9.7.2, 9.7.3, and
9.7.4. The cancellation does not take place until a point (if any) when
the call is on some entry queue, and not protected from cancellation as
part of a requeue, see 9.5.4, at such a point, the call is removed from
the entry queue and the call completes due to the cancellation. The
cancellation of a call on an entry of a protected object is a protected
action, and as such cannot take place while any other protected action is
occurring on the protected object. Like any protected action, it includes
servicing of the entry queues (in case some entry barrier depends on a
Count attribute).
6. A call on an entry of a task that has already completed its execution
raises the exception Tasking_Error at the point of the call; similarly,
this exception is raised at the point of the call if the called task
completes its execution or becomes abnormal before accepting the call or
completing the rendezvous, see 9.8. This applies equally to a simple
entry call and to an entry call as part of a select_statement.
Implementation Permissions
7. An implementation may perform the sequence of steps of a protected action
using any thread of control; it need not be that of the task that started
the protected action. If an entry_body completes without requeuing, then
the corresponding calling task may be made ready without waiting for the
entire protected action to complete.
8. When the entry of a protected object is checked to see whether it is
open, the implementation need not reevaluate the condition of the
corresponding entry_barrier if no variable or attribute referenced by the
condition (directly or indirectly) has been altered by the execution (or
cancellation) of a protected procedure or entry call on the object since
the condition was last evaluated.
9. An implementation may evaluate the conditions of all entry_barriers of a
given protected object any time any entry of the object is checked to see
if it is open.
10. When an attempt is made to cancel an entry call, the implementation need
not make the attempt using the thread of control of the task (or
interrupt) that initiated the cancellation; in particular, it may use the
thread of control of the caller itself to attempt the cancellation, even
if this might allow the entry call to be selected in the interim.
NOTES
11. (26) If an exception is raised during the execution of an entry_body, it
is propagated to the corresponding caller, see 11.4.
12. (27) For a call on a protected entry, the entry is checked to see if it
is open prior to queuing the call, and again thereafter if its Count
attribute, see 9.9, is referenced in some entry barrier.
13. (28) In addition to simple entry calls, the language permits timed,
conditional, and asynchronous entry calls, see 9.7.2, see 9.7.3, and
9.7.4.
14. (29) The condition of an entry_barrier is allowed to be evaluated by an
implementation more often than strictly necessary, even if the evaluation
might have side effects. On the other hand, an implementation need not
reevaluate the condition if nothing it references was updated by an
intervening protected action on the protected object, even if the
condition references some global variable that might have been updated by
an action performed from outside of a protected action.
Examples
15. Examples of entry calls:
16.
Agent.Shut_Down; -- see 9.1
Parser.Next_Lexeme(E); -- see 9.1
Pool(5).Read(Next_Char); -- see 9.1
Controller.Request(Low)(Some_Item); -- see 9.1
Flags(3).Seize; -- see 9.4
ΓòÉΓòÉΓòÉ 12.5.4. Requeue Statements ΓòÉΓòÉΓòÉ
1. A requeue_statement can be used to complete an accept_statement or
entry_body, while redirecting the corresponding entry call to a new (or
the same) entry queue. Such a requeue can be performed with or without
allowing an intermediate cancellation of the call, due to an abort or the
expiration of a delay.
Syntax
2.
requeue_statement ::= requeue entry_name [with abort];
Name Resolution Rules
3. The entry_name of a requeue_statement shall resolve to denote an entry
(the target entry) that either has no parameters, or that has a profile
that is type conformant, see 6.3.1, with the profile of the innermost
enclosing entry_body or accept_statement.
Legality Rules
4. A requeue_statement shall be within a callable construct that is either
an entry_body or an accept_statement, and this construct shall be the
innermost enclosing body or callable construct.
5. If the target entry has parameters, then its profile shall be subtype
conformant with the profile of the innermost enclosing callable
construct.
6. In a requeue_statement of an accept_statement of some task unit, either
the target object shall be a part of a formal parameter of the
accept_statement, or the accessibility level of the target object shall
not be equal to or statically deeper than any enclosing accept_statement
of the task unit. In a requeue_statement of an entry_body of some
protected unit, either the target object shall be a part of a formal
parameter of the entry_body, or the accessibility level of the target
object shall not be statically deeper than that of the entry_declaration.
Dynamic Semantics
7. The execution of a requeue_statement proceeds by first evaluating the
entry_name, including the prefix identifying the target task or protected
object and the expression identifying the entry within an entry family,
if any. The entry_body or accept_statement enclosing the
requeue_statement is then completed, finalized, and left, see 7.6.1.
8. For the execution of a requeue on an entry of a target task, after
leaving the enclosing callable construct, the named entry is checked to
see if it is open and the requeued call is either selected immediately or
queued, as for a normal entry call, see 9.5.3.
9. For the execution of a requeue on an entry of a target protected object,
after leaving the enclosing callable construct:
a. if the requeue is an internal requeue (that is, the requeue is back
on an entry of the same protected object -- see 9.5.), the call is
added to the queue of the named entry and the ongoing protected
action continues, see 9.5.1;
b. if the requeue is an external requeue (that is, the target protected
object is not implicitly the same as the current object -- see
9.5.), a protected action is started on the target object and
proceeds as for a normal entry call, see 9.5.3.
1. If the new entry named in the requeue_statement has formal parameters,
then during the execution of the accept_statement or entry_body
corresponding to the new entry, the formal parameters denote the same
objects as did the corresponding formal parameters of the callable
construct completed by the requeue. In any case, no parameters are
specified in a requeue_statement; any parameter passing is implicit.
2. If the requeue_statement includes the reserved words with abort (it is a
requeue-with-abort), then:
a. if the original entry call has been aborted, see 9.8, then the
requeue acts as an abort completion point for the call, and the call
is cancelled and no requeue is performed;
b. if the original entry call was timed (or conditional), then the
original expiration time is the expiration time for the requeued
call.
1. If the reserved words with abort do not appear, then the call remains
protected against cancellation while queued as the result of the
requeue_statement.
NOTES
2. (30) A requeue is permitted from a single entry to an entry of an entry
family, or vice-versa. The entry index, if any, plays no part in the
subtype conformance check between the profiles of the two entries; an
entry index is part of the entry_name for an entry of a family.
Examples
3. Examples of requeue statements:
4.
requeue Request(Medium) with abort;
-- requeue on a member of an entry family
-- of the current task, see 9.1
5.
requeue Flags(I).Seize;
-- requeue on an entry of an array
-- component, see 9.4
ΓòÉΓòÉΓòÉ 12.6. Delay Statements, Duration, and Time ΓòÉΓòÉΓòÉ
1. A delay_statement is used to block further execution until a specified
expiration time is reached. The expiration time can be specified either
as a particular point in time (in a delay_until_statement), or in seconds
from the current time (in a delay_relative_statement). The
language-defined package Calendar provides definitions for a type Time
and associated operations, including a function Clock that returns the
current time.
Syntax
2.
delay_statement ::= delay_until_statement | delay_relative_statement
3.
delay_until_statement ::= delay until delay_expression;
4.
delay_relative_statement ::= delay delay_expression;
Name Resolution Rules
5. The expected type for the delay_expression in a delay_relative_statement
is the predefined type Duration. The delay_expression in a
delay_until_statement is expected to be of any nonlimited type.
Legality Rules
6. There can be multiple time bases, each with a corresponding clock, and a
corresponding time type. The type of the delay_expression in a
delay_until_statement shall be a time type -- either the type Time
defined in the language-defined package Calendar (see below), or some
other implementation-defined time type, see D.8.
Static Semantics
7. There is a predefined fixed point type named Duration, declared in the
visible part of package Standard; a value of type Duration is used to
represent the length of an interval of time, expressed in seconds. The
type Duration is not specific to a particular time base, but can be used
with any time base.
8. A value of the type Time in package Calendar, or of some other
implementation-defined time type, represents a time as reported by a
corresponding clock.
9. The following language-defined library package exists:
10.
package Ada.Calendar is
type Time is private;
11.
subtype Year_Number is Integer range 1901 ┬╖┬╖ 2099;
subtype Month_Number is Integer range 1 ┬╖┬╖ 12;
subtype Day_Number is Integer range 1 ┬╖┬╖ 31;
subtype Day_Duration is Duration range 0.0 ┬╖┬╖ 86_400.0;
12.
function Clock return Time;
13.
function Year (Date : Time) return Year_Number;
function Month (Date : Time) return Month_Number;
function Day (Date : Time) return Day_Number;
function Seconds(Date : Time) return Day_Duration;
14.
procedure Split (Date : in Time;
Year : out Year_Number;
Month : out Month_Number;
Day : out Day_Number;
Seconds : out Day_Duration);
15.
function Time_Of(Year : Year_Number;
Month : Month_Number;
Day : Day_Number;
Seconds : Day_Duration := 0.0)
return Time;
16.
function "+" (Left : Time; Right : Duration) return Time;
function "+" (Left : Duration; Right : Time) return Time;
function "-" (Left : Time; Right : Duration) return Time;
function "-" (Left : Time; Right : Time) return Duration;
17.
function "<" (Left, Right : Time) return Boolean;
function "<="(Left, Right : Time) return Boolean;
function ">" (Left, Right : Time) return Boolean;
function ">="(Left, Right : Time) return Boolean;
18.
Time_Error : exception;
19.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Calendar;
Dynamic Semantics
20. For the execution of a delay_statement, the delay_expression is first
evaluated. For a delay_until_statement, the expiration time for the delay
is the value of the delay_expression, in the time base associated with
the type of the expression. For a delay_relative_statement, the
expiration time is defined as the current time, in the time base
associated with relative delays, plus the value of the delay_expression
converted to the type Duration, and then rounded up to the next clock
tick. The time base associated with relative delays is as defined in D.9:
``Delay Accuracy'', or is implementation defined.
21. The task executing a delay_statement is blocked until the expiration time
is reached, at which point it becomes ready again. If the expiration time
has already passed, the task is not blocked.
22. If an attempt is made to cancel the delay_statement (as part of an
asynchronous_select or abort -- see 9.7.4, and 9.8, the _statement is
cancelled if the expiration time has not yet passed, thereby completing
the delay_statement.
23. The time base associated with the type Time of package Calendar is
implementation defined. The function Clock of package Calendar returns a
value representing the current time for this time base. The
implementation-defined value of the named number System.Tick (see 13.7)
is an approximation of the length of the real-time interval during which
the value of Calendar.Clock remains constant.
24. The functions Year, Month, Day, and Seconds return the corresponding
values for a given value of the type Time, as appropriate to an
implementation-defined timezone; the procedure Split returns all four
corresponding values. Conversely, the function Time_Of combines a year
number, a month number, a day number, and a duration, into a value of
type Time. The operators "+" and "-" for addition and subtraction of
times and durations, and the relational operators for times, have the
conventional meaning.
25. If Time_Of is called with a seconds value of 86_400.0, the value returned
is equal to the value of Time_Of for the next day with a seconds value of
0.0. The value returned by the function Seconds or through the Seconds
parameter of the procedure Split is always less than 86_400.0.
26. The exception Time_Error is raised by the function Time_Of if the actual
parameters do not form a proper date. This exception is also raised by
the operators "+" and "-" if the result is not representable in the type
Time or Duration, as appropriate. This exception is also raised by the
function Year or the procedure Split if the year number of the given date
is outside of the range of the subtype Year_Number.
Implementation Requirements
27. The implementation of the type Duration shall allow representation of
time intervals (both positive and negative) up to at least 86400 seconds
(one day); Duration'Small shall not be greater than twenty milliseconds.
The implementation of the type Time shall allow representation of all
dates with year numbers in the range of Year_Number; it may allow
representation of other dates as well (both earlier and later).
Implementation Permissions
28. An implementation may define additional time types, see D.8.
29. An implementation may raise Time_Error if the value of a delay_expression
in a delay_until_statement of a select_statement represents a time more
than 90 days past the current time. The actual limit, if any, is
implementation-defined.
Implementation Advice
30. Whenever possible in an implementation, the value of Duration'Small
should be no greater than 100 microseconds.
31. The time base for delay_relative_statements should be monotonic; it need
not be the same time base as used for Calendar.Clock.
NOTES
32. (31) A delay_relative_statement with a negative value of the
delay_expression is equivalent to one with a zero value.
33. (32) A delay_statement may be executed by the environment task;
consequently delay_statements may be executed as part of the elaboration
of a library_item or the execution of the main subprogram. Such
statements delay the environment task, see 10.2.
34. (33) A delay_statement is an abort completion point and a potentially
blocking operation, even if the task is not actually blocked.
35. (34) There is no necessary relationship between System.Tick (the
resolution of the clock of package Calendar) and Duration'Small (the
small of type Duration).
36. (35) Additional requirements associated with delay_statements are given
in D.9: ``Delay Accuracy''.
Examples
37. Example of a relative delay statement:
38.
delay 3.0; -- delay 3.0 seconds
39. Example of a periodic task:
40.
declare
use Ada.Calendar;
Next_Time : Time := Clock + Period;
-- Period is a global constant of type Duration
begin
loop -- repeated every Period seconds
delay until Next_Time;
┬╖┬╖┬╖ -- perform some actions
Next_Time := Next_Time + Period;
end loop;
end;
ΓòÉΓòÉΓòÉ 12.7. Select Statements ΓòÉΓòÉΓòÉ
1. There are four forms of the select_statement. One form provides a
selective wait for one or more select_alternatives. Two provide timed and
conditional entry calls. The fourth provides asynchronous transfer of
control.
Syntax
2.
select_statement ::=
selective_accept
| timed_entry_call
| conditional_entry_call
| asynchronous_select
Examples
3. Example of a select statement:
4.
select
accept Driver_Awake_Signal;
or
delay 30.0*Seconds;
Stop_The_Train;
end select;
9.7.1 Selective Accept
9.7.2 Timed Entry Calls
9.7.3 Conditional Entry Calls
9.7.4 Asynchronous Transfer of Control
ΓòÉΓòÉΓòÉ 12.7.1. Selective Accept ΓòÉΓòÉΓòÉ
1. This form of the select_statement allows a combination of waiting for,
and selecting from, one or more alternatives. The selection may depend on
conditions associated with each alternative of the selective_accept.
Syntax
2.
selective_accept ::=
select
[guard]
select_alternative
{ or
[guard]
select_alternative }
[ else
sequence_of_statements ]
end select;
3.
guard ::= when condition =>
4.
select_alternative ::=
accept_alternative
| delay_alternative
| terminate_alternative
5.
accept_alternative ::=
accept_statement [sequence_of_statements]
6.
delay_alternative ::=
delay_statement [sequence_of_statements]
7.
terminate_alternative ::= terminate;
a. A selective_accept shall contain at least one accept_alternative. In
addition, it can contain:
1. a terminate_alternative (only one); or
2. one or more delay_alternatives; or
3. an else part (the reserved word else followed by a
sequence_of_statements).
a. These three possibilities are mutually exclusive.
Legality Rules
1. If a selective_accept contains more than one delay_alternative, then all
shall be delay_relative_statements, or all shall be
delay_until_statements for the same time type.
Dynamic Semantics
2. A select_alternative is said to be open if it is not immediately preceded
by a guard, or if the condition of its guard evaluates to True. It is
said to be closed otherwise.
3. For the execution of a selective_accept, any guard conditions are
evaluated; open alternatives are thus determined. For an open
delay_alternative, the delay_expression is also evaluated. Similarly, for
an open accept_alternative for an entry of a family, the entry_index is
also evaluated. These evaluations are performed in an arbitrary order,
except that a delay_expression or entry_index is not evaluated until
after evaluating the corresponding condition, if any. Selection and
execution of one open alternative, or of the else part, then completes
the execution of the selective_accept; the rules for this selection are
described below.
4. Open accept_alternatives are first considered. Selection of one such
alternative takes place immediately if the corresponding entry already
has queued calls. If several alternatives can thus be selected, one of
them is selected according to the entry queuing policy in effect (see
9.5.3 and D.4). When such an alternative is selected, the selected call
is removed from its entry queue and the handled_sequence_of_statements
(if any) of the corresponding accept_statement is executed; after the
rendezvous completes any subsequent sequence_of_statements of the
alternative is executed. If no selection is immediately possible (in the
above sense) and there is no else part, the task blocks until an open
alternative can be selected.
5. Selection of the other forms of alternative or of an else part is
performed as follows:
a. An open delay_alternative is selected when its expiration time is
reached if no accept_alternative or other delay_alternative can be
selected prior to the expiration time. If several delay_alternatives
have this same expiration time, one of them is selected according to
the queuing policy in effect, see D.4, the default queuing policy
chooses arbitrarily among the delay_alternatives whose expiration
time has passed.
b. The else part is selected and its sequence_of_statements is executed
if no accept_alternative can immediately be selected; in particular,
if all alternatives are closed.
c. An open terminate_alternative is selected if the conditions stated
at the end of clause (see 9.3) are satisfied.
1. The exception Program_Error is raised if all alternatives are closed and
there is no else part.
NOTES
2. (36) A selective_accept is allowed to have several open
delay_alternatives. A selective_accept is allowed to have several open
accept_alternatives for the same entry.
Examples
3. Example of a task body with a selective accept:
4.
task body Server is
Current_Work_Item : Work_Item;
begin
loop
select
accept Next_Work_Item(WI : in Work_Item) do
Current_Work_Item := WI;
end;
Process_Work_Item(Current_Work_Item);
or
accept Shut_Down;
exit; -- Premature shut down requested
or
terminate; -- Normal shutdown at end of scope
end select;
end loop;
end Server;
ΓòÉΓòÉΓòÉ 12.7.2. Timed Entry Calls ΓòÉΓòÉΓòÉ
1. A timed_entry_call issues an entry call that is cancelled if the call (or
a requeue-with-abort of the call) is not selected before the expiration
time is reached.
Syntax
2.
timed_entry_call ::=
select
entry_call_alternative
or
delay_alternative
end select;
3.
entry_call_alternative ::=
entry_call_statement [sequence_of_statements]
Dynamic Semantics
4. For the execution of a timed_entry_call, the entry_name and the actual
parameters are evaluated, as for a simple entry call, see 9.5.3. The
expiration time, see 9.6 for the call is determined by evaluating the
delay_expression of the delay_alternative; the entry call is then issued.
5. If the call is queued (including due to a requeue-with-abort), and not
selected before the expiration time is reached, an attempt to cancel the
call is made. If the call completes due to the cancellation, the optional
sequence_of_statements of the delay_alternative is executed; if the entry
call completes normally, the optional sequence_of_statements of the
entry_call_alternative is executed.
Examples
6. Example of a timed entry call:
7.
select
Controller.Request(Medium)(Some_Item);
or
delay 45.0;
-- controller too busy, try something else
end select;
ΓòÉΓòÉΓòÉ 12.7.3. Conditional Entry Calls ΓòÉΓòÉΓòÉ
1. A conditional_entry_call issues an entry call that is then cancelled if
it is not selected immediately (or if a requeue-with-abort of the call is
not selected immediately).
Syntax
2.
conditional_entry_call ::=
select
entry_call_alternative
else
sequence_of_statements
end select;
Dynamic Semantics
3. The execution of a conditional_entry_call is defined to be equivalent to
the execution of a timed_entry_call with a delay_alternative specifying
an immediate expiration time and the same sequence_of_statements as given
after the reserved word else.
NOTES
4. (37) A conditional_entry_call may briefly increase the Count attribute of
the entry, even if the conditional call is not selected.
Examples
5. Example of a conditional entry call:
6.
procedure Spin(R : in Resource) is
begin
loop
select
R.Seize;
return;
else
null; -- busy waiting
end select;
end loop;
end;
ΓòÉΓòÉΓòÉ 12.7.4. Asynchronous Transfer of Control ΓòÉΓòÉΓòÉ
1. An asynchronous select_statement provides asynchronous transfer of
control upon completion of an entry call or the expiration of a delay.
Syntax
2.
asynchronous_select ::=
select
triggering_alternative
then abort
abortable_part
end select;
3.
triggering_alternative ::=
triggering_statement [sequence_of_statements]
4.
triggering_statement ::= entry_call_statement | delay_statement
5.
abortable_part ::= sequence_of_statements
Dynamic Semantics
6. For the execution of an asynchronous_select whose triggering_statement is
an entry_call_statement, the entry_name and actual parameters are
evaluated as for a simple entry call, see 9.5.3, and the entry call is
issued. If the entry call is queued (or requeued-with-abort), then the
abortable_part is executed. If the entry call is selected immediately,
and never requeued-with-abort, then the abortable_part is never started.
7. For the execution of an asynchronous_select whose triggering_statement is
a delay_statement, the delay_expression is evaluated and the expiration
time is determined, as for a normal delay_statement. If the expiration
time has not already passed, the abortable_part is executed.
8. If the abortable_part completes and is left prior to completion of the
triggering_statement, an attempt to cancel the triggering_statement is
made. If the attempt to cancel succeeds, see 9.5.3, and 9.6, the
asynchronous_select is complete.
9. If the triggering_statement completes other than due to cancellation, the
abortable_part is aborted (if started but not yet completed -- see 9.8).
If the triggering_statement completes normally, the optional
sequence_of_statements of the triggering_alternative is executed after
the abortable_part is left.
Examples
10. Example of a main command loop for a command interpreter:
11.
loop
select
Terminal.Wait_For_Interrupt;
Put_Line("Interrupted");
then abort
-- This will be abandoned upon terminal interrupt
Put_Line("-> ");
Get_Line(Command, Last);
Process_Command(Command(1┬╖┬╖Last));
end select;
end loop;
12. Example of a time-limited calculation:
13.
select
delay 5.0;
Put_Line("Calculation does not converge");
then abort
-- This calculation should finish in 5.0 seconds;
-- if not, it is assumed to diverge.
Horribly_Complicated_Recursive_Function(X, Y);
end select;
ΓòÉΓòÉΓòÉ 12.8. Abort of a Task - Abort of a Sequence of Statements ΓòÉΓòÉΓòÉ
1. An abort_statement causes one or more tasks to become abnormal, thus
preventing any further interaction with such tasks. The completion of the
triggering_statement of an asynchronous_select causes a
sequence_of_statements to be aborted.
Syntax
2.
abort_statement ::= abort task_name {, task_name};
Name Resolution Rules
3. Each task_name is expected to be of any task type; they need not all be
of the same task type.
Dynamic Semantics
4. For the execution of an abort_statement, the given task_names are
evaluated in an arbitrary order. Each named task is then aborted, which
consists of making the task abnormal and aborting the execution of the
corresponding task_body, unless it is already completed.
5. When the execution of a construct is aborted (including that of a
task_body or of a sequence_of_statements), the execution of every
construct included within the aborted execution is also aborted, except
for executions included within the execution of an abort-deferred
operation; the execution of an abort-deferred operation continues to
completion without being affected by the abort; the following are the
abort-deferred operations:
a. a protected action;
b. waiting for an entry call to complete (after having initiated the
attempt to cancel it -- see below);
c. waiting for the termination of dependent tasks;
d. the execution of an Initialize procedure as the last step of the
default initialization of a controlled object;
e. the execution of a Finalize procedure as part of the finalization of
a controlled object;
f. an assignment operation to an object with a controlled part.
1. The last three of these are discussed further in 7.6.
2. When a master is aborted, all tasks that depend on that master are
aborted.
3. The order in which tasks become abnormal as the result of an
abort_statement or the abort of a sequence_of_statements is not specified
by the language.
4. If the execution of an entry call is aborted, an immediate attempt is
made to cancel the entry call, see 9.5.3. If the execution of a construct
is aborted at a time when the execution is blocked, other than for an
entry call, at a point that is outside the execution of an abort-deferred
operation, then the execution of the construct completes immediately. For
an abort due to an abort_statement, these immediate effects occur before
the execution of the abort_statement completes. Other than for these
immediate cases, the execution of a construct that is aborted does not
necessarily complete before the abort_statement completes. However, the
execution of the aborted construct completes no later than its next abort
completion point (if any) that occurs outside of an abort-deferred
operation; the following are abort completion points for an execution:
a. the point where the execution initiates the activation of another
task;
b. the end of the activation of a task;
c. the start or end of the execution of an entry call,
accept_statement, delay_statement, or abort_statement;
d. the start of the execution of a select_statement, or of the
sequence_of_statements of an exception_handler.
Bounded (Run-Time) Errors
1. An attempt to execute an asynchronous_select as part of the execution of
an abort-deferred operation is a bounded error. Similarly, an attempt to
create a task that depends on a master that is included entirely within
the execution of an abort-deferred operation is a bounded error. In both
cases, Program_Error is raised if the error is detected by the
implementation; otherwise the operations proceed as they would outside an
abort-deferred operation, except that an abort of the abortable_part or
the created task might or might not have an effect.
Erroneous Execution
2. If an assignment operation completes prematurely due to an abort, the
assignment is said to be disrupted; the target of the assignment or its
parts can become abnormal, and certain subsequent uses of the object can
be erroneous, as explained in 13.9.1.
NOTES
3. (38) An abort_statement should be used only in situations requiring
unconditional termination.
4. (39) A task is allowed to abort any task it can name, including itself.
5. (40) Additional requirements associated with abort are given in D.6:
``Preemptive Abort''.
ΓòÉΓòÉΓòÉ 12.9. Task and Entry Attributes ΓòÉΓòÉΓòÉ
Dynamic Semantics
1. For a prefix T that is of a task type (after any implicit dereference),
the following attributes are defined:
2. T'Callable
Yields the value True when the task denoted by T is callable,
and False otherwise; a task is callable unless it is
completed or abnormal. The value of this attribute is of the
predefined type Boolean.
3. T'Terminated
Yields the value True if the task denoted by T is terminated,
and False otherwise. The value of this attribute is of the
predefined type Boolean.
4. For a prefix E that denotes an entry of a task or protected unit, the
following attribute is defined. This attribute is only allowed within the
body of the task or protected unit, but excluding, in the case of an
entry of a task unit, within any program unit that is, itself, inner to
the body of the task unit.
5. E'Count
Yields the number of calls presently queued on the entry E of
the current instance of the unit. The value of this
attribute is of the type universal_integer.
NOTES
6. (41) For the Count attribute, the entry can be either a single entry or
an entry of a family. The name of the entry or entry family can be either
a direct_name or an expanded name.
7. (42) Within task units, algorithms interrogating the attribute E'Count
should take precautions to allow for the increase of the value of this
attribute for incoming entry calls, and its decrease, for example with
timed_entry_calls. Also, a conditional_entry_call may briefly increase
this value, even if the conditional call is not accepted.
8. (43) Within protected units, algorithms interrogating the attribute
E'Count in the entry_barrier for the entry E should take precautions to
allow for the evaluation of the condition of the barrier both before and
after queuing a given caller.
ΓòÉΓòÉΓòÉ 12.10. Shared Variables ΓòÉΓòÉΓòÉ
Static Semantics
1. If two different objects, including nonoverlapping parts of the same
object, are independently addressable, they can be manipulated
concurrently by two different tasks without synchronization. Normally,
any two nonoverlapping objects are independently addressable. However, if
packing, record layout, or Component_Size is specified for a given
composite object, then it is implementation defined whether or not two
nonoverlapping parts of that composite object are independently
addressable.
Dynamic Semantics
2. Separate tasks normally proceed independently and concurrently with one
another. However, task interactions can be used to synchronize the
actions of two or more tasks to allow, for example, meaningful
communication by the direct updating and reading of variables shared
between the tasks. The actions of two different tasks are synchronized in
this sense when an action of one task signals an action of the other
task; an action A1 is defined to signal an action A2 under the following
circumstances:
a. If A1 and A2 are part of the execution of the same task, and the
language rules require A1 to be performed before A2;
b. If A1 is the action of an activator that initiates the activation of
a task, and A2 is part of the execution of the task that is
activated;
c. If A1 is part of the activation of a task, and A2 is the action of
waiting for completion of the activation;
d. If A1 is part of the execution of a task, and A2 is the action of
waiting for the termination of the task;
e. If A1 is the action of issuing an entry call, and A2 is part of the
corresponding execution of the appropriate entry_body or
accept_statement.
f. If A1 is part of the execution of an accept_statement or entry_body,
and A2 is the action of returning from the corresponding entry call;
g. If A1 is part of the execution of a protected procedure body or
entry_body for a given protected object, and A2 is part of a later
execution of an entry_body for the same protected object;
h. If A1 signals some action that in turn signals A2.
Erroneous Execution
1. Given an action of assigning to an object, and an action of reading or
updating a part of the same object (or of a neighboring object if the two
are not independently addressable), then the execution of the actions is
erroneous unless the actions are sequential. Two actions are sequential
if one of the following is true:
a. One action signals the other;
b. Both actions occur as part of the execution of the same task;
c. Both actions occur as part of protected actions on the same
protected object, and at most one of the actions is part of a call
on a protected function of the protected object.
1. A pragma Atomic or Atomic_Components may also be used to ensure that
certain reads and updates are sequential -- see C.6.
ΓòÉΓòÉΓòÉ 12.11. Example of Tasking and Synchronization ΓòÉΓòÉΓòÉ
Examples
1. The following example defines a buffer protected object to smooth
variations between the speed of output of a producing task and the speed
of input of some consuming task. For instance, the producing task might
have the following structure:
2.
task Producer;
3.
task body Producer is
Char : Character;
begin
loop
┬╖┬╖┬╖ -- produce the next character Char
Buffer.Write(Char);
exit when Char = ASCII.EOT;
end loop;
end Producer;
4. and the consuming task might have the following structure:
5.
task Consumer;
6.
task body Consumer is
Char : Character;
begin
loop
Buffer.Read(Char);
exit when Char = ASCII.EOT;
┬╖┬╖┬╖ -- consume the character Char
end loop;
end Consumer;
7. The buffer object contains an internal pool of characters managed in a
round-robin fashion. The pool has two indices, an In_Index denoting the
space for the next input character and an Out_Index denoting the space
for the next output character.
8.
protected Buffer is
entry Read (C : out Character);
entry Write(C : in Character);
private
Pool : String(1 ┬╖┬╖ 100);
Count : Natural := 0;
In_Index, Out_Index : Positive := 1;
end Buffer;
9.
protected body Buffer is
entry Write(C : in Character)
when Count < Pool'Length is
begin
Pool(In_Index) := C;
In_Index := (In_Index mod Pool'Length) + 1;
Count := Count + 1;
end Write;
10.
entry Read(C : out Character)
when Count > 0 is
begin
C := Pool(Out_Index);
Out_Index := (Out_Index mod Pool'Length) + 1;
Count := Count - 1;
end Read;
end Buffer;
ΓòÉΓòÉΓòÉ 13. Program Structure and Compilation Issues ΓòÉΓòÉΓòÉ
1. The overall structure of programs and the facilities for separate
compilation are described in this section. A program is a set of
partitions, each of which may execute in a separate address space,
possibly on a separate computer.
2. As explained below, a partition is constructed from library units.
Syntactically, the declaration of a library unit is a library_item, as is
the body of a library unit. An implementation may support a concept of a
program library (or simply, a ``library''), which contains library_items
and their subunits. Library units may be organized into a hierarchy of
children, grandchildren, and so on.
3. This section has two clauses: (see 10.1: ``Separate Compilation'')
discusses compile-time issues related to separate compilation. (see 10.2:
``Program Execution'') discusses issues related to what is traditionally
known as ``link time'' and ``run time'' -- building and executing
partitions.
10.1 Separate Compilation
10.2 Program Execution --- The Detailed Node Listing
---
10.1 Separate Compilation
10.1.1 Compilation Units - Library Units
10.1.2 Context Clauses - With Clauses
10.1.3 Subunits of Compilation Units
10.1.4 The Compilation Process
10.1.5 Pragmas and Program Units
10.1.6 Environment-Level Visibility Rules
10.2 Program Execution
10.2.1 Elaboration Control
ΓòÉΓòÉΓòÉ 13.1. Separate Compilation ΓòÉΓòÉΓòÉ
1. A program unit is either a package, a task unit, a protected unit, a
protected entry, a generic unit, or an explicitly declared subprogram
other than an enumeration literal. Certain kinds of program units can be
separately compiled. Alternatively, they can appear physically nested
within other program units.
2. The text of a program can be submitted to the compiler in one or more
compilations. Each compilation is a succession of compilation_units. A
compilation_unit contains either the declaration, the body, or a renaming
of a program unit. The representation for a compilation is
implementation-defined.
3. A library unit is a separately compiled program unit, and is always a
package, subprogram, or generic unit. Library units may have other
(logically nested) library units as children, and may have other program
units physically nested within them. A root library unit, together with
its children and grandchildren and so on, form a subsystem.
Implementation Permissions
4. An implementation may impose implementation-defined restrictions on
compilations that contain multiple compilation_units.
10.1.1 Compilation Units - Library Units
10.1.2 Context Clauses - With Clauses
10.1.3 Subunits of Compilation Units
10.1.4 The Compilation Process
10.1.5 Pragmas and Program Units
10.1.6 Environment-Level Visibility Rules
ΓòÉΓòÉΓòÉ 13.1.1. Compilation Units - Library Units ΓòÉΓòÉΓòÉ
1. A library_item is a compilation unit that is the declaration, body, or
renaming of a library unit. Each library unit (except Standard) has a
parent unit, which is a library package or generic library package. A
library unit is a child of its parent unit. The root library units are
the children of the predefined library package Standard.
Syntax
2.
compilation ::= {compilation_unit}
3.
compilation_unit ::=
context_clause library_item
| context_clause subunit
4.
library_item ::= [private] library_unit_declaration
| library_unit_body
| [private] library_unit_renaming_declaration
5.
library_unit_declaration ::=
subprogram_declaration | package_declaration
| generic_declaration | generic_instantiation
6.
library_unit_renaming_declaration ::=
package_renaming_declaration
| generic_renaming_declaration
| subprogram_renaming_declaration
7.
library_unit_body ::= subprogram_body | package_body
8.
parent_unit_name ::= name
9. A library unit is a program unit that is declared by a library_item. When
a program unit is a library unit, the prefix ``library'' is used to refer
to it (or ``generic library'' if generic), as well as to its declaration
and body, as in ``library procedure'', ``library package_body'', or
``generic library package''. The term compilation unit is used to refer
to a compilation_unit. When the meaning is clear from context, the term
is also used to refer to the library_item of a compilation_unit or to the
proper_body of a subunit (that is, the compilation_unit without the
context_clause and the separate (parent_unit_name)).
10. The parent declaration of a library_item (and of the library unit) is the
declaration denoted by the parent_unit_name, if any, of the
defining_program_unit_name of the library_item. If there is no
parent_unit_name, the parent declaration is the declaration of Standard,
the library_item is a root library_item, and the library unit (renaming)
is a root library unit (renaming). The declaration and body of Standard
itself have no parent declaration. The parent unit of a library_item or
library unit is the library unit declared by its parent declaration.
11. The children of a library unit occur immediately within the declarative
region of the declaration of the library unit. The ancestors of a library
unit are itself, its parent, its parent's parent, and so on. (Standard is
an ancestor of every library unit.) The descendant relation is the
inverse of the ancestor relation.
12. A library_unit_declaration or a library_unit_renaming_declaration is
private if the declaration is immediately preceded by the reserved word
private; it is otherwise public. A library unit is private or public
according to its declaration. The public descendants of a library unit
are the library unit itself, and the public descendants of its public
children. Its other descendants are private descendants.
Legality Rules
13. The parent unit of a library_item shall be a library package or generic
library package.
14. If a defining_program_unit_name of a given declaration or body has a
parent_unit_name, then the given declaration or body shall be a
library_item. The body of a program unit shall be a library_item if and
only if the declaration of the program unit is a library_item. In a
library_unit_renaming_declaration, the (old) name shall denote a
library_item.
15. A parent_unit_name (which can be used within a defining_program_unit_name
of a library_item and in the separate clause of a subunit), and each of
its prefixes, shall not denote a renaming_declaration. On the other hand,
a name that denotes a library_unit_renaming_declaration is allowed in a
with_clause and other places where the name of a library unit is allowed.
16. If a library package is an instance of a generic package, then every
child of the library package shall either be itself an instance or be a
renaming of a library unit.
17. A child of a generic library package shall either be itself a generic
unit or be a renaming of some other child of the same generic unit. The
renaming of a child of a generic package shall occur only within the
declarative region of the generic package.
18. A child of a parent generic package shall be instantiated or renamed only
within the declarative region of the parent generic.
19. For each declaration or renaming of a generic unit as a child of some
parent generic package, there is a corresponding declaration nested
immediately within each instance of the parent. This declaration is
visible only within the scope of a with_clause that mentions the child
generic unit.
20. A library subprogram shall not override a primitive subprogram.
21. The defining name of a function that is a compilation unit shall not be
an operator_symbol.
Static Semantics
22. A subprogram_renaming_declaration that is a
library_unit_renaming_declaration is a renaming-as-declaration, not a
renaming-as-body.
23. There are two kinds of dependences among compilation units:
a. The semantic dependences (see below) are the ones needed to check
the compile-time rules across compilation unit boundaries; a
compilation unit depends semantically on the other compilation units
needed to determine its legality. The visibility rules are based on
the semantic dependences.
b. The elaboration dependences, see 10.2, determine the order of
elaboration of library_items.
1. A library_item depends semantically upon its parent declaration. A
subunit depends semantically upon its parent body. A library_unit_body
depends semantically upon the corresponding library_unit_declaration, if
any. A compilation unit depends semantically upon each library_item
mentioned in a with_clause of the compilation unit. In addition, if a
given compilation unit contains an attribute_reference of a type defined
in another compilation unit, then the given compilation unit depends
semantically upon the other compilation unit. The semantic dependence
relationship is transitive.
NOTES
2. (1) A simple program may consist of a single compilation unit. A
compilation need not have any compilation units; for example, its text
can consist of pragmas.
3. (2) The designator of a library function cannot be an operator_symbol,
but a nonlibrary renaming_declaration is allowed to rename a library
function as an operator. Within a partition, two library subprograms are
required to have distinct names and hence cannot overload each other.
However, renaming_declarations are allowed to define overloaded names for
such subprograms, and a locally declared subprogram is allowed to
overload a library subprogram. The expanded name Standard.L can be used
to denote a root library unit L (unless the declaration of Standard is
hidden) since root library unit declarations occur immediately within the
declarative region of package Standard.
Examples
4. Examples of library units:
5.
package Rational_Numbers.IO is
-- public child of Rational_Numbers, see 7.1
procedure Put(R : in Rational);
procedure Get(R : out Rational);
end Rational_Numbers.IO;
6.
private procedure Rational_Numbers.Reduce(R : in out Rational);
-- private child of Rational_Numbers
7.
with Rational_Numbers.Reduce; -- refer to a private child
package body Rational_Numbers is
┬╖┬╖┬╖
end Rational_Numbers;
8.
with Rational_Numbers.IO; use Rational_Numbers;
with Ada.Text_io; -- see A.10
procedure Main is -- a root library procedure
R : Rational;
begin
R := 5/3; -- construct a rational number, see 7.1
Ada.Text_IO.Put("The answer is: ");
IO.Put(R);
Ada.Text_IO.New_Line;
end Main;
9.
with Rational_Numbers.IO;
package Rational_IO renames Rational_Numbers.IO;
-- a library unit renaming declaration
10. Each of the above library_items can be submitted to the compiler
separately.
ΓòÉΓòÉΓòÉ 13.1.2. Context Clauses - With Clauses ΓòÉΓòÉΓòÉ
1. A context_clause is used to specify the library_items whose names are
needed within a compilation unit.
Syntax
2.
context_clause ::= {context_item}
3.
context_item ::= with_clause | use_clause
4.
with_clause ::= with library_unit_name {, library_unit_name};
Name Resolution Rules
5. The scope of a with_clause that appears on a library_unit_declaration or
library_unit_renaming_declaration consists of the entire declarative
region of the declaration, which includes all children and subunits. The
scope of a with_clause that appears on a body consists of the body, which
includes all subunits.
6. A library_item is mentioned in a with_clause if it is denoted by a
library_unit_name or a prefix in the with_clause.
7. Outside its own declarative region, the declaration or renaming of a
library unit can be visible only within the scope of a with_clause that
mentions it. The visibility of the declaration or renaming of a library
unit otherwise follows from its placement in the environment.
Legality Rules
8. If a with_clause of a given compilation_unit mentions a private child of
some library unit, then the given compilation_unit shall be either the
declaration of a private descendant of that library unit or the body or
subunit of a (public or private) descendant of that library unit.
NOTES
9. (3) A library_item mentioned in a with_clause of a compilation unit is
visible within the compilation unit and hence acts just like an ordinary
declaration. Thus, within a compilation unit that mentions its
declaration, the name of a library package can be given in use_clauses
and can be used to form expanded names, a library subprogram can be
called, and instances of a generic library unit can be declared. If a
child of a parent generic package is mentioned in a with_clause, then the
corresponding declaration nested within each visible instance is visible
within the compilation unit.
ΓòÉΓòÉΓòÉ 13.1.3. Subunits of Compilation Units ΓòÉΓòÉΓòÉ
1. Subunits are like child units, with these (important) differences:
subunits support the separate compilation of bodies only (not
declarations); the parent contains a body_stub to indicate the existence
and place of each of its subunits; declarations appearing in the parent's
body can be visible within the subunits.
Syntax
2.
body_stub ::=
subprogram_body_stub
| package_body_stub
| task_body_stub
| protected_body_stub
3.
subprogram_body_stub ::= subprogram_specification is separate;
4.
package_body_stub ::= package body defining_identifier is separate;
5.
task_body_stub ::= task body defining_identifier is separate;
6.
protected_body_stub ::=
protected body defining_identifier is separate;
7.
subunit ::= separate (parent_unit_name) proper_body
Legality Rules
8. The parent body of a subunit is the body of the program unit denoted by
its parent_unit_name. The term subunit is used to refer to a subunit and
also to the proper_body of a subunit.
9. The parent body of a subunit shall be present in the current environment,
and shall contain a corresponding body_stub with the same
defining_identifier as the subunit.
10. A package_body_stub shall be the completion of a package_declaration or
generic_package_declaration; a task_body_stub shall be the completion of
a task_declaration; a protected_body_stub shall be the completion of a
protected_declaration.
11. In contrast, a subprogram_body_stub need not be the completion of a
previous declaration, in which case the _stub declares the subprogram. If
the _stub is a completion, it shall be the completion of a
subprogram_declaration or generic_subprogram_declaration. The profile of
a subprogram_body_stub that completes a declaration shall conform fully
to that of the declaration.
12. A subunit that corresponds to a body_stub shall be of the same kind
(package_, subprogram_, task_, or protected_) as the body_stub. The
profile of a subprogram_body subunit shall be fully conformant to that of
the corresponding body_stub.
13. A body_stub shall appear immediately within the declarative_part of a
compilation unit body. This rule does not apply within an instance of a
generic unit.
14. The defining_identifiers of all body_stubs that appear immediately within
a particular declarative_part shall be distinct.
Post-Compilation Rules
15. For each body_stub, there shall be a subunit containing the corresponding
proper_body.
NOTES
16. (4) The rules in 10.1.4: ``The Compilation Process'', say that a
body_stub is equivalent to the corresponding proper_body. This implies:
a. Visibility within a subunit is the visibility that would be obtained
at the place of the corresponding body_stub (within the parent body)
if the context_clause of the subunit were appended to that of the
parent body.
b. The effect of the elaboration of a body_stub is to elaborate the
subunit.
Examples
1. The package Parent is first written without subunits:
2.
package Parent is
procedure Inner;
end Parent;
3.
with Ada.Text_IO;
package body Parent is
Variable : String := "Hello, there.";
procedure Inner is
begin
Ada.Text_IO.Put_Line(Variable);
end Inner;
end Parent;
4. The body of procedure Inner may be turned into a subunit by rewriting the
package body as follows (with the declaration of Parent remaining the
same):
5.
package body Parent is
Variable : String := "Hello, there.";
procedure Inner is separate;
end Parent;
6.
with Ada.Text_IO;
separate(Parent)
procedure Inner is
begin
Ada.Text_IO.Put_Line(Variable);
end Inner;
ΓòÉΓòÉΓòÉ 13.1.4. The Compilation Process ΓòÉΓòÉΓòÉ
1. Each compilation unit submitted to the compiler is compiled in the
context of an environment declarative_part (or simply, an environment),
which is a conceptual declarative_part that forms the outermost
declarative region of the context of any compilation. At run time, an
environment forms the declarative_part of the body of the environment
task of a partition, see 10.2: ``Program Execution''.
2. The declarative_items of the environment are library_items appearing in
an order such that there are no forward semantic dependences. Each
included subunit occurs in place of the corresponding stub. The
visibility rules apply as if the environment were the outermost
declarative region, except that with_clauses are needed to make
declarations of library units visible, see 10.1.2.
3. The mechanisms for creating an environment and for adding and replacing
compilation units within an environment are implementation defined.
Name Resolution Rules
4. If a library_unit_body that is a subprogram_body is submitted to the
compiler, it is interpreted only as a completion if a
library_unit_declaration for a subprogram or a generic subprogram with
the same defining_program_unit_name already exists in the environment
(even if the profile of the body is not type conformant with that of the
declaration); otherwise the subprogram_body is interpreted as both the
declaration and body of a library subprogram.
Legality Rules
5. When a compilation unit is compiled, all compilation units upon which it
depends semantically shall already exist in the environment; the set of
these compilation units shall be consistent in the sense that the new
compilation unit shall not semantically depend (directly or indirectly)
on two different versions of the same compilation unit, nor on an earlier
version of itself.
Implementation Permissions
6. The implementation may require that a compilation unit be legal before
inserting it into the environment.
7. When a compilation unit that declares or renames a library unit is added
to the environment, the implementation may remove from the environment
any preexisting library_item with the same defining_program_unit_name.
When a compilation unit that is a subunit or the body of a library unit
is added to the environment, the implementation may remove from the
environment any preexisting version of the same compilation unit. When a
given compilation unit is removed from the environment, the
implementation may also remove any compilation unit that depends
semantically upon the given one. If the given compilation unit contains
the body of a subprogram to which a pragma Inline applies, the
implementation may also remove any compilation unit containing a call to
that subprogram.
NOTES
8. (5) The rules of the language are enforced across compilation and
compilation unit boundaries, just as they are enforced within a single
compilation unit.
9. (6) An implementation may support a concept of a library, which contains
library_items. If multiple libraries are supported, the implementation
has to define how a single environment is constructed when a compilation
unit is submitted to the compiler. Naming conflicts between different
libraries might be resolved by treating each library as the root of a
hierarchy of child library units.
10. (7) A compilation unit containing an instantiation of a separately
compiled generic unit does not semantically depend on the body of the
generic unit. Therefore, replacing the generic body in the environment
does not result in the removal of the compilation unit containing the
instantiation.
ΓòÉΓòÉΓòÉ 13.1.5. Pragmas and Program Units ΓòÉΓòÉΓòÉ
1. This subclause discusses pragmas related to program units, library units,
and compilations.
Name Resolution Rules
2. Certain pragmas are defined to be program unit pragmas. A name given as
the argument of a program unit pragma shall resolve to denote the
declarations or renamings of one or more program units that occur
immediately within the declarative region or compilation in which the
pragma immediately occurs, or it shall resolve to denote the declaration
of the immediately enclosing program unit (if any); the pragma applies to
the denoted program unit(s). If there are no names given as arguments,
the pragma applies to the immediately enclosing program unit.
Legality Rules
3. A program unit pragma shall appear in one of these places:
a. At the place of a compilation_unit, in which case the pragma shall
immediately follow in the same compilation (except for other
pragmas) a library_unit_declaration that is a
subprogram_declaration, generic_subprogram_declaration, or
generic_instantiation, and the pragma shall have an argument that is
a name denoting that declaration.
b. Immediately within the declaration of a program unit and before any
nested declaration, in which case the argument, if any, shall be a
direct_name that denotes the immediately enclosing program unit
declaration.
c. At the place of a declaration other than the first, of a
declarative_part or program unit declaration, in which case the
pragma shall have an argument, which shall be a direct_name that
denotes one or more of the following (and nothing else): a
subprogram_declaration, a generic_subprogram_declaration, or a
generic_instantiation, of the same declarative_part or program unit
declaration.
1. Certain program unit pragmas are defined to be library unit pragmas. The
name, if any, in a library unit pragma shall denote the declaration of a
library unit.
Post-Compilation Rules
2. Certain pragmas are defined to be configuration pragmas; they shall
appear before the first compilation_unit of a compilation. They are
generally used to select a partition-wide or system-wide option. The
pragma applies to all compilation_units appearing in the compilation,
unless there are none, in which case it applies to all future
compilation_units compiled into the same environment.
Implementation Permissions
3. An implementation may place restrictions on configuration pragmas, so
long as it allows them when the environment contains no library_items
other than those of the predefined environment.
ΓòÉΓòÉΓòÉ 13.1.6. Environment-Level Visibility Rules ΓòÉΓòÉΓòÉ
1. The normal visibility rules do not apply within a parent_unit_name or a
context_clause, nor within a pragma that appears at the place of a
compilation unit. The special visibility rules for those contexts are
given here.
Static Semantics
2. Within the parent_unit_name at the beginning of a library_item, and
within a with_clause, the only declarations that are visible are those
that are library_items of the environment, and the only declarations that
are directly visible are those that are root library_items of the
environment. Notwithstanding the rules of 4.1.3, an expanded name in a
with_clause may consist of a prefix that denotes a generic package and a
selector_name that denotes a child of that generic package (The child is
necessarily a generic unit, see See 10.1.1).
3. Within a use_clause or pragma that is within a context_clause, each
library_item mentioned in a previous with_clause of the same
context_clause is visible, and each root library_item so mentioned is
directly visible. In addition, within such a use_clause, if a given
declaration is visible or directly visible, each declaration that occurs
immediately within the given declaration's visible part is also visible.
No other declarations are visible or directly visible.
4. Within the parent_unit_name of a subunit, library_items are visible as
they are in the parent_unit_name of a library_item; in addition, the
declaration corresponding to each body_stub in the environment is also
visible.
5. Within a pragma that appears at the place of a compilation unit, the
immediately preceding library_item and each of its ancestors is visible.
The ancestor root library_item is directly visible.
ΓòÉΓòÉΓòÉ 13.2. Program Execution ΓòÉΓòÉΓòÉ
1. An Ada program consists of a set of partitions, which can execute in
parallel with one another, possibly in a separate address space, and
possibly on a separate computer.
Post-Compilation Rules
2. A partition is a program or part of a program that can be invoked from
outside the Ada implementation. For example, on many systems, a partition
might be an executable file generated by the system linker. The user can
explicitly assign library units to a partition. The assignment is done in
an implementation-defined manner. The compilation units included in a
partition are those of the explicitly assigned library units, as well as
other compilation units needed by those library units. The compilation
units needed by a given compilation unit are determined as follows
(unless specified otherwise via an implementation-defined pragma, or by
some other implementation-defined means):
a. A compilation unit needs itself;
b. If a compilation unit is needed, then so are any compilation units
upon which it depends semantically;
c. If a library_unit_declaration is needed, then so is any
corresponding library_unit_body;
d. If a compilation unit with stubs is needed, then so are any
corresponding subunits.
1. The user can optionally designate (in an implementation-defined manner)
one subprogram as the main subprogram for the partition. A main
subprogram, if specified, shall be a subprogram.
2. Each partition has an anonymous environment task, which is an implicit
outermost task whose execution elaborates the library_items of the
environment declarative_part, and then calls the main subprogram, if
there is one. A partition's execution is that of its tasks.
3. The order of elaboration of library units is determined primarily by the
elaboration dependences. There is an elaboration dependence of a given
library_item upon another if the given library_item or any of its
subunits depends semantically on the other library_item. In addition, if
a given library_item or any of its subunits has a pragma Elaborate or
Elaborate_All that mentions another library unit, then there is an
elaboration dependence of the given library_item upon the body of the
other library unit, and, for Elaborate_All only, upon each library_item
needed by the declaration of the other library unit.
4. The environment task for a partition has the following structure:
5.
task Environment_Task;
6.
task body Environment_Task is
┬╖┬╖┬╖ (1) -- The environment declarative_part
-- (that is, the sequence of library_items) goes here.
begin
┬╖┬╖┬╖ (2) -- Call the main subprogram, if there is one.
end Environment_Task;
7. The environment declarative_part at (1) is a sequence of
declarative_items consisting of copies of the library_items included in
the partition. The order of elaboration of library_items is the order in
which they appear in the environment declarative_part:
a. The order of all included library_items is such that there are no
forward elaboration dependences.
b. Any included library_unit_declaration to which a pragma
Elaborate_Body applies is immediately followed by its
library_unit_body, if included.
c. All library_items declared pure occur before any that are not
declared pure.
d. All preelaborated library_items occur before any that are not
preelaborated.
1. There shall be a total order of the library_items that obeys the above
rules. The order is otherwise implementation defined.
2. The full expanded names of the library units and subunits included in a
given partition shall be distinct.
3. The sequence_of_statements of the environment task (see (2) above)
consists of either:
1. A call to the main subprogram, if the partition has one. If the
main subprogram has parameters, they are passed; where the
actuals come from is implementation defined. What happens to
the result of a main function is also implementation defined.
a. or:
1. A null_statement, if there is no main subprogram.
1. The mechanisms for building and running partitions are implementation
defined. These might be combined into one operation, as, for example, in
dynamic linking, or ``load-and-go'' systems.
Dynamic Semantics
2. The execution of a program consists of the execution of a set of
partitions. Further details are implementation defined. The execution of
a partition starts with the execution of its environment task, ends when
the environment task terminates, and includes the executions of all tasks
of the partition. The execution of the (implicit) task_body of the
environment task acts as a master for all other tasks created as part of
the execution of the partition. When the environment task completes
(normally or abnormally), it waits for the termination of all such tasks,
and then finalizes any remaining objects of the partition.
Bounded (Run-Time) Errors
3. Once the environment task has awaited the termination of all other tasks
of the partition, any further attempt to create a task (during
finalization) is a bounded error, and may result in the raising of
Program_Error either upon creation or activation of the task. If such a
task is activated, it is not specified whether the task is awaited prior
to termination of the environment task.
Implementation Requirements
4. The implementation shall ensure that all compilation units included in a
partition are consistent with one another, and are legal according to the
rules of the language.
Implementation Permissions
5. The kind of partition described in this clause is known as an active
partition. An implementation is allowed to support other kinds of
partitions, with implementation-defined semantics.
6. An implementation may restrict the kinds of subprograms it supports as
main subprograms. However, an implementation is required to support all
main subprograms that are public parameterless library procedures.
7. If the environment task completes abnormally, the implementation may
abort any dependent tasks.
NOTES
8. (8) An implementation may provide inter-partition communication
mechanism(s) via special packages and pragmas. Standard pragmas for
distribution and methods for specifying inter-partition communication are
defined in E: ``Distributed Systems''. If no such mechanisms are
provided, then each partition is isolated from all others, and behaves as
a program in and of itself.
9. (9) Partitions are not required to run in separate address spaces. For
example, an implementation might support dynamic linking via the
partition concept.
10. (10) An order of elaboration of library_items that is consistent with the
partial ordering defined above does not always ensure that each
library_unit_body is elaborated before any other compilation unit whose
elaboration necessitates that the library_unit_body be already elaborated
(In particular, there is no requirement that the body of a library unit
be elaborated as soon as possible after the library_unit_declaration is
elaborated, unless the pragmas in subclause, see 10.2.1, are used).
11. (11) A partition (active or otherwise) need not have a main subprogram.
In such a case, all the work done by the partition would be done by
elaboration of various library_items, and by tasks created by that
elaboration. Passive partitions, which cannot have main subprograms, are
defined in E: ``Distributed Systems''.
10.2.1 Elaboration Control
ΓòÉΓòÉΓòÉ 13.2.1. Elaboration Control ΓòÉΓòÉΓòÉ
1. This subclause defines pragmas that help control the elaboration order of
library_items.
Syntax
2. The form of a pragma Preelaborate is as follows:
3.
pragma Preelaborate[(library_unit_name)];
a. A pragma Preelaborate is a library unit pragma.
Legality Rules
1. An elaborable construct is preelaborable unless its elaboration performs
any of the following actions:
a. The execution of a statement other than a null_statement.
b. A call to a subprogram other than a static function.
c. The evaluation of a primary that is a name of an object, unless the
name is a static expression, or statically denotes a discriminant of
an enclosing type.
d. The creation of a default-initialized object (including a component)
of a descendant of a private type, private extension, controlled
type, task type, or protected type with entry_declarations;
similarly the evaluation of an extension_aggregate with an ancestor
subtype_mark denoting a subtype of such a type.
1. A generic body is preelaborable only if elaboration of a corresponding
instance body would not perform any such actions, presuming that the
actual for each formal private type (or extension) is a private type (or
extension), and the actual for each formal subprogram is a user-defined
subprogram.
2. If a pragma Preelaborate (or pragma Pure -- see below) applies to a
library unit, then it is preelaborated. If a library unit is
preelaborated, then its declaration, if any, and body, if any, are
elaborated prior to all non-preelaborated library_items of the partition.
All compilation units of a preelaborated library unit shall be
preelaborable. In addition to the places where Legality Rules normally
apply, see 12.3, this rule applies also in the private part of an
instance of a generic unit. In addition, all compilation units of a
preelaborated library unit shall depend semantically only on compilation
units of other preelaborated library units.
Implementation Advice
3. In an implementation, a type declared in a preelaborated package should
have the same representation in every elaboration of a given version of
the package, whether the elaborations occur in distinct executions of the
same program, or in executions of distinct programs or partitions that
include the given version.
Syntax
4. The form of a pragma Pure is as follows:
5.
pragma Pure[(library_unit_name)];
a. A pragma Pure is a library unit pragma.
Legality Rules
1. A pure library_item is a preelaborable library_item that does not contain
the declaration of any variable or named access type, except within a
subprogram, generic subprogram, task unit, or protected unit.
2. A pragma Pure is used to declare that a library unit is pure. If a pragma
Pure applies to a library unit, then its compilation units shall be pure,
and they shall depend semantically only on compilation units of other
library units that are declared pure.
Implementation Permissions
3. If a library unit is declared pure, then the implementation is permitted
to omit a call on a library-level subprogram of the library unit if the
results are not needed after the call. Similarly, it may omit such a call
and simply reuse the results produced by an earlier call on the same
subprogram, provided that none of the parameters are of a limited type,
and the addresses and values of all by-reference actual parameters, and
the values of all by-copy-in actual parameters, are the same as they were
at the earlier call. This permission applies even if the subprogram
produces other side effects when called.
Syntax
4. The form of a pragma Elaborate, Elaborate_All, or Elaborate_Body is as
follows:
5.
pragma Elaborate(library_unit_name{, library_unit_name});
6.
pragma Elaborate_All(library_unit_name{, library_unit_name});
7.
pragma Elaborate_Body[(library_unit_name)];
a. A pragma Elaborate or Elaborate_All is only allowed within a
context_clause.
b. A pragma Elaborate_Body is a library unit pragma.
Legality Rules
1. If a pragma Elaborate_Body applies to a declaration, then the declaration
requires a completion (a body).
Static Semantics
2. A pragma Elaborate specifies that the body of the named library unit is
elaborated before the current library_item. A pragma Elaborate_All
specifies that each library_item that is needed by the named library unit
declaration is elaborated before the current library_item. A pragma
Elaborate_Body specifies that the body of the library unit is elaborated
immediately after its declaration.
NOTES
3. (12) A preelaborated library unit is allowed to have non-preelaborable
children.
4. (13) A library unit that is declared pure is allowed to have impure
children.
ΓòÉΓòÉΓòÉ 14. Exceptions ΓòÉΓòÉΓòÉ
1. This section defines the facilities for dealing with errors or other
exceptional situations that arise during program execution. An exception
represents a kind of exceptional situation; an occurrence of such a
situation (at run time) is called an exception occurrence. To raise an
exception is to abandon normal program execution so as to draw attention
to the fact that the corresponding situation has arisen. Performing some
actions in response to the arising of an exception is called handling the
exception.
2. An exception_declaration declares a name for an exception. An exception
is raised initially either by a raise_statement or by the failure of a
language-defined check. When an exception arises, control can be
transferred to a user-provided exception_handler at the end of a
handled_sequence_of_statements, or it can be propagated to a dynamically
enclosing execution.
11.1 Exception Declarations
11.2 Exception Handlers
11.3 Raise Statements
11.4 Exception Handling
11.5 Suppressing Checks
11.6 Exceptions and Optimization --- The Detailed
Node Listing ---
11.1 Exception Declarations
11.2 Exception Handlers
11.3 Raise Statements
11.4 Exception Handling
11.4.1 The Package Exceptions
11.4.2 Example of Exception Handling
11.5 Suppressing Checks
11.6 Exceptions and Optimization
ΓòÉΓòÉΓòÉ 14.1. Exception Declarations ΓòÉΓòÉΓòÉ
1. An exception_declaration declares a name for an exception.
Syntax
2. exception_declaration ::= defining_identifier_list : exception;
Static Semantics
3. Each single exception_declaration declares a name for a different
exception. If a generic unit includes an exception_declaration, the
exception_declarations implicitly generated by different instantiations
of the generic unit refer to distinct exceptions (but all have the same
defining_identifier). The particular exception denoted by an exception
name is determined at compilation time and is the same regardless of how
many times the exception_declaration is elaborated.
4. The predefined exceptions are the ones declared in the declaration of
package Standard: Constraint_Error, Program_Error, Storage_Error, and
Tasking_Error; one of them is raised when a language-defined check fails.
Dynamic Semantics
5. The elaboration of an exception_declaration has no effect.
6. The execution of any construct raises Storage_Error if there is
insufficient storage for that execution. The amount of storage needed for
the execution of constructs is unspecified.
Examples
7. Examples of user-defined exception declarations:
8.
Singular : exception;
Error : exception;
Overflow, Underflow : exception;
ΓòÉΓòÉΓòÉ 14.2. Exception Handlers ΓòÉΓòÉΓòÉ
1. The response to one or more exceptions is specified by an
exception_handler.
Syntax
2.
handled_sequence_of_statements ::=
sequence_of_statements
[exception
exception_handler
{exception_handler}]
3.
exception_handler ::=
when [choice_parameter_specification:]
exception_choice {| exception_choice} =>
sequence_of_statements
4.
choice_parameter_specification ::= defining_identifier
5.
exception_choice ::= exception_name | others
Legality Rules
6. A choice with an exception_name covers the named exception. A choice with
others covers all exceptions not named by previous choices of the same
handled_sequence_of_statements. Two choices in different
exception_handlers of the same handled_sequence_of_statements shall not
cover the same exception.
7. A choice with others is allowed only for the last handler of a
handled_sequence_of_statements and as the only choice of that handler.
8. An exception_name of a choice shall not denote an exception declared in a
generic formal package.
Static Semantics
9. A choice_parameter_specification declares a choice parameter, which is a
constant object of type Exception_Occurrence, see 11.4.1. During the
handling of an exception occurrence, the choice parameter, if any, of the
handler represents the exception occurrence that is being handled.
Dynamic Semantics
10. The execution of a handled_sequence_of_statements consists of the
execution of the sequence_of_statements. The optional handlers are used
to handle any exceptions that are propagated by the
sequence_of_statements.
Examples
11. Example of an exception handler:
12.
begin
Open(File, In_File, "input.txt"); -- see A.8.2
exception
when E : Name_Error =>
Put("Cannot open input file : ");
Put_Line(Exception_Message(E)); -- see 11.4.1
raise;
end;
ΓòÉΓòÉΓòÉ 14.3. Raise Statements ΓòÉΓòÉΓòÉ
1. A raise_statement raises an exception.
Syntax
2.
raise_statement ::= raise [exception_name];
Legality Rules
3. The name, if any, in a raise_statement shall denote an exception. A
raise_statement with no exception_name (that is, a re-raise statement)
shall be within a handler, but not within a body enclosed by that
handler.
Dynamic Semantics
4. To raise an exception is to raise a new occurrence of that exception, as
explained in 11.4. For the execution of a raise_statement with an
exception_name, the named exception is raised. For the execution of a
re-raise statement, the exception occurrence that caused transfer of
control to the innermost enclosing handler is raised again.
Examples
5. Examples of raise statements:
6.
raise Ada.IO_Exceptions.Name_Error; -- see A.13
7.
raise;
-- re-raise the current exception
ΓòÉΓòÉΓòÉ 14.4. Exception Handling ΓòÉΓòÉΓòÉ
1. When an exception occurrence is raised, normal program execution is
abandoned and control is transferred to an applicable exception_handler,
if any. To handle an exception occurrence is to respond to the
exceptional event. To propagate an exception occurrence is to raise it
again in another context; that is, to fail to respond to the exceptional
event in the present context.
Dynamic Semantics
2. Within a given task, if the execution of construct a is defined by this
International Standard to consist (in part) of the execution of construct
b, then while b is executing, the execution of a is said to dynamically
enclose the execution of b. The innermost dynamically enclosing execution
of a given execution is the dynamically enclosing execution that started
most recently.
3. When an exception occurrence is raised by the execution of a given
construct, the rest of the execution of that construct is abandoned; that
is, any portions of the execution that have not yet taken place are not
performed. The construct is first completed, and then left, as explained
in 7.6.1. Then:
a. If the construct is a task_body, the exception does not propagate
further;
b. If the construct is the sequence_of_statements of a
handled_sequence_of_statements that has a handler with a choice
covering the exception, the occurrence is handled by that handler;
c. Otherwise, the occurrence is propagated to the innermost dynamically
enclosing execution, which means that the occurrence is raised again
in that context.
1. When an occurrence is handled by a given handler, the
choice_parameter_specification, if any, is first elaborated, which
creates the choice parameter and initializes it to the occurrence. Then,
the sequence_of_statements of the handler is executed; this execution
replaces the abandoned portion of the execution of the
sequence_of_statements.
NOTES
2. (1) Note that exceptions raised in a declarative_part of a body are not
handled by the handlers of the handled_sequence_of_statements of that
body.
11.4.1 The Package Exceptions
11.4.2 Example of Exception Handling
ΓòÉΓòÉΓòÉ 14.4.1. The Package Exceptions ΓòÉΓòÉΓòÉ
Static Semantics
1. The following language-defined library package exists:
2.
package Ada.Exceptions is
type Exception_Id is private;
Null_Id : constant Exception_Id;
function Exception_Name(Id : Exception_Id) return String;
3.
type Exception_Occurrence is limited private;
type Exception_Occurrence_Access is
access all Exception_Occurrence;
Null_Occurrence : constant Exception_Occurrence;
4.
procedure Raise_Exception
(E : in Exception_Id;
Message : in String := "");
function Exception_Message(X : Exception_Occurrence)
return String;
procedure Reraise_Occurrence(X : in Exception_Occurrence);
5.
function Exception_Identity(X : Exception_Occurrence)
return Exception_Id;
function Exception_Name(X : Exception_Occurrence)
return String;
-- Same as Exception_Name(Exception_Identity(X)).
function Exception_Information(X : Exception_Occurrence)
return String;
6.
procedure Save_Occurrence(Target : out Exception_Occurrence;
Source : in Exception_Occurrence);
function Save_Occurrence(Source : Exception_Occurrence)
return Exception_Occurrence_Access;
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Exceptions;
7. Each distinct exception is represented by a distinct value of type
Exception_Id. Null_Id does not represent any exception, and is the
default initial value of type Exception_Id. Each occurrence of an
exception is represented by a value of type Exception_Occurrence.
Null_Occurrence does not represent any exception occurrence, and is the
default initial value of type Exception_Occurrence.
8. For a prefix E that denotes an exception, the following attribute is
defined:
9. E'Identity
E'Identity returns the unique identity of the exception. The
type of this attribute is Exception_Id.
10. Raise_Exception raises a new occurrence of the identified exception. In
this case, Exception_Message returns the Message parameter of
Raise_Exception. For a raise_statement with an exception_name,
Exception_Message returns implementation-defined information about the
exception occurrence. Reraise_Occurrence reraises the specified exception
occurrence.
11. Exception_Identity returns the identity of the exception of the
occurrence.
12. The Exception_Name functions return the full expanded name of the
exception, in upper case, starting with a root library unit. For an
exception declared immediately within package Standard, the
defining_identifier is returned. The result is implementation defined if
the exception is declared within an unnamed block_statement.
13. Exception_Information returns implementation-defined information about
the exception occurrence.
14. Raise_Exception and Reraise_Occurrence have no effect in the case of
Null_Id or Null_Occurrence. Exception_Message, Exception_Identity,
Exception_Name, and Exception_Information raise Constraint_Error for a
Null_Id or Null_Occurrence.
15. The Save_Occurrence procedure copies the Source to the Target. The
Save_Occurrence function uses an allocator of type
Exception_Occurrence_Access to create a new object, copies the Source to
this new object, and returns an access value designating this new object;
the result may be deallocated using an instance of
Unchecked_Deallocation.
Implementation Requirements
16. The implementation of the Write attribute, see 13.13.2, of
Exception_Occurrence shall support writing a representation of an
exception occurrence to a stream; the implementation of the Read
attribute of Exception_Occurrence shall support reconstructing an
exception occurrence from a stream (including one written in a different
partition).
Implementation Permissions
17. An implementation of Exception_Name in a space-constrained environment
may return the defining_identifier instead of the full expanded name.
18. The string returned by Exception_Message may be truncated (to no less
than 200 characters) by the Save_Occurrence procedure (not the function),
the Reraise_Occurrence procedure, and the re-raise statement.
Implementation Advice
19. Exception_Message (by default) and Exception_Information should produce
information useful for debugging. Exception_Message should be short
(about one line), whereas Exception_Information can be long.
Exception_Message should not include the Exception_Name.
Exception_Information should include both the Exception_Name and the
Exception_Message.
ΓòÉΓòÉΓòÉ 14.4.2. Example of Exception Handling ΓòÉΓòÉΓòÉ
Examples
1. Exception handling may be used to separate the detection of an error from
the response to that error:
2.
with Ada.Exceptions;
use Ada;
package File_System is
type File_Handle is limited private;
3.
File_Not_Found : exception;
procedure Open(F : in out File_Handle; Name : String);
-- raises File_Not_Found if named file does not exist
4.
End_Of_File : exception;
procedure Read(F : in out File_Handle; Data : out Data_Type);
-- raises End_Of_File if the file is not open
5.
┬╖┬╖┬╖
end File_System;
6.
package body File_System is
procedure Open(F : in out File_Handle; Name : String) is
begin
if File_Exists(Name) then
┬╖┬╖┬╖
else
Exceptions.Raise_Exception
(File_Not_Found'Identity,
"File not found: " & Name & ".");
end if;
end Open;
7.
procedure Read(F : in out File_Handle; Data : out Data_Type) is
begin
if F.Current_Position <= F.Last_Position then
┬╖┬╖┬╖
else
raise End_Of_File;
end if;
end Read;
8.
┬╖┬╖┬╖
9.
end File_System;
10.
with Ada.Text_IO;
with Ada.Exceptions;
with File_System; use File_System;
use Ada;
procedure Main is
begin
┬╖┬╖┬╖ -- call operations in File_System
exception
when End_Of_File =>
Close(Some_File);
when Not_Found_Error : File_Not_Found =>
Text_IO.Put_Line
(Exceptions.Exception_Message(Not_Found_Error));
when The_Error : others =>
Text_IO.Put_Line("Unknown error:");
if Verbosity_Desired then
Text_IO.Put_Line(Exceptions.Exception_Information
(The_Error));
else
Text_IO.Put_Line(Exceptions.Exception_Name
(The_Error));
Text_IO.Put_Line(Exceptions.Exception_Message
(The_Error));
end if;
raise;
end Main;
11. In the above example, the File_System package contains information about
detecting certain exceptional situations, but it does not specify how to
handle those situations. Procedure Main specifies how to handle them;
other clients of File_System might have different handlers, even though
the exceptional situations arise from the same basic causes.
ΓòÉΓòÉΓòÉ 14.5. Suppressing Checks ΓòÉΓòÉΓòÉ
1. A pragma Suppress gives permission to an implementation to omit certain
language-defined checks.
2. A language-defined check (or simply, a ``check'') is one of the
situations defined by this International Standard that requires a check
to be made at run time to determine whether some condition is true. A
check fails when the condition being checked is false, causing an
exception to be raised.
Syntax
3. The form of a pragma Suppress is as follows:
4.
pragma Suppress(identifier [, [On =>] name]);
a. A pragma Suppress is allowed only immediately within a
declarative_part, immediately within a package_specification, or as
a configuration pragma.
Legality Rules
1. The identifier shall be the name of a check. The name (if present) shall
statically denote some entity.
2. For a pragma Suppress that is immediately within a package_specification
and includes a name, the name shall denote an entity (or several
overloaded subprograms) declared immediately within the
package_specification.
Static Semantics
3. A pragma Suppress gives permission to an implementation to omit the named
check from the place of the pragma to the end of the innermost enclosing
declarative region, or, if the pragma is given in a package_specification
and includes a name, to the end of the scope of the named entity. If the
pragma includes a name, the permission applies only to checks performed
on the named entity, or, for a subtype, on objects and values of its
type. Otherwise, the permission applies to all entities. If permission
has been given to suppress a given check, the check is said to be
suppressed.
4. The following are the language-defined checks:
a. The following checks correspond to situations in which the exception
Constraint_Error is raised upon failure.
1. Access_Check
When evaluating a dereference (explicit or
implicit), check that the value of the name is
not null. When passing an actual parameter to a
formal access parameter, check that the value of
the actual parameter is not null.
2. Discriminant_Check
Check that the discriminants of a composite value
have the values imposed by a discriminant
constraint. Also, when accessing a record
component, check that it exists for the current
discriminant values.
3. Division_Check
Check that the second operand is not zero for the
operations /, rem and mod.
4. Index_Check
Check that the bounds of an array value are equal
to the corresponding bounds of an index
constraint. Also, when accessing a component of
an array object, check for each dimension that
the given index value belongs to the range
defined by the bounds of the array object. Also,
when accessing a slice of an array object, check
that the given discrete range is compatible with
the range defined by the bounds of the array
object.
5. Length_Check
Check that two arrays have matching components,
in the case of array subtype conversions, and
logical operators for arrays of boolean
components.
6. Overflow_Check
Check that a scalar value is within the base
range of its type, in cases where the
implementation chooses to raise an exception
instead of returning the correct mathematical
result.
7. Range_Check
Check that a scalar value satisfies a range
constraint. Also, for the elaboration of a
subtype_indication, check that the constraint (if
present) is compatible with the subtype denoted
by the subtype_mark. Also, for an aggregate,
check that an index or discriminant value belongs
to the corresponding subtype. Also, check that
when the result of an operation yields an array,
the value of each component belongs to the
component subtype.
8. Tag_Check
Check that operand tags in a dispatching call are
all equal. Check for the correct tag on tagged
type conversions, for an assignment_statement,
and when returning a tagged limited object from a
function.
a. The following checks correspond to situations in which the exception
Program_Error is raised upon failure.
1. Elaboration_Check
When a subprogram or protected entry is called, a
task activation is accomplished, or a generic
instantiation is elaborated, check that the body
of the corresponding unit has already been
elaborated.
2. Accessibility_Check
Check the accessibility level of an entity or
view.
a. The following check corresponds to situations in which the exception
Storage_Error is raised upon failure.
1. Storage_Check
Check that evaluation of an allocator does not
require more space than is available for a
storage pool. Check that the space available for
a task or subprogram has not been exceeded.
a. The following check corresponds to all situations in which any
predefined exception is raised.
1. All_Checks
Represents the union of all checks; suppressing
All_Checks suppresses all checks.
Erroneous Execution
1. If a given check has been suppressed, and the corresponding error
situation occurs, the execution of the program is erroneous.
Implementation Permissions
2. An implementation is allowed to place restrictions on Suppress pragmas.
An implementation is allowed to add additional check names, with
implementation-defined semantics. When Overflow_Check has been
suppressed, an implementation may also suppress an unspecified subset of
the Range_Checks.
Implementation Advice
3. The implementation should minimize the code executed for checks that have
been suppressed.
NOTES
4. (2) There is no guarantee that a suppressed check is actually removed;
hence a pragma Suppress should be used only for efficiency reasons.
Examples
5. Examples of suppressing checks:
6.
pragma Suppress(Range_Check);
pragma Suppress(Index_Check, On => Table);
ΓòÉΓòÉΓòÉ 14.6. Exceptions and Optimization ΓòÉΓòÉΓòÉ
1. This clause gives permission to the implementation to perform certain
``optimizations'' that do not necessarily preserve the canonical
semantics.
Dynamic Semantics
2. The rest of this International Standard (outside this clause) defines the
canonical semantics of the language. The canonical semantics of a given
(legal) program determines a set of possible external effects that can
result from the execution of the program with given inputs.
3. As explained in 1.1.3: ``Conformity of an Implementation With the
Standard'', the external effect of a program is defined in terms of its
interactions with its external environment. Hence, the implementation can
perform any internal actions whatsoever, in any order or in parallel, so
long as the external effect of the execution of the program is one that
is allowed by the canonical semantics, or by the rules of this clause.
Implementation Permissions
4. The following additional permissions are granted to the implementation:
a. An implementation need not always raise an exception when a
language-defined check fails. Instead, the operation that failed the
check can simply yield an undefined result. The exception need be
raised by the implementation only if, in the absence of raising it,
the value of this undefined result would have some effect on the
external interactions of the program. In determining this, the
implementation shall not presume that an undefined result has a
value that belongs to its subtype, nor even to the base range of its
type, if scalar. Having removed the raise of the exception, the
canonical semantics will in general allow the implementation to omit
the code for the check, and some or all of the operation itself.
b. If an exception is raised due to the failure of a language-defined
check, then upon reaching the corresponding exception_handler (or
the termination of the task, if none), the external interactions
that have occurred need reflect only that the exception was raised
somewhere within the execution of the sequence_of_statements with
the handler (or the task_body), possibly earlier (or later if the
interactions are independent of the result of the checked operation)
than that defined by the canonical semantics, but not within the
execution of some abort-deferred operation or independent subprogram
that does not dynamically enclose the execution of the construct
whose check failed. An independent subprogram is one that is defined
outside the library unit containing the construct whose check
failed, and has no Inline pragma applied to it. Any assignment that
occurred outside of such abort-deferred operations or independent
subprograms can be disrupted by the raising of the exception,
causing the object or its parts to become abnormal, and certain
subsequent uses of the object to be erroneous, as explained in
13.9.1.
NOTES
1. (3) The permissions granted by this clause can have an effect on the
semantics of a program only if the program fails a language-defined
check.
ΓòÉΓòÉΓòÉ 15. Generic Units ΓòÉΓòÉΓòÉ
1. A generic unit is a program unit that is either a generic subprogram or a
generic package. A generic unit is a template, which can be
parameterized, and from which corresponding (nongeneric) subprograms or
packages can be obtained. The resulting program units are said to be
instances of the original generic unit.
2. A generic unit is declared by a generic_declaration. This form of
declaration has a generic_formal_part declaring any generic formal
parameters. An instance of a generic unit is obtained as the result of a
generic_instantiation with appropriate generic actual parameters for the
generic formal parameters. An instance of a generic subprogram is a
subprogram. An instance of a generic package is a package.
3. Generic units are templates. As templates they do not have the properties
that are specific to their nongeneric counterparts. For example, a
generic subprogram can be instantiated but it cannot be called. In
contrast, an instance of a generic subprogram is a (nongeneric)
subprogram; hence, this instance can be called but it cannot be used to
produce further instances.
12.1 Generic Declarations
12.2 Generic Bodies
12.3 Generic Instantiation
12.4 Formal Objects
12.5 Formal Types
12.6 Formal Subprograms
12.7 Formal Packages
12.8 Example of a Generic Package --- The Detailed
Node Listing ---
12.1 Generic Declarations
12.2 Generic Bodies
12.3 Generic Instantiation
12.4 Formal Objects
12.5 Formal Types
12.5.1 Formal Private and Derived Types
12.5.2 Formal Scalar Types
12.5.3 Formal Array Types
12.5.4 Formal Access Types
12.6 Formal Subprograms
12.7 Formal Packages
12.8 Example of a Generic Package
ΓòÉΓòÉΓòÉ 15.1. Generic Declarations ΓòÉΓòÉΓòÉ
1. A generic_declaration declares a generic unit, which is either a generic
subprogram or a generic package. A generic_declaration includes a
generic_formal_part declaring any generic formal parameters. A generic
formal parameter can be an object; alternatively (unlike a parameter of a
subprogram), it can be a type, a subprogram, or a package.
Syntax
2.
generic_declaration ::=
generic_subprogram_declaration | generic_package_declaration
3.
generic_subprogram_declaration ::=
generic_formal_part subprogram_specification;
4.
generic_package_declaration ::=
generic_formal_part package_specification;
5.
generic_formal_part ::=
generic {generic_formal_parameter_declaration | use_clause}
6.
generic_formal_parameter_declaration ::=
formal_object_declaration
| formal_type_declaration
| formal_subprogram_declaration
| formal_package_declaration
a. The only form of subtype_indication allowed within a
generic_formal_part is a subtype_mark (that is, the
subtype_indication shall not include an explicit constraint). The
defining name of a generic subprogram shall be an identifier (not an
operator_symbol).
Static Semantics
1. A generic_declaration declares a generic unit -- a generic package,
generic procedure or generic function, as appropriate.
2. An entity is a generic formal entity if it is declared by a
generic_formal_parameter_declaration. ``Generic formal,'' or simply
``formal,'' is used as a prefix in referring to objects, subtypes (and
types), functions, procedures and packages, that are generic formal
entities, as well as to their respective declarations. Examples:
``generic formal procedure'' or a ``formal integer type declaration.''
Dynamic Semantics
3. The elaboration of a generic_declaration has no effect.
NOTES
4. (1) Outside a generic unit a name that denotes the generic_declaration
denotes the generic unit. In contrast, within the declarative region of
the generic unit, a name that denotes the generic_declaration denotes the
current instance.
5. (2) Within a generic subprogram_body, the name of this program unit acts
as the name of a subprogram. Hence this name can be overloaded, and it
can appear in a recursive call of the current instance. For the same
reason, this name cannot appear after the reserved word new in a
(recursive) generic_instantiation.
6. (3) A default_expression or default_name appearing in a
generic_formal_part is not evaluated during elaboration of the
generic_formal_part; instead, it is evaluated when used. (The usual
visibility rules apply to any name used in a default: the denoted
declaration therefore has to be visible at the place of the expression.)
Examples
7. Examples of generic formal parts:
8.
generic -- parameterless
9.
generic
Size : Natural; -- formal object
10.
generic
Length : Integer := 200;
-- formal object with a default expression
11.
Area : Integer := Length*Length;
-- formal object with a default expression
12.
generic
type Item is private; -- formal type
type Index is (<>); -- formal type
type Row is array(Index range <>) of Item; -- formal type
with function "<"(X, Y : Item) return Boolean;
-- formal subprogram
13. Examples of generic declarations declaring generic subprograms Exchange
and Squaring:
14.
generic
type Elem is private;
procedure Exchange(U, V : in out Elem);
15.
generic
type Item is private;
with function "*"(U, V : Item) return Item is <>;
function Squaring(X : Item) return Item;
16. Example of a generic declaration declaring a generic package:
17.
generic
type Item is private;
type Vector is array (Positive range <>) of Item;
with function Sum(X, Y : Item) return Item;
package On_Vectors is
function Sum (A, B : Vector) return Vector;
function Sigma(A : Vector) return Item;
Length_Error : exception;
end On_Vectors;
ΓòÉΓòÉΓòÉ 15.2. Generic Bodies ΓòÉΓòÉΓòÉ
1. The body of a generic unit (a generic body) is a template for the
instance bodies. The syntax of a generic body is identical to that of a
nongeneric body.
Dynamic Semantics
2. The elaboration of a generic body has no other effect than to establish
that the generic unit can from then on be instantiated without failing
the Elaboration_Check. If the generic body is a child of a generic
package, then its elaboration establishes that each corresponding
declaration nested in an instance of the parent, see 10.1.1, can from
then on be instantiated without failing the Elaboration_Check.
NOTES
3. (4) The syntax of generic subprograms implies that a generic subprogram
body is always the completion of a declaration.
Examples
4. Example of a generic procedure body:
5.
procedure Exchange(U, V : in out Elem) is -- see 12.1
T : Elem; -- the generic formal type
begin
T := U;
U := V;
V := T;
end Exchange;
6. Example of a generic function body:
7.
function Squaring(X : Item) return Item is -- see 12.1
begin
return X*X; -- the formal operator "*"
end Squaring;
8. Example of a generic package body:
9.
package body On_Vectors is -- see 12.1
10.
function Sum(A, B : Vector) return Vector is
Result : Vector(A'Range); -- the formal type Vector
Bias : constant Integer := B'First - A'First;
begin
if A'Length /= B'Length then
raise Length_Error;
end if;
11.
for N in A'Range loop
Result(N) := Sum(A(N), B(N + Bias));
-- the formal function Sum
end loop;
return Result;
end Sum;
12.
function Sigma(A : Vector) return Item is
Total : Item := A(A'First); -- the formal type Item
begin
for N in A'First + 1 ┬╖┬╖ A'Last loop
Total := Sum(Total, A(N)); -- the formal function Sum
end loop;
return Total;
end Sigma;
end On_Vectors;
ΓòÉΓòÉΓòÉ 15.3. Generic Instantiation ΓòÉΓòÉΓòÉ
1. An instance of a generic unit is declared by a generic_instantiation.
Syntax
2.
generic_instantiation ::=
package defining_program_unit_name is
new generic_package_name [generic_actual_part];
| procedure defining_program_unit_name is
new generic_procedure_name [generic_actual_part];
| function defining_designator is
new generic_function_name [generic_actual_part];
3.
generic_actual_part ::=
(generic_association {, generic_association})
4.
generic_association ::=
[generic_formal_parameter_selector_name =>]
explicit_generic_actual_parameter
5.
explicit_generic_actual_parameter ::= expression | variable_name
| subprogram_name | entry_name | subtype_mark
| package_instance_name
a. A generic_association is named or positional according to whether or
not the generic_formal_parameter_selector_name is specified. Any
positional associations shall precede any named associations.
1. The generic actual parameter is either the
explicit_generic_actual_parameter given in a
generic_parameter_association for each formal, or the corresponding
default_expression or default_name if no generic_parameter_association is
given for the formal. When the meaning is clear from context, the term
``generic actual,'' or simply ``actual,'' is used as a synonym for
``generic actual parameter'' and also for the view denoted by one, or the
value of one.
Legality Rules
2. In a generic_instantiation for a particular kind of program unit
(package, procedure, or function), the name shall denote a generic unit
of the corresponding kind (generic package, generic procedure, or generic
function, respectively).
3. The generic_formal_parameter_selector_name of a generic_association shall
denote a generic_formal_parameter_declaration of the generic unit being
instantiated. If two or more formal subprograms have the same defining
name, then named associations are not allowed for the corresponding
actuals.
4. A generic_instantiation shall contain at most one generic_association for
each formal. Each formal without an association shall have a
default_expression or subprogram_default.
5. In a generic unit Legality Rules are enforced at compile time of the
generic_declaration and generic body, given the properties of the
formals. In the visible part and formal part of an instance, Legality
Rules are enforced at compile time of the generic_instantiation, given
the properties of the actuals. In other parts of an instance, Legality
Rules are not enforced; this rule does not apply when a given rule
explicitly specifies otherwise.
Static Semantics
6. A generic_instantiation declares an instance; it is equivalent to the
instance declaration (a package_declaration or subprogram_declaration)
immediately followed by the instance body, both at the place of the
instantiation.
7. The instance is a copy of the text of the template. Each use of a formal
parameter becomes (in the copy) a use of the actual, as explained below.
An instance of a generic package is a package, that of a generic
procedure is a procedure, and that of a generic function is a function.
8. The interpretation of each construct within a generic declaration or body
is determined using the overloading rules when that generic declaration
or body is compiled. In an instance, the interpretation of each (copied)
construct is the same, except in the case of a name that denotes the
generic_declaration or some declaration within the generic unit; the
corresponding name in the instance then denotes the corresponding copy of
the denoted declaration. The overloading rules do not apply in the
instance.
9. In an instance, a generic_formal_parameter_declaration declares a view
whose properties are identical to those of the actual, except as
specified in 12.4: ``Formal Objects'', and 12.6: ``Formal Subprograms''.
Similarly, for a declaration within a
generic_formal_parameter_declaration, the corresponding declaration in an
instance declares a view whose properties are identical to the
corresponding declaration within the declaration of the actual.
10. Implicit declarations are also copied, and a name that denotes an
implicit declaration in the generic denotes the corresponding copy in the
instance. However, for a type declared within the visible part of the
generic, a whole new set of primitive subprograms is implicitly declared
for use outside the instance, and may differ from the copied set if the
properties of the type in some way depend on the properties of some
actual type specified in the instantiation. For example, if the type in
the generic is derived from a formal private type, then in the instance
the type will inherit subprograms from the corresponding actual type.
11. These new implicit declarations occur immediately after the type
declaration in the instance, and override the copied ones. The copied
ones can be called only from within the instance; the new ones can be
called only from outside the instance, although for tagged types, the
body of a new one can be executed by a call to an old one.
12. In the visible part of an instance, an explicit declaration overrides an
implicit declaration if they are homographs, as described in 8.3. On the
other hand, an explicit declaration in the private part of an instance
overrides an implicit declaration in the instance, only if the
corresponding explicit declaration in the generic overrides a
corresponding implicit declaration in the generic. Corresponding rules
apply to the other kinds of overriding described in 8.3.
Post-Compilation Rules
13. Recursive generic instantiation is not allowed in the following sense: if
a given generic unit includes an instantiation of a second generic unit,
then the instance generated by this instantiation shall not include an
instance of the first generic unit (whether this instance is generated
directly, or indirectly by intermediate instantiations).
Dynamic Semantics
14. For the elaboration of a generic_instantiation, each generic_association
is first evaluated. If a default is used, an implicit generic_association
is assumed for this rule. These evaluations are done in an arbitrary
order, except that the evaluation for a default actual takes place after
the evaluation for another actual if the default includes a name that
denotes the other one. Finally, the instance declaration and body are
elaborated.
15. For the evaluation of a generic_association the generic actual parameter
is evaluated. Additional actions are performed in the case of a formal
object of mode in, see 12.4.
NOTES
16. (5) If a formal type is not tagged, then the type is treated as an
untagged type within the generic body. Deriving from such a type in a
generic body is permitted; the new type does not get a new tag value,
even if the actual is tagged. Overriding operations for such a derived
type cannot be dispatched to from outside the instance.
Examples
17. Examples of generic instantiations, see 12.1
18.
procedure Swap is new Exchange(Elem => Integer);
procedure Swap is new Exchange(Character);
-- Swap is overloaded
function Square is new Squaring(Integer);
-- "*" of Integer used by default
function Square is new Squaring
(Item => Matrix, "*" => Matrix_Product);
function Square is new Squaring
(Matrix, Matrix_Product); -- same as previous
19.
package Int_Vectors is new On_Vectors(Integer, Table, "+");
20. Examples of uses of instantiated units:
21.
Swap(A, B);
A := Square(A);
22.
T : Table(1 ┬╖┬╖ 5) := (10, 20, 30, 40, 50);
N : Integer := Int_Vectors.Sigma(T);
-- 150 (see 12.2: ``Generic Bodies'', for the body of Sigma)
23.
use Int_Vectors;
M : Integer := Sigma(T); -- 150
ΓòÉΓòÉΓòÉ 15.4. Formal Objects ΓòÉΓòÉΓòÉ
1. A generic formal object can be used to pass a value or variable to a
generic unit.
Syntax
2.
formal_object_declaration ::=
defining_identifier_list : mode subtype_mark
[:= default_expression];
Name Resolution Rules
3. The expected type for the default_expression, if any, of a formal object
is the type of the formal object.
4. For a generic formal object of mode in, the expected type for the actual
is the type of the formal.
5. For a generic formal object of mode in out, the type of the actual shall
resolve to the type of the formal.
Legality Rules
6. If a generic formal object has a default_expression, then the mode shall
be in (either explicitly or by default); otherwise, its mode shall be
either in or in out.
7. For a generic formal object of mode in, the actual shall be an
expression. For a generic formal object of mode in out, the actual shall
be a name that denotes a variable for which renaming is allowed (see
8.5.1).
8. The type of a generic formal object of mode in shall be nonlimited.
Static Semantics
9. A formal_object_declaration declares a generic formal object. The default
mode is in. For a formal object of mode in, the nominal subtype is the
one denoted by the subtype_mark in the declaration of the formal. For a
formal object of mode in out, its type is determined by the subtype_mark
in the declaration; its nominal subtype is nonstatic, even if the
subtype_mark denotes a static subtype.
10. In an instance, a formal_object_declaration of mode in declares a new
stand-alone constant object whose initialization expression is the
actual, whereas a formal_object_declaration of mode in out declares a
view whose properties are identical to those of the actual.
Dynamic Semantics
11. For the evaluation of a generic_association for a formal object of mode
in, a constant object is created, the value of the actual parameter is
converted to the nominal subtype of the formal object, and assigned to
the object, including any value adjustment -- see 7.6.
NOTES
12. (6) The constraints that apply to a generic formal object of mode in out
are those of the corresponding generic actual parameter (not those
implied by the subtype_mark that appears in the
formal_object_declaration). Therefore, to avoid confusion, it is
recommended that the name of a first subtype be used for the declaration
of such a formal object.
ΓòÉΓòÉΓòÉ 15.5. Formal Types ΓòÉΓòÉΓòÉ
1. A generic formal subtype can be used to pass to a generic unit a subtype
whose type is in a certain class of types.
Syntax
2.
formal_type_declaration ::=
type defining_identifier[discriminant_part] is
formal_type_definition;
3.
formal_type_definition ::=
formal_private_type_definition
| formal_derived_type_definition
| formal_discrete_type_definition
| formal_signed_integer_type_definition
| formal_modular_type_definition
| formal_floating_point_definition
| formal_ordinary_fixed_point_definition
| formal_decimal_fixed_point_definition
| formal_array_type_definition
| formal_access_type_definition
Legality Rules
4. For a generic formal subtype, the actual shall be a subtype_mark; it
denotes the (generic) actual subtype.
Static Semantics
5. A formal_type_declaration declares a (generic) formal type, and its first
subtype, the (generic) formal subtype.
6. The form of a formal_type_definition determines a class to which the
formal type belongs. For a formal_private_type_definition the reserved
words tagged and limited indicate the class, see 12.5.1. For a
formal_derived_type_definition the class is the derivation class rooted
at the ancestor type. For other formal types, the name of the syntactic
category indicates the class; a formal_discrete_type_definition defines a
discrete type, and so on.
Legality Rules
7. The actual type shall be in the class determined for the formal.
Static Semantics
8. The formal type also belongs to each class that contains the determined
class. The primitive subprograms of the type are as for any type in the
determined class. For a formal type other than a formal derived type,
these are the predefined operators of the type; they are implicitly
declared immediately after the declaration of the formal type. In an
instance, the copy of such an implicit declaration declares a view of the
predefined operator of the actual type, even if this operator has been
overridden for the actual type. The rules specific to formal derived
types are given in 12.5.1.
NOTES
9. (7) Generic formal types, like all types, are not named. Instead, a name
can denote a generic formal subtype. Within a generic unit, a generic
formal type is considered as being distinct from all other (formal or
nonformal) types.
10. (8) A discriminant_part is allowed only for certain kinds of types, and
therefore only for certain kinds of generic formal types (see 3.7).
Examples
11. Examples of generic formal types:
12.
type Item is private;
type Buffer(Length : Natural) is limited private;
13.
type Enum is (<>);
type Int is range <>;
type Angle is delta <>;
type Mass is digits <>;
14.
type Table is array (Enum) of Item;
15. Example of a generic formal part declaring a formal integer type:
16.
generic
type Rank is range <>;
First : Rank := Rank'First;
Second : Rank := First + 1;
-- the operator "+" of the type Rank
12.5.1 Formal Private and Derived Types
12.5.2 Formal Scalar Types
12.5.3 Formal Array Types
12.5.4 Formal Access Types
ΓòÉΓòÉΓòÉ 15.5.1. Formal Private and Derived Types ΓòÉΓòÉΓòÉ
1. The class determined for a formal private type can be either limited or
nonlimited, and either tagged or untagged; no more specific class is
known for such a type. The class determined for a formal derived type is
the derivation class rooted at the ancestor type.
Syntax
2.
formal_private_type_definition ::=
[[abstract] tagged] [limited] private
3.
formal_derived_type_definition ::=
[abstract] new subtype_mark [with private]
Legality Rules
4. If a generic formal type declaration has a known_discriminant_part, then
it shall not include a default_expression for a discriminant.
5. The ancestor subtype of a formal derived type is the subtype denoted by
the subtype_mark of the formal_derived_type_definition. For a formal
derived type declaration, the reserved words with private shall appear if
and only if the ancestor type is a tagged type; in this case the formal
derived type is a private extension of the ancestor type and the ancestor
shall not be a class-wide type. Similarly, the optional reserved word
abstract shall appear only if the ancestor type is a tagged type.
6. If the formal subtype is definite, then the actual subtype shall also be
definite.
7. For a generic formal derived type with no discriminant_part:
a. If the ancestor subtype is constrained, the actual subtype shall be
constrained, and shall be statically compatible with the ancestor;
b. If the ancestor subtype is an unconstrained access or composite
subtype, the actual subtype shall be unconstrained.
c. If the ancestor subtype is an unconstrained discriminated subtype,
then the actual shall have the same number of discriminants, and
each discriminant of the actual shall correspond to a discriminant
of the ancestor, in the sense of 3.7.
1. The declaration of a formal derived type shall not have a
known_discriminant_part. For a generic formal private type with a
known_discriminant_part:
a. The actual type shall be a type with the same number of
discriminants.
b. The actual subtype shall be unconstrained.
c. The subtype of each discriminant of the actual type shall statically
match the subtype of the corresponding discriminant of the formal
type.
1. For a generic formal type with an unknown_discriminant_part, the actual
may, but need not, have discriminants, and may be definite or indefinite.
Static Semantics
2. The class determined for a formal private type is as follows:
3.
Type Definition Determined Class
limited private the class of all types
private the class of all nonlimited types
tagged limited private the class of all tagged types
tagged private the class of all nonlimited tagged types
4. The presence of the reserved word abstract determines whether the actual
type may be abstract.
5. A formal private or derived type is a private or derived type,
respectively. A formal derived tagged type is a private extension. A
formal private or derived type is abstract if the reserved word abstract
appears in its declaration.
6. If the ancestor type is a composite type that is not an array type, the
formal type inherits components from the ancestor type (including
discriminants if a new discriminant_part is not specified), as for a
derived type defined by a derived_type_definition, see 3.4.
7. For a formal derived type, the predefined operators and inherited
user-defined subprograms are determined by the ancestor type, and are
implicitly declared at the earliest place, if any, within the immediate
scope of the formal type, where the corresponding primitive subprogram of
the ancestor is visible, see 7.3.1. In an instance, the copy of such an
implicit declaration declares a view of the corresponding primitive
subprogram of the ancestor, even if this primitive has been overridden
for the actual type. In the case of a formal private extension, however,
the tag of the formal type is that of the actual type, so if the tag in a
call is statically determined to be that of the formal type, the body
executed will be that corresponding to the actual type.
8. For a prefix S that denotes a formal indefinite subtype, the following
attribute is defined:
9. S'Definite
S'Definite yields True if the actual subtype corresponding to
S is definite; otherwise it yields False. The value of this
attribute is of the predefined type Boolean.
NOTES
10. (9) In accordance with the general rule that the actual type shall belong
to the class determined for the formal, see 12.5: ``Formal Types''.:
a. If the formal type is nonlimited, then so shall be the actual;
b. For a formal derived type, the actual shall be in the class rooted
at the ancestor subtype.
1. (10) The actual type can be abstract only if the formal type is abstract
(see 3.9.3).
2. (11) If the formal has a discriminant_part, the actual can be either
definite or indefinite. Otherwise, the actual has to be definite.
ΓòÉΓòÉΓòÉ 15.5.2. Formal Scalar Types ΓòÉΓòÉΓòÉ
1. A formal scalar type is one defined by any of the formal_type_definitions
in this subclause. The class determined for a formal scalar type is
discrete, signed integer, modular, floating point, ordinary fixed point,
or decimal.
Syntax
2.
formal_discrete_type_definition ::= (<>)
3.
formal_signed_integer_type_definition ::= range <>
4.
formal_modular_type_definition ::= mod <>
5.
formal_floating_point_definition ::= digits <>
6.
formal_ordinary_fixed_point_definition ::= delta <>
7.
formal_decimal_fixed_point_definition ::= delta <> digits <>
Legality Rules
8. The actual type for a formal scalar type shall not be a nonstandard
numeric type.
NOTES
9. (12) The actual type shall be in the class of types implied by the
syntactic category of the formal type definition, see 12.5: ``Formal
Types''. For example, the actual for a formal_modular_type_definition
shall be a modular type.
ΓòÉΓòÉΓòÉ 15.5.3. Formal Array Types ΓòÉΓòÉΓòÉ
1. The class determined for a formal array type is the class of all array
types.
Syntax
2.
formal_array_type_definition ::= array_type_definition
Legality Rules
3. The only form of discrete_subtype_definition that is allowed within the
declaration of a generic formal (constrained) array subtype is a
subtype_mark.
4. For a formal array subtype, the actual subtype shall satisfy the
following conditions:
a. The formal array type and the actual array type shall have the same
dimensionality; the formal subtype and the actual subtype shall be
either both constrained or both unconstrained.
b. For each index position, the index types shall be the same, and the
index subtypes (if unconstrained), or the index ranges (if
constrained), shall statically match, see 4.9.1.
c. The component subtypes of the formal and actual array types shall
statically match.
d. If the formal type has aliased components, then so shall the actual.
Examples
1. Example of formal array types:
2.
-- given the generic package
3.
generic
type Item is private;
type Index is (<>);
type Vector is array (Index range <>) of Item;
type Table is array (Index) of Item;
package P is
┬╖┬╖┬╖
end P;
4.
-- and the types
5.
type Mix is array (Color range <>) of Boolean;
type Option is array (Color) of Boolean;
6.
-- then Mix can match Vector and Option can match Table
7.
package R is new P(Item => Boolean, Index => Color,
Vector => Mix, Table => Option);
8.
-- Note that Mix cannot match Table and Option cannot match Vector
ΓòÉΓòÉΓòÉ 15.5.4. Formal Access Types ΓòÉΓòÉΓòÉ
1. The class determined for a formal access type is the class of all access
types.
Syntax
2.
formal_access_type_definition ::= access_type_definition
Legality Rules
3. For a formal access-to-object type, the designated subtypes of the formal
and actual types shall statically match.
4. If and only if the general_access_modifier constant applies to the
formal, the actual shall be an access-to-constant type. If the
general_access_modifier all applies to the formal, then the actual shall
be a general access-to-variable type, see 3.10.
5. For a formal access-to-subprogram subtype, the designated profiles of the
formal and the actual shall be mode-conformant, and the calling
convention of the actual shall be protected if and only if that of the
formal is protected.
Examples
6. Example of formal access types:
7.
-- the formal types of the generic package
8.
generic
type Node is private;
type Link is access Node;
package P is
┬╖┬╖┬╖
end P;
9.
-- can be matched by the actual types
10.
type Car;
type Car_Name is access Car;
11.
type Car is
record
Pred, Succ : Car_Name;
Number : License_Number;
Owner : Person;
end record;
12.
-- in the following generic instantiation
13.
package R is new P(Node => Car, Link => Car_Name);
ΓòÉΓòÉΓòÉ 15.6. Formal Subprograms ΓòÉΓòÉΓòÉ
1. Formal subprograms can be used to pass callable entities to a generic
unit.
Syntax
2.
formal_subprogram_declaration ::=
with subprogram_specification [is subprogram_default];
3.
subprogram_default ::= default_name | <>
4.
default_name ::= name
Name Resolution Rules
5. The expected profile for the default_name, if any, is that of the formal
subprogram.
6. For a generic formal subprogram, the expected profile for the actual is
that of the formal subprogram.
Legality Rules
7. The profiles of the formal and any named default shall be
mode-conformant.
8. The profiles of the formal and actual shall be mode-conformant.
Static Semantics
9. A formal_subprogram_declaration declares a generic formal subprogram. The
types of the formal parameters and result, if any, of the formal
subprogram are those determined by the subtype_marks given in the
formal_subprogram_declaration; however, independent of the particular
subtypes that are denoted by the subtype_marks, the nominal subtypes of
the formal parameters and result, if any, are defined to be nonstatic,
and unconstrained if of an array type (no applicable index constraint is
provided in a call on a formal subprogram). In an instance, a
formal_subprogram_declaration declares a view of the actual. The profile
of this view takes its subtypes and calling convention from the original
profile of the actual entity, while taking the formal parameter names and
default_expressions from the profile given in the
formal_subprogram_declaration. The view is a function or procedure, never
an entry.
10. If a generic unit has a subprogram_default specified by a box, and the
corresponding actual parameter is omitted, then it is equivalent to an
explicit actual parameter that is a usage name identical to the defining
name of the formal.
NOTES
11. (13) The matching rules for formal subprograms state requirements that
are similar to those applying to subprogram_renaming_declarations (see
8.5.4). In particular, the name of a parameter of the formal subprogram
need not be the same as that of the corresponding parameter of the actual
subprogram; similarly, for these parameters, default_expressions need not
correspond.
12. (14) The constraints that apply to a parameter of a formal subprogram are
those of the corresponding formal parameter of the matching actual
subprogram (not those implied by the corresponding subtype_mark in the
_specification of the formal subprogram). A similar remark applies to the
result of a function. Therefore, to avoid confusion, it is recommended
that the name of a first subtype be used in any declaration of a formal
subprogram.
13. (15) The subtype specified for a formal parameter of a generic formal
subprogram can be any visible subtype, including a generic formal subtype
of the same generic_formal_part.
14. (16) A formal subprogram is matched by an attribute of a type if the
attribute is a function with a matching specification. An enumeration
literal of a given type matches a parameterless formal function whose
result type is the given type.
15. (17) A default_name denotes an entity that is visible or directly visible
at the place of the generic_declaration; a box used as a default is
equivalent to a name that denotes an entity that is directly visible at
the place of the _instantiation.
16. (18) The actual subprogram cannot be abstract, see 3.9.3.
Examples
17. Examples of generic formal subprograms:
18.
with function "+"(X, Y : Item) return Item is <>;
with function Image(X : Enum) return String is Enum'Image;
with procedure Update is Default_Update;
19.
-- given the generic procedure declaration
20.
generic
with procedure Action (X : in Item);
procedure Iterate(Seq : in Item_Sequence);
21.
-- and the procedure
22.
procedure Put_Item(X : in Item);
23.
-- the following instantiation is possible
24.
procedure Put_List is new Iterate(Action => Put_Item);
ΓòÉΓòÉΓòÉ 15.7. Formal Packages ΓòÉΓòÉΓòÉ
1. Formal packages can be used to pass packages to a generic unit. The
formal_package_declaration declares that the formal package is an
instance of a given generic package. Upon instantiation, the actual
package has to be an instance of that generic package.
Syntax
2.
formal_package_declaration ::=
with package defining_identifier is new
generic_package_name formal_package_actual_part;
3.
formal_package_actual_part ::= (<>) | [generic_actual_part]
Legality Rules
4. The generic_package_name shall denote a generic package (the template for
the formal package); the formal package is an instance of the template.
5. The actual shall be an instance of the template. If the
formal_package_actual_part is (<>), then the actual may be any instance
of the template; otherwise, each actual parameter of the actual instance
shall match the corresponding actual parameter of the formal package
(whether the actual parameter is given explicitly or by default), as
follows:
a. For a formal object of mode in the actuals match if they are static
expressions with the same value, or if they statically denote the
same constant, or if they are both the literal null.
b. For a formal subtype, the actuals match if they denote statically
matching subtypes.
c. For other kinds of formals, the actuals match if they statically
denote the same entity.
Static Semantics
1. A formal_package_declaration declares a generic formal package.
2. The visible part of a formal package includes the first list of
basic_declarative_items of the package_specification. In addition, if the
formal_package_actual_part is (<>), it also includes the
generic_formal_part of the template for the formal package.
ΓòÉΓòÉΓòÉ 15.8. Example of a Generic Package ΓòÉΓòÉΓòÉ
1. The following example provides a possible formulation of stacks by means
of a generic package. The size of each stack and the type of the stack
elements are provided as generic formal parameters.
Examples
1.
generic
Size : Positive;
type Item is private;
package Stack is
procedure Push(E : in Item);
procedure Pop (E : out Item);
Overflow, Underflow : exception;
end Stack;
2.
package body Stack is
3.
type Table is array (Positive range <>) of Item;
Space : Table(1 ┬╖┬╖ Size);
Index : Natural := 0;
4.
procedure Push(E : in Item) is
begin
if Index >= Size then
raise Overflow;
end if;
Index := Index + 1;
Space(Index) := E;
end Push;
5.
procedure Pop(E : out Item) is
begin
if Index = 0 then
raise Underflow;
end if;
E := Space(Index);
Index := Index - 1;
end Pop;
6.
end Stack;
7. Instances of this generic package can be obtained as follows:
8.
package Stack_Int is new Stack(Size => 200, Item => Integer);
package Stack_Bool is new Stack(100, Boolean);
9. Thereafter, the procedures of the instantiated packages can be called as
follows:
10.
Stack_Int.Push(N);
Stack_Bool.Push(True);
11. Alternatively, a generic formulation of the type Stack can be given as
follows (package body omitted):
12.
generic
type Item is private;
package On_Stacks is
type Stack(Size : Positive) is limited private;
procedure Push(S : in out Stack; E : in Item);
procedure Pop (S : in out Stack; E : out Item);
Overflow, Underflow : exception;
private
type Table is array (Positive range <>) of Item;
type Stack(Size : Positive) is
record
Space : Table(1 ┬╖┬╖ Size);
Index : Natural := 0;
end record;
end On_Stacks;
13. In order to use such a package, an instance has to be created and
thereafter stacks of the corresponding type can be declared:
14.
declare
package Stack_Real is new On_Stacks(Real); use Stack_Real;
S : Stack(100);
begin
┬╖┬╖┬╖
Push(S, 2.54);
┬╖┬╖┬╖
end;
ΓòÉΓòÉΓòÉ 16. Representation Issues ΓòÉΓòÉΓòÉ
1. This section describes features for querying and controlling aspects of
representation and for interfacing to hardware.
13.1 Representation Items
13.2 Pragma Pack
13.3 Representation Attributes
13.4 Enumeration Representation Clauses
13.5 Record Layout
13.6 Change of Representation
13.7 The Package System
13.8 Machine Code Insertions
13.9 Unchecked Type Conversions
13.10 Unchecked Access Value Creation
13.11 Storage Management
13.12 Pragma Restrictions
13.13 Streams
13.14 Freezing Rules --- The Detailed Node Listing ---
13.1 Representation Items
13.2 Pragma Pack
13.3 Representation Attributes
13.4 Enumeration Representation Clauses
13.5 Record Layout
13.5.1 Record Representation Clauses
13.5.2 Storage Place Attributes
13.5.3 Bit Ordering
13.6 Change of Representation
13.7 The Package System
13.7.1 The Package System.Storage_Elements
13.7.2 The Package System.Address_To_Access_Conversions
13.8 Machine Code Insertions
13.9 Unchecked Type Conversions
13.9.1 Data Validity
13.9.2 The Valid Attribute
13.10 Unchecked Access Value Creation
13.11 Storage Management
13.11.1 The Max_Size_In_Storage_Elements Attribute
13.11.2 Unchecked Storage Deallocation
13.11.3 Pragma Controlled
13.12 Pragma Restrictions
13.13 Streams
13.13.1 The Package Streams
13.13.2 Stream-Oriented Attributes
13.14 Freezing Rules
ΓòÉΓòÉΓòÉ 16.1. Representation Items ΓòÉΓòÉΓòÉ
1. There are three kinds of representation items: representation_clauses,
component_clauses, and representation pragmas. Representation items
specify how the types and other entities of the language are to be mapped
onto the underlying machine. They can be provided to give more efficient
representation or to interface with features that are outside the domain
of the language (for example, peripheral hardware). Representation items
also specify other specifiable properties of entities. A representation
item applies to an entity identified by a local_name, which denotes an
entity declared local to the current declarative region, or a library
unit declared immediately preceding a representation pragma in a
compilation.
Syntax
2.
representation_clause ::=
attribute_definition_clause
| enumeration_representation_clause
| record_representation_clause
| at_clause
3.
local_name ::=
direct_name
| direct_name'attribute_designator
| library_unit_name
a. A representation pragma is allowed only at places where a
representation_clause or compilation_unit is allowed.
Name Resolution Rules
1. In a representation item, if the local_name is a direct_name, then it
shall resolve to denote a declaration (or, in the case of a pragma, one
or more declarations) that occurs immediately within the same
declarative_region as the representation item. If the local_name has an
attribute_designator, then it shall resolve to denote an
implementation-defined component, see 13.5.1, or a class-wide type
implicitly declared immediately within the same declarative_region as the
representation item. A local_name that is a library_unit_name (only
permitted in a representation pragma) shall resolve to denote the
library_item that immediately precedes (except for other pragmas) the
representation pragma.
Legality Rules
2. The local_name of a representation_clause or representation pragma shall
statically denote an entity (or, in the case of a pragma, one or more
entities) declared immediately preceding it in a compilation, or within
the same declarative_part, package_specification, task_definition,
protected_definition, or record_definition as the representation item. If
a local_name denotes a local callable entity, it may do so through a
local subprogram_renaming_declaration (as a way to resolve ambiguity in
the presence of overloading); otherwise, the local_name shall not denote
a renaming_declaration.
3. The representation of an object consists of a certain number of bits (the
size of the object). These are the bits that are normally read or updated
by the machine code when loading, storing, or operating-on the value of
the object. This includes some padding bits, when the size of the object
is greater than the size of its subtype. Such padding bits are considered
to be part of the representation of the object, rather than being gaps
between objects, if these bits are normally read and updated.
4. A representation item directly specifies an aspect of representation of
the entity denoted by the local_name, except in the case of a
type-related representation item, whose local_name shall denote a first
subtype, and which directly specifies an aspect of the subtype's type. A
representation item that names a subtype is either subtype-specific (Size
and Alignment clauses) or type-related (all others). Subtype-specific
aspects may differ for different subtypes of the same type.
5. A representation item that directly specifies an aspect of a subtype or
type shall appear after the type is completely defined, see 3.11.1, and
before the subtype or type is frozen, see 13.14. If a representation item
is given that directly specifies an aspect of an entity, then it is
illegal to give another representation item that directly specifies the
same aspect of the entity.
6. For an untagged derived type, no type-related representation items are
allowed if the parent type is a by-reference type, or has any
user-defined primitive subprograms.
7. Representation aspects of a generic formal parameter are the same as
those of the actual. A type-related representation item is not allowed
for a descendant of a generic formal untagged type.
8. A representation item that specifies the Size for a given subtype, or the
size or storage place for an object (including a component) of a given
subtype, shall allow for enough storage space to accommodate any value of
the subtype.
9. A representation item that is not supported by the implementation is
illegal, or raises an exception at run time.
Static Semantics
10. If two subtypes statically match, then their subtype-specific aspects
(Size and Alignment) are the same.
11. A derived type inherits each type-related aspect of its parent type that
was directly specified before the declaration of the derived type, or (in
the case where the parent is derived) that was inherited by the parent
type from the grandparent type. A derived subtype inherits each
subtype-specific aspect of its parent subtype that was directly specified
before the declaration of the derived type, or (in the case where the
parent is derived) that was inherited by the parent subtype from the
grandparent subtype, but only if the parent subtype statically matches
the first subtype of the parent type. An inherited aspect of
representation is overridden by a subsequent representation item that
specifies the same aspect of the type or subtype.
12. Each aspect of representation of an entity is as follows:
a. If the aspect is specified for the entity, meaning that it is either
directly specified or inherited, then that aspect of the entity is
as specified, except in the case of Storage_Size, which specifies a
minimum.
b. If an aspect of representation of an entity is not specified, it is
chosen by default in an unspecified manner.
Dynamic Semantics
1. For the elaboration of a representation_clause, any evaluable constructs
within it are evaluated.
Implementation Permissions
2. An implementation may interpret aspects of representation in an
implementation-defined manner. An implementation may place
implementation-defined restrictions on representation items. A
recommended level of support is specified for representation items and
related features in each subclause. These recommendations are changed to
requirements for implementations that support the Systems Programming
Annex, see C.2: ``Required Representation Support''.
Implementation Advice
3. The recommended level of support for all representation items is
qualified as follows:
a. An implementation need not support representation items containing
nonstatic expressions, except that an implementation should support
a representation item for a given entity if each nonstatic
expression in the representation item is a name that statically
denotes a constant declared before the entity.
b. An implementation need not support a specification for the Size for
a given composite subtype, nor the size or storage place for an
object (including a component) of a given composite subtype, unless
the constraints on the subtype and its composite subcomponents (if
any) are all static constraints.
c. An aliased component, or a component whose type is by-reference,
should always be allocated at an addressable location.
ΓòÉΓòÉΓòÉ 16.2. Pragma Pack ΓòÉΓòÉΓòÉ
1. A pragma Pack specifies that storage minimization should be the main
criterion when selecting the representation of a composite type.
Syntax
2. The form of a pragma Pack is as follows:
3.
pragma Pack(first_subtype_local_name);
Legality Rules
4. The first_subtype_local_name of a pragma Pack shall denote a composite
subtype.
Static Semantics
5. A pragma Pack specifies the packing aspect of representation; the type
(or the extension part) is said to be packed. For a type extension, the
parent part is packed as for the parent type, and a pragma Pack causes
packing only of the extension part.
Implementation Advice
6. If a type is packed, then the implementation should try to minimize
storage allocated to objects of the type, possibly at the expense of
speed of accessing components, subject to reasonable complexity in
addressing calculations.
7. The recommended level of support for pragma Pack is:
a. For a packed record type, the components should be packed as tightly
as possible subject to the Sizes of the component subtypes, and
subject to any record_representation_clause that applies to the
type; the implementation may, but need not, reorder components or
cross aligned word boundaries to improve the packing. A component
whose Size is greater than the word size may be allocated an
integral number of words.
b. For a packed array type, if the component subtype's Size is less
than or equal to the word size, and Component_Size is not specified
for the type, Component_Size should be less than or equal to the
Size of the component subtype, rounded up to the nearest factor of
the word size.
ΓòÉΓòÉΓòÉ 16.3. Representation Attributes ΓòÉΓòÉΓòÉ
1. The values of certain implementation-dependent characteristics can be
obtained by interrogating appropriate representation attributes. Some of
these attributes are specifiable via an attribute_definition_clause.
Syntax
2.
attribute_definition_clause ::=
for local_name'attribute_designator use expression;
| for local_name'attribute_designator use name;
Name Resolution Rules
3. For an attribute_definition_clause that specifies an attribute that
denotes a value, the form with an expression shall be used. Otherwise,
the form with a name shall be used.
4. For an attribute_definition_clause that specifies an attribute that
denotes a value or an object, the expected type for the expression or
name is that of the attribute. For an attribute_definition_clause that
specifies an attribute that denotes a subprogram, the expected profile
for the name is the profile required for the attribute. For an
attribute_definition_clause that specifies an attribute that denotes some
other kind of entity, the name shall resolve to denote an entity of the
appropriate kind.
Legality Rules
5. An attribute_designator is allowed in an attribute_definition_clause only
if this International Standard explicitly allows it, or for an
implementation-defined attribute if the implementation allows it. Each
specifiable attribute constitutes an aspect of representation.
6. For an attribute_definition_clause that specifies an attribute that
denotes a subprogram, the profile shall be mode conformant with the one
required for the attribute, and the convention shall be Ada. Additional
requirements are defined for particular attributes.
Static Semantics
7. A Size clause is an attribute_definition_clause whose
attribute_designator is Size. Similar definitions apply to the other
specifiable attributes.
8. A storage element is an addressable element of storage in the machine. A
word is the largest amount of storage that can be conveniently and
efficiently manipulated by the hardware, given the implementation's
run-time model. A word consists of an integral number of storage
elements.
9. The following attributes are defined:
10. For a prefix X that denotes an object, program unit, or label:
11. X'Address
Denotes the address of the first of the storage elements
allocated to X. For a program unit or label, this value
refers to the machine code associated with the corresponding
body or statement. The value of this attribute is of type
System.Address.
12.
Address may be specified for stand-alone objects and for
program units via an attribute_definition_clause.
Erroneous Execution
13. If an Address is specified, it is the programmer's responsibility to
ensure that the address is valid; otherwise, program execution is
erroneous.
Implementation Advice
14. For an array X, X'Address should point at the first component of the
array, and not at the array bounds.
15. The recommended level of support for the Address attribute is:
a. X'Address should produce a useful result if X is an object that is
aliased or of a by-reference type, or is an entity whose Address has
been specified.
b. An implementation should support Address clauses for imported
subprograms.
c. Objects (including subcomponents) that are aliased or of a
by-reference type should be allocated on storage element boundaries.
d. If the Address of an object is specified, or it is imported or
exported, then the implementation should not perform optimizations
based on assumptions of no aliases.
NOTES
1. (1) The specification of a link name in a pragma Export, see B.1 for a
subprogram or object is an alternative to explicit specification of its
link-time address, allowing a link-time directive to place the subprogram
or object within memory.
2. (2) The rules for the Size attribute imply, for an aliased object X, that
if X'Size = Storage_Unit, then X'Address points at a storage element
containing all of the bits of X, and only the bits of X.
Static Semantics
3. For a prefix X that denotes a subtype or object:
4. X'Alignment
The Address of an object that is allocated under control of
the implementation is an integral multiple of the Alignment
of the object (that is, the Address modulo the Alignment is
zero). The offset of a record component is a multiple of the
Alignment of the component. For an object that is not
allocated under control of the implementation (that is, one
that is imported, that is allocated by a user-defined
allocator, whose Address has been specified, or is designated
by an access value returned by an instance of
Unchecked_Conversion), the implementation may assume that the
Address is an integral multiple of its Alignment. The
implementation shall not assume a stricter alignment.
5.
The value of this attribute is of type
universal_integer, and nonnegative; zero means that the
object is not necessarily aligned on a storage element
boundary.
6.
Alignment may be specified for first subtypes and
stand-alone objects via an attribute_definition_clause; the
expression of such a clause shall be static, and its value
nonnegative. If the Alignment of a subtype is specified,
then the Alignment of an object of the subtype is at least as
strict, unless the object's Alignment is also specified. The
Alignment of an object created by an allocator is that of the
designated subtype.
7.
If an Alignment is specified for a composite subtype or
object, this Alignment shall be equal to the least common
multiple of any specified Alignments of the subcomponent
subtypes, or an integer multiple thereof.
Erroneous Execution
8. Program execution is erroneous if an Address clause is given that
conflicts with the Alignment.
9. If the Alignment is specified for an object that is not allocated under
control of the implementation, execution is erroneous if the object is
not aligned according to the Alignment.
Implementation Advice
10. The recommended level of support for the Alignment attribute for subtypes
is:
a. An implementation should support specified Alignments that are
factors and multiples of the number of storage elements per word,
subject to the following:
b. An implementation need not support specified Alignments for
combinations of Sizes and Alignments that cannot be easily loaded
and stored by available machine instructions.
c. An implementation need not support specified Alignments that are
greater than the maximum Alignment the implementation ever returns
by default.
1. The recommended level of support for the Alignment attribute for objects
is:
a. Same as above, for subtypes, but in addition:
b. For stand-alone library-level objects of statically constrained
subtypes, the implementation should support all Alignments supported
by the target linker. For example, page alignment is likely to be
supported for such objects, but not for subtypes.
NOTES
1. (3) Alignment is a subtype-specific attribute.
2. (4) The Alignment of a composite object is always equal to the least
common multiple of the Alignments of its components, or a multiple
thereof.
3. (5) A component_clause, Component_Size clause, or a pragma Pack can
override a specified Alignment.
Static Semantics
4. For a prefix X that denotes an object:
5. X'Size
Denotes the size in bits of the representation of the object.
The value of this attribute is of the type universal_integer.
a. Size may be specified for stand-alone objects via an
attribute_definition_clause; the expression of such a clause shall
be static and its value nonnegative.
Implementation Advice
1. The recommended level of support for the Size attribute of objects is:
a. A Size clause should be supported for an object if the specified
Size is at least as large as its subtype's Size, and corresponds to
a size in storage elements that is a multiple of the object's
Alignment (if the Alignment is nonzero).
Static Semantics
1. For every subtype S:
2. S'Size
If S is definite, denotes the size (in bits) that the
implementation would choose for the following objects of
subtype S:
a. A record component of subtype S when the record type is packed.
b. The formal parameter of an instance of Unchecked_Conversion that
converts from subtype S to some other subtype.
c. If S is indefinite, the meaning is implementation defined. The value
of this attribute is of the type universal_integer. The Size of an
object is at least as large as that of its subtype, unless the
object's Size is determined by a Size clause, a component_clause, or
a Component_Size clause. Size may be specified for first subtypes
via an attribute_definition_clause; the expression of such a clause
shall be static and its value nonnegative.
Implementation Requirements
1. In an implementation, Boolean'Size shall be 1.
Implementation Advice
2. If the Size of a subtype is specified, and allows for efficient
independent addressability, see 9.10, on the target architecture, then
the Size of the following objects of the subtype should equal the Size of
the subtype:
a. Aliased objects (including components).
b. Unaliased components, unless the Size of the component is determined
by a component_clause or Component_Size clause.
1. A Size clause on a composite subtype should not affect the internal
layout of components.
2. The recommended level of support for the Size attribute of subtypes is:
a. The Size (if not specified) of a static discrete or fixed point
subtype should be the number of bits needed to represent each value
belonging to the subtype using an unbiased representation, leaving
space for a sign bit only if the subtype contains negative values.
If such a subtype is a first subtype, then an implementation should
support a specified Size for it that reflects this representation.
b. For a subtype implemented with levels of indirection, the Size
should include the size of the pointers, but not the size of what
they point at.
NOTES
1. (6) Size is a subtype-specific attribute.
2. (7) A component_clause or Component_Size clause can override a specified
Size. A pragma Pack cannot.
Static Semantics
3. For a prefix T that denotes a task object (after any implicit
dereference):
4. T'Storage_Size
Denotes the number of storage elements reserved for the task.
The value of this attribute is of the type universal_integer.
The Storage_Size includes the size of the task's stack, if
any. The language does not specify whether or not it
includes other storage associated with the task (such as the
``task control block'' used by some implementations.) If a
pragma Storage_Size is given, the value of the Storage_Size
attribute is at least the value specified in the pragma.
5. A pragma Storage_Size specifies the amount of storage to be reserved for
the execution of a task.
Syntax
6. The form of a pragma Storage_Size is as follows:
7.
pragma Storage_Size(expression);
a. A pragma Storage_Size is allowed only immediately within a
task_definition.
Name Resolution Rules
1. The expression of a pragma Storage_Size is expected to be of any integer
type.
Dynamic Semantics
2. A pragma Storage_Size is elaborated when an object of the type defined by
the immediately enclosing task_definition is created. For the elaboration
of a pragma Storage_Size, the expression is evaluated; the Storage_Size
attribute of the newly created task object is at least the value of the
expression.
3. At the point of task object creation, or upon task activation,
Storage_Error is raised if there is insufficient free storage to
accommodate the requested Storage_Size. Static Semantics
4. For a prefix X that denotes an array subtype or array object (after any
implicit dereference):
5. X'Component_Size
Denotes the size in bits of components of the type of X. The
value of this attribute is of type universal_integer.
a. Component_Size may be specified for array types via an
attribute_definition_clause; the expression of such a clause shall
be static, and its value nonnegative.
Implementation Advice
1. The recommended level of support for the Component_Size attribute is:
a. An implementation need not support specified Component_Sizes that
are less than the Size of the component subtype.
b. An implementation should support specified Component_Sizes that are
factors and multiples of the word size. For such Component_Sizes,
the array should contain no gaps between components. For other
Component_Sizes (if supported), the array should contain no gaps
between components when packing is also specified; the
implementation should forbid this combination in cases where it
cannot support a no-gaps representation.
Static Semantics
1. For every subtype S of a tagged type T (specific or class-wide), the
following attribute is defined:
2. S'External_Tag
S'External_Tag denotes an external string representation for
S'Tag; it is of the predefined type String. External_Tag may
be specified for a specific tagged type via an
attribute_definition_clause; the expression of such a
clause shall be static. The default external tag
representation is implementation defined. See 3.9.2, and
13.13.2.
Implementation Requirements
3. In an implementation, the default external tag for each specific tagged
type declared in a partition shall be distinct, so long as the type is
declared outside an instance of a generic body. If the compilation unit
in which a given tagged type is declared, and all compilation units on
which it semantically depends, are the same in two different partitions,
then the external tag for the type shall be the same in the two
partitions. What it means for a compilation unit to be the same in two
different partitions is implementation defined. At a minimum, if the
compilation unit is not recompiled between building the two different
partitions that include it, the compilation unit is considered the same
in the two partitions.
NOTES
4. (8) The following language-defined attributes are specifiable, at least
for some of the kinds of entities to which they apply: Address, Size,
Component_Size, Alignment, External_Tag, Small, Bit_Order, Storage_Pool,
Storage_Size, Write, Output, Read, Input, and Machine_Radix.
5. (9) It follows from the general rules in 13.1, that if one writes ``for
X'Size use Y;'' then the X'Size attribute_reference will return Y
(assuming the implementation allows the Size clause). The same is true
for all of the specifiable attributes except Storage_Size.
Examples
6. Examples of attribute definition clauses:
7.
Byte : constant := 8;
Page : constant := 2**12;
8.
type Medium is range 0 ┬╖┬╖ 65_000;
for Medium'Size use 2*Byte;
for Medium'Alignment use 2;
Device_Register : Medium;
for Device_Register'Size use Medium'Size;
for Device_Register'Address use
System.Storage_Elements.To_Address(16#FFFF_0020#);
9.
type Short is delta 0.01 range -100.0 ┬╖┬╖ 100.0;
for Short'Size use 15;
10.
for Car_Name'Storage_Size use
-- specify access type's storage pool size
2000*((Car'Size/System.Storage_Unit) +1);
-- approximately 2000 cars
11.
function My_Read(Stream : access Ada.Streams.Root_Stream_Type'Class)
return T;
for T'Read use My_Read; -- see 13.13.2
NOTES
12. (10) Notes on the examples: In the Size clause for Short, fifteen bits is
the minimum necessary, since the type definition requires Short'Small <=
2**(-7).
ΓòÉΓòÉΓòÉ 16.4. Enumeration Representation Clauses ΓòÉΓòÉΓòÉ
1. An enumeration_representation_clause specifies the internal codes for
enumeration literals.
Syntax
2.
enumeration_representation_clause ::=
for first_subtype_local_name use enumeration_aggregate;
3.
enumeration_aggregate ::= array_aggregate
Name Resolution Rules
4. The enumeration_aggregate shall be written as a one-dimensional
array_aggregate, for which the index subtype is the unconstrained subtype
of the enumeration type, and each component expression is expected to be
of any integer type.
Legality Rules
5. The first_subtype_local_name of an enumeration_representation_clause
shall denote an enumeration subtype.
6. The expressions given in the array_aggregate shall be static, and shall
specify distinct integer codes for each value of the enumeration type;
the associated integer codes shall satisfy the predefined ordering
relation of the type.
Static Semantics
7. An enumeration_representation_clause specifies the coding aspect of
representation. The coding consists of the internal code for each
enumeration literal, that is, the integral value used internally to
represent each literal.
Implementation Requirements
8. For nonboolean enumeration types, if the coding is not specified for the
type, then for each value of the type, the internal code shall be equal
to its position number.
Implementation Advice
9. The recommended level of support for enumeration_representation_clauses
is:
a. An implementation should support at least the internal codes in the
range System.Min_Int┬╖┬╖System.Max_Int. An implementation need not
support enumeration_representation_clauses for boolean types.
NOTES
1. (11) Unchecked_Conversion may be used to query the internal codes used
for an enumeration type. The attributes of the type, such as Succ, Pred,
and Pos, are unaffected by the representation_clause. For example, Pos
always returns the position number, not the internal integer code that
might have been specified in a representation_clause.
Examples
2. Example of an enumeration representation clause:
3.
type Mix_Code is (ADD, SUB, MUL, LDA, STA, STZ);
4.
for Mix_Code use
(ADD => 1, SUB => 2, MUL => 3, LDA => 8, STA => 24, STZ =>33);
ΓòÉΓòÉΓòÉ 16.5. Record Layout ΓòÉΓòÉΓòÉ
1. The (record) layout aspect of representation consists of the storage
places for some or all components, that is, storage place attributes of
the components. The layout can be specified with a
record_representation_clause.
13.5.1 Record Representation Clauses
13.5.2 Storage Place Attributes
13.5.3 Bit Ordering
ΓòÉΓòÉΓòÉ 16.5.1. Record Representation Clauses ΓòÉΓòÉΓòÉ
1. A record_representation_clause specifies the storage representation of
records and record extensions, that is, the order, position, and size of
components (including discriminants, if any).
Syntax
2.
record_representation_clause ::=
for first_subtype_local_name use
record [mod_clause]
{component_clause}
end record;
3.
component_clause ::=
component_local_name at position range first_bit ┬╖┬╖ last_bit;
4.
position ::= static_expression
5.
first_bit ::= static_simple_expression
6.
last_bit ::= static_simple_expression
Name Resolution Rules
7. Each position, first_bit, and last_bit is expected to be of any integer
type.
Legality Rules
8. The first_subtype_local_name of a record_representation_clause shall
denote a specific nonlimited record or record extension subtype.
9. If the component_local_name is a direct_name, the local_name shall denote
a component of the type. For a record extension, the component shall not
be inherited, and shall not be a discriminant that corresponds to a
discriminant of the parent type. If the component_local_name has an
attribute_designator, the direct_name of the local_name shall denote
either the declaration of the type or a component of the type, and the
attribute_designator shall denote an implementation-defined implicit
component of the type.
10. The position, first_bit, and last_bit shall be static expressions. The
value of position and first_bit shall be nonnegative. The value of
last_bit shall be no less than first_bit - 1.
11. At most one component_clause is allowed for each component of the type,
including for each discriminant (component_clauses may be given for some,
all, or none of the components). Storage places within a component_list
shall not overlap, unless they are for components in distinct variants of
the same variant_part.
12. A name that denotes a component of a type is not allowed within a
record_representation_clause for the type, except as the
component_local_name of a component_clause.
Static Semantics
13. A record_representation_clause (without the mod_clause) specifies the
layout. The storage place attributes, see 13.5.2, are taken from the
values of the position, first_bit, and last_bit expressions after
normalizing those values so that first_bit is less than Storage_Unit.
14. A record_representation_clause for a record extension does not override
the layout of the parent part; if the layout was specified for the parent
type, it is inherited by the record extension.
Implementation Permissions
15. An implementation may generate implementation-defined components (for
example, one containing the offset of another component). An
implementation may generate names that denote such implementation-defined
components; such names shall be implementation-defined
attribute_references. An implementation may allow such
implementation-defined names to be used in record_
representation_clauses. An implementation can restrict such
component_clauses in any manner it sees fit.
16. If a record_representation_clause is given for an untagged derived type,
the storage place attributes for all of the components of the derived
type may differ from those of the corresponding components of the parent
type, even for components whose storage place is not specified explicitly
in the record_representation_clause.
Implementation Advice
17. The recommended level of support for record_representation_clauses is:
a. An implementation should support storage places that can be
extracted with a load, mask, shift sequence of machine code, and set
with a load, shift, mask, store sequence, given the available
machine instructions and run-time model.
b. A storage place should be supported if its size is equal to the Size
of the component subtype, and it starts and ends on a boundary that
obeys the Alignment of the component subtype.
c. If the default bit ordering applies to the declaration of a given
type, then for a component whose subtype's Size is less than the
word size, any storage place that does not cross an aligned word
boundary should be supported.
d. An implementation may reserve a storage place for the tag field of a
tagged type, and disallow other components from overlapping that
place.
e. An implementation need not support a component_clause for a
component of an extension part if the storage place is not after the
storage places of all components of the parent type, whether or not
those storage places had been specified.
NOTES
1. (12) If no component_clause is given for a component, then the choice of
the storage place for the component is left to the implementation. If
component_clauses are given for all components, the
record_representation_clause completely specifies the representation of
the type and will be obeyed exactly by the implementation.
Examples
2. Example of specifying the layout of a record type:
3.
Word : constant := 4; -- storage element is byte, 4 bytes per word
4.
type State is (A,M,W,P);
type Mode is (Fix, Dec, Exp, Signif);
5.
type Byte_Mask is array (0┬╖┬╖7) of Boolean;
type State_Mask is array (State) of Boolean;
type Mode_Mask is array (Mode) of Boolean;
6.
type Program_Status_Word is
record
System_Mask : Byte_Mask;
Protection_Key : Integer range 0 ┬╖┬╖ 3;
Machine_State : State_Mask;
Interrupt_Cause : Interruption_Code;
Ilc : Integer range 0 ┬╖┬╖ 3;
Cc : Integer range 0 ┬╖┬╖ 3;
Program_Mask : Mode_Mask;
Inst_Address : Address;
end record;
7.
for Program_Status_Word use
record
System_Mask at 0*Word range 0 ┬╖┬╖ 7;
Protection_Key at 0*Word range 10 ┬╖┬╖ 11; -- bits 8,9 unused
Machine_State at 0*Word range 12 ┬╖┬╖ 15;
Interrupt_Cause at 0*Word range 16 ┬╖┬╖ 31;
Ilc at 1*Word range 0 ┬╖┬╖ 1; -- second word
Cc at 1*Word range 2 ┬╖┬╖ 3;
Program_Mask at 1*Word range 4 ┬╖┬╖ 7;
Inst_Address at 1*Word range 8 ┬╖┬╖ 31;
end record;
8.
for Program_Status_Word'Size use 8*System.Storage_Unit;
for Program_Status_Word'Alignment use 8;
NOTES
9. (13) Note on the example: The record_representation_clause defines the
record layout. The Size clause guarantees that (at least) eight storage
elements are used for objects of the type. The Alignment clause
guarantees that aliased, imported, or exported objects of the type will
have addresses divisible by eight.
ΓòÉΓòÉΓòÉ 16.5.2. Storage Place Attributes ΓòÉΓòÉΓòÉ
Static Semantics
1. For a component C of a composite, non-array object R, the storage place
attributes are defined:
2. R.C'Position
Denotes the same value as R.C'Address - R'Address. The value
of this attribute is of the type universal_integer.
3. R.C'First_Bit
Denotes the offset, from the start of the first of the
storage elements occupied by C, of the first bit occupied by
C. This offset is measured in bits. The first bit of a
storage element is numbered zero. The value of this
attribute is of the type universal_integer.
4. R.C'Last_Bit
Denotes the offset, from the start of the first of the
storage elements occupied by C, of the last bit occupied by
C. This offset is measured in bits. The value of this
attribute is of the type universal_integer.
Implementation Advice
5. If a component is represented using some form of pointer (such as an
offset) to the actual data of the component, and this data is contiguous
with the rest of the object, then the storage place attributes should
reflect the place of the actual data, not the pointer. If a component is
allocated discontiguously from the rest of the object, then a warning
should be generated upon reference to one of its storage place
attributes.
ΓòÉΓòÉΓòÉ 16.5.3. Bit Ordering ΓòÉΓòÉΓòÉ
1. The Bit_Order attribute specifies the interpretation of the storage place
attributes.
Static Semantics
2. A bit ordering is a method of interpreting the meaning of the storage
place attributes. High_Order_First (known in the vernacular as ``big
endian'') means that the first bit of a storage element (bit 0) is the
most significant bit (interpreting the sequence of bits that represent a
component as an unsigned integer value). Low_Order_First (known in the
vernacular as ``little endian'') means the opposite: the first bit is the
least significant.
3. For every specific record subtype S, the following attribute is defined:
4. S'Bit_Order
Denotes the bit ordering for the type of S. The value of this
attribute is of type System.Bit_Order. Bit_Order may be
specified for specific record types via an
attribute_definition_clause; the expression of such a
clause shall be static.
5. If Word_Size = Storage_Unit, the default bit ordering is implementation
defined. If Word_Size > Storage_Unit, the default bit ordering is the
same as the ordering of storage elements in a word, when interpreted as
an integer.
6. The storage place attributes of a component of a type are interpreted
according to the bit ordering of the type.
Implementation Advice
7. The recommended level of support for the nondefault bit ordering is:
a. If Word_Size = Storage_Unit, then the implementation should support
the nondefault bit ordering in addition to the default bit ordering.
ΓòÉΓòÉΓòÉ 16.6. Change of Representation ΓòÉΓòÉΓòÉ
1. A type_conversion, see 4.6 can be used to convert between two different
representations of the same array or record. To convert an array from one
representation to another, two array types need to be declared with
matching component subtypes, and convertible index types. If one type has
packing specified and the other does not, then explicit conversion can be
used to pack or unpack an array.
2. To convert a record from one representation to another, two record types
with a common ancestor type need to be declared, with no inherited
subprograms. Distinct representations can then be specified for the
record types, and explicit conversion between the types can be used to
effect a change in representation.
Examples
3. Example of change of representation:
4.
-- Packed_Descriptor and Descriptor are two different types
-- with identical characteristics, apart from their
-- representation
5.
type Descriptor is
record
-- components of a descriptor
end record;
6.
type Packed_Descriptor is new Descriptor;
7.
for Packed_Descriptor use
record
-- component clauses for some or for all components
end record;
8.
-- Change of representation can now be accomplished
-- by explicit type conversions:
9.
D : Descriptor;
P : Packed_Descriptor;
10.
P := Packed_Descriptor(D); -- pack D
D := Descriptor(P); -- unpack P
ΓòÉΓòÉΓòÉ 16.7. The Package System ΓòÉΓòÉΓòÉ
1. For each implementation there is a library package called System which
includes the definitions of certain configuration-dependent
characteristics.
Static Semantics
2. The following language-defined library package exists:
3.
package System is
pragma Preelaborate(System);
4.
type Name is implementation-defined-enumeration-type;
System_Name : constant Name := implementation-defined;
5.
-- System-Dependent Named Numbers:
6.
Min_Int : constant := root_integer'First;
Max_Int : constant := root_integer'Last;
7.
Max_Binary_Modulus : constant := implementation-defined;
Max_Nonbinary_Modulus : constant := implementation-defined;
8.
Max_Base_Digits : constant := root_real'Digits;
Max_Digits : constant := implementation-defined;
9.
Max_Mantissa : constant := implementation-defined;
Fine_Delta : constant := implementation-defined;
10.
Tick : constant := implementation-defined;
11.
-- Storage-related Declarations:
12.
type Address is implementation-defined;
Null_Address : constant Address;
13.
Storage_Unit : constant := implementation-defined;
Word_Size : constant := implementation-defined * Storage_Unit;
Memory_Size : constant := implementation-defined;
14.
-- Address Comparison:
function "<" (Left, Right : Address) return Boolean;
function "<="(Left, Right : Address) return Boolean;
function ">" (Left, Right : Address) return Boolean;
function ">="(Left, Right : Address) return Boolean;
function "=" (Left, Right : Address) return Boolean;
-- function "/=" (Left, Right : Address) return Boolean;
-- "/=" is implicitly defined
pragma Convention(Intrinsic, "<");
┬╖┬╖┬╖
-- and so on for all language-defined subprograms in this package
15.
-- Other System-Dependent Declarations:
type Bit_Order is (High_Order_First, Low_Order_First);
Default_Bit_Order : constant Bit_Order;
16.
-- Priority-related declarations, see D.1.:
subtype Any_Priority is Integer
range implementation-defined;
subtype Priority is Any_Priority
range Any_Priority'First ┬╖┬╖ implementation-defined;
subtype Interrupt_Priority is Any_Priority
range Priority'Last+1 ┬╖┬╖ Any_Priority'Last;
17.
Default_Priority : constant Priority
:= (Priority'First + Priority'Last)/2;
18.
private
┬╖┬╖┬╖ -- not specified by the language
end System;
19. Name is an enumeration subtype. Values of type Name are the names of
alternative machine configurations handled by the implementation.
System_Name represents the current machine configuration.
20. The named numbers Fine_Delta and Tick are of the type universal_real; the
others are of the type universal_integer.
21. The meanings of the named numbers are:
22. Min_Int
The smallest (most negative) value allowed for the
expressions of a signed_integer_type_definition.
23. Max_Int
The largest (most positive) value allowed for the expressions
of a signed_integer_type_definition.
24. Max_Binary_Modulus
A power of two such that it, and all lesser positive powers
of two, are allowed as the modulus of a
modular_type_definition.
25. Max_Nonbinary_Modulus
A value such that it, and all lesser positive integers, are
allowed as the modulus of a modular_type_definition.
26. Max_Base_Digits
The largest value allowed for the requested decimal precision
in a floating_point_definition.
27. Max_Digits
The largest value allowed for the requested decimal precision
in a floating_point_definition that has no
real_range_specification. Max_Digits is less than or equal
to Max_Base_Digits.
28. Max_Mantissa
The largest possible number of binary digits in the mantissa
of machine numbers of a user-defined ordinary fixed point
type. (The mantissa is defined in G.)
29. Fine_Delta
The smallest delta allowed in an
ordinary_fixed_point_definition that has the
real_range_specification range -1.0 ┬╖┬╖ 1.0.
30. Tick
A period in seconds approximating the real time interval
during which the value of Calendar.Clock remains constant.
31. Storage_Unit
The number of bits per storage element.
32. Word_Size
The number of bits per word.
33. Memory_Size
An implementation-defined value that is intended to reflect
the memory size of the configuration in storage elements.
34. Address is of a definite, nonlimited type. Address represents machine
addresses capable of addressing individual storage elements. Null_Address
is an address that is distinct from the address of any object or program
unit.
35. See 13.5.3, for an explanation of Bit_Order and Default_Bit_Order.
Implementation Permissions
36. An implementation may add additional implementation-defined declarations
to package System and its children. However, it is usually better for the
implementation to provide additional functionality via
implementation-defined children of System. Package System may be declared
pure.
Implementation Advice
37. Address should be of a private type.
NOTES
38. (14) There are also some language-defined child packages of System
defined elsewhere.
13.7.1 The Package System.Storage_Elements
13.7.2 The Package System.Address_To_Access_Conversions
ΓòÉΓòÉΓòÉ 16.7.1. The Package System.Storage_Elements ΓòÉΓòÉΓòÉ
Static Semantics
1. The following language-defined library package exists:
2.
package System.Storage_Elements is
pragma Preelaborate(System.Storage_Elements);
3.
type Storage_Offset is range implementation-defined;
4.
subtype Storage_Count is Storage_Offset
range 0┬╖┬╖Storage_Offset'Last;
5.
type Storage_Element is mod implementation-defined;
for Storage_Element'Size use Storage_Unit;
type Storage_Array is array
(Storage_Offset range <>) of aliased Storage_Element;
for Storage_Array'Component_Size use Storage_Unit;
6.
-- Address Arithmetic:
7.
function "+"(Left : Address; Right : Storage_Offset)
return Address;
function "+"(Left : Storage_Offset; Right : Address)
return Address;
function "-"(Left : Address; Right : Storage_Offset)
return Address;
function "-"(Left, Right : Address)
return Storage_Offset;
8.
function "mod"(Left : Address; Right : Storage_Offset)
return Storage_Offset;
9.
-- Conversion to/from integers:
10.
type Integer_Address is implementation-defined;
function To_Address(Value : Integer_Address) return Address;
function To_Integer(Value : Address) return Integer_Address;
11.
pragma Convention(Intrinsic, "+");
-- ┬╖┬╖┬╖and so on for all language-defined subprograms
-- declared in this package.
end System.Storage_Elements;
12. Storage_Element represents a storage element. Storage_Offset represents
an offset in storage elements. Storage_Count represents a number of
storage elements. Storage_Array represents a contiguous sequence of
storage elements.
13. Integer_Address is a (signed or modular) integer subtype. To_Address and
To_Integer convert back and forth between this type and Address.
Implementation Requirements
14. Storage_Offset'Last shall be greater than or equal to Integer'Last or the
largest possible storage offset, whichever is smaller.
Storage_Offset'First shall be <= (-Storage_Offset'Last).
Implementation Permissions
15. Package System.Storage_Elements may be declared pure.
Implementation Advice
16. Operations in System and its children should reflect the target
environment semantics as closely as is reasonable. For example, on most
machines, it makes sense for address arithmetic to ``wrap around.''
Operations that do not make sense should raise Program_Error.
ΓòÉΓòÉΓòÉ 16.7.2. The Package System.Address_To_Access_Conversions ΓòÉΓòÉΓòÉ
Static Semantics
1. The following language-defined generic library package exists:
2.
generic
type Object(<>) is limited private;
package System.Address_To_Access_Conversions is
pragma Preelaborate(Address_To_Access_Conversions);
3.
type Object_Pointer is access all Object;
function To_Pointer(Value : Address) return Object_Pointer;
function To_Address(Value : Object_Pointer) return Address;
4.
pragma Convention(Intrinsic, To_Pointer);
pragma Convention(Intrinsic, To_Address);
end System.Address_To_Access_Conversions;
5. The To_Pointer and To_Address subprograms convert back and forth between
values of types Object_Pointer and Address. To_Pointer(X'Address) is
equal to X'Unchecked_Access for any X that allows Unchecked_Access.
To_Pointer(Null_Address) returns null. For other addresses, the behavior
is unspecified. To_Address(null) returns Null_Address (for null of the
appropriate type). To_Address(Y), where Y /= null, returns Y.all'Address.
Implementation Permissions
6. An implementation may place restrictions on instantiations of
Address_To_Access_Conversions.
ΓòÉΓòÉΓòÉ 16.8. Machine Code Insertions ΓòÉΓòÉΓòÉ
1. A machine code insertion can be achieved by a call to a subprogram whose
sequence_of_statements contains code_statements.
Syntax
2.
code_statement ::= qualified_expression;
a. A code_statement is only allowed in the
handled_sequence_of_statements of a subprogram_body. If a
subprogram_body contains any code_statements, then within this
subprogram_body the only allowed form of statement is a
code_statement (labeled or not), the only allowed declarative_items
are use_clauses, and no exception_handler is allowed (comments and
pragmas are allowed as usual).
Name Resolution Rules
1. The qualified_expression is expected to be of any type.
Legality Rules
2. The qualified_expression shall be of a type declared in package
System.Machine_Code.
3. A code_statement shall appear only within the scope of a with_clause that
mentions package System.Machine_Code.
Static Semantics
4. The contents of the library package System.Machine_Code (if provided) are
implementation defined. The meaning of code_statements is implementation
defined. Typically, each qualified_expression represents a machine
instruction or assembly directive.
Implementation Permissions
5. An implementation may place restrictions on code_statements. An
implementation is not required to provide package System.Machine_Code.
NOTES
6. (15) An implementation may provide implementation-defined pragmas
specifying register conventions and calling conventions.
7. (16) Machine code functions are exempt from the rule that a
return_statement is required. In fact, return_statements are forbidden,
since only code_statements are allowed.
8. (17) Intrinsic subprograms, see 6.3.1: ``Conformance Rules'', can also be
used to achieve machine code insertions. Interface to assembly language
can be achieved using the features in Annex B, see B: ``Interface to
Other Languages''.
Examples
9. Example of a code statement:
10.
M : Mask;
procedure Set_Mask; pragma Inline(Set_Mask);
11.
procedure Set_Mask is
use System.Machine_Code;
-- assume ``with System.Machine_Code;'' appears somewhere above
begin
SI_Format'(Code => SSM, B => M'Base_Reg, D => M'Disp);
-- Base_Reg and Disp are implementation-defined attributes
end Set_Mask;
ΓòÉΓòÉΓòÉ 16.9. Unchecked Type Conversions ΓòÉΓòÉΓòÉ
1. An unchecked type conversion can be achieved by a call to an instance of
the generic function Unchecked_Conversion.
Static Semantics
2. The following language-defined generic library function exists:
3.
generic
type Source(<>) is limited private;
type Target(<>) is limited private;
function Ada.Unchecked_Conversion(S : Source) return Target;
pragma Convention(Intrinsic, Ada.Unchecked_Conversion);
pragma Pure(Ada.Unchecked_Conversion);
Dynamic Semantics
4. The size of the formal parameter S in an instance of Unchecked_Conversion
is that of its subtype. This is the actual subtype passed to Source,
except when the actual is an unconstrained composite subtype, in which
case the subtype is constrained by the bounds or discriminants of the
value of the actual expression passed to S.
5. If all of the following are true, the effect of an unchecked conversion
is to return the value of an object of the target subtype whose
representation is the same as that of the source object S:
a. S'Size = Target'Size.
b. S'Alignment = Target'Alignment.
c. The target subtype is not an unconstrained composite subtype.
d. S and the target subtype both have a contiguous representation.
e. The representation of S is a representation of an object of the
target subtype.
1. Otherwise, the effect is implementation defined; in particular, the
result can be abnormal, see 13.9.1.
Implementation Permissions
2. An implementation may return the result of an unchecked conversion by
reference, if the Source type is not a by-copy type. In this case, the
result of the unchecked conversion represents simply a different
(read-only) view of the operand of the conversion.
3. An implementation may place restrictions on Unchecked_Conversion.
Implementation Advice
4. The Size of an array object should not include its bounds; hence, the
bounds should not be part of the converted data.
5. The implementation should not generate unnecessary run-time checks to
ensure that the representation of S is a representation of the target
type. It should take advantage of the permission to return by reference
when possible. Restrictions on unchecked conversions should be avoided
unless required by the target environment.
6. The recommended level of support for unchecked conversions is: Unchecked
conversions should be supported and should be reversible in the cases
where this clause defines the result. To enable meaningful use of
unchecked conversion, a contiguous representation should be used for
elementary subtypes, for statically constrained array subtypes whose
component subtype is one of the subtypes described in this paragraph, and
for record subtypes without discriminants whose component subtypes are
described in this paragraph.
13.9.1 Data Validity
13.9.2 The Valid Attribute
ΓòÉΓòÉΓòÉ 16.9.1. Data Validity ΓòÉΓòÉΓòÉ
1. Certain actions that can potentially lead to erroneous execution are not
directly erroneous, but instead can cause objects to become abnormal.
Subsequent uses of abnormal objects can be erroneous.
2. A scalar object can have an invalid representation, which means that the
object's representation does not represent any value of the object's
subtype. The primary cause of invalid representations is uninitialized
variables.
3. Abnormal objects and invalid representations are explained in this
subclause.
Dynamic Semantics
4. When an object is first created, and any explicit or default
initializations have been performed, the object and all of its parts are
in the normal state. Subsequent operations generally leave them normal.
However, an object or part of an object can become abnormal in the
following ways:
a. An assignment to the object is disrupted due to an abort, see 9.8,
or due to the failure of a language-defined check, see 11.6.
b. The object is not scalar, and is passed to an in out or out
parameter of an imported procedure or language-defined input
procedure, if after return from the procedure the representation of
the parameter does not represent a value of the parameter's subtype.
1. Whether or not an object actually becomes abnormal in these cases is not
specified. An abnormal object becomes normal again upon successful
completion of an assignment to the object as a whole.
Erroneous Execution
2. It is erroneous to evaluate a primary that is a name denoting an abnormal
object, or to evaluate a prefix that denotes an abnormal object.
Bounded (Run-Time) Errors
3. If the representation of a scalar object does not represent a value of
the object's subtype (perhaps because the object was not initialized),
the object is said to have an invalid representation. It is a bounded
error to evaluate the value of such an object. If the error is detected,
either Constraint_Error or Program_Error is raised. Otherwise, execution
continues using the invalid representation. The rules of the language
outside this subclause assume that all objects have valid
representations. The semantics of operations on invalid representations
are as follows:
a. If the representation of the object represents a value of the
object's type, the value of the type is used.
b. If the representation of the object does not represent a value of
the object's type, the semantics of operations on such
representations is implementation-defined, but does not by itself
lead to erroneous or unpredictable execution, or to other objects
becoming abnormal.
Erroneous Execution
1. A call to an imported function or an instance of Unchecked_Conversion is
erroneous if the result is scalar, and the result object has an invalid
representation.
2. The dereference of an access value is erroneous if it does not designate
an object of an appropriate type or a subprogram with an appropriate
profile, if it designates a nonexistent object, or if it is an
access-to-variable value that designates a constant object. Such an
access value can exist, for example, because of Unchecked_Deallocation,
Unchecked_Access, or Unchecked_Conversion.
NOTES
3. (18) Objects can become abnormal due to other kinds of actions that
directly update the object's representation; such actions are generally
considered directly erroneous, however.
ΓòÉΓòÉΓòÉ 16.9.2. The Valid Attribute ΓòÉΓòÉΓòÉ
1. The Valid attribute can be used to check the validity of data produced by
unchecked conversion, input, interface to foreign languages, and the
like.
Static Semantics
2. For a prefix X that denotes a scalar object (after any implicit
dereference), the following attribute is defined:
3. X'Valid
Yields True if and only if the object denoted by X is normal
and has a valid representation. The value of this attribute
is of the predefined type Boolean.
NOTES
4. (19) Invalid data can be created in the following cases (not counting
erroneous or unpredictable execution):
a. an uninitialized scalar object,
b. the result of an unchecked conversion,
c. input,
d. interface to another language (including machine code),
e. aborting an assignment,
f. disrupting an assignment due to the failure of a language-defined
check (see 11.6) and
g. use of an object whose Address has been specified.
1. (20) X'Valid is not considered to be a read of X; hence, it is not an
error to check the validity of invalid data.
ΓòÉΓòÉΓòÉ 16.10. Unchecked Access Value Creation ΓòÉΓòÉΓòÉ
1. The attribute Unchecked_Access is used to create access values in an
unsafe manner -- the programmer is responsible for preventing ``dangling
references.''
Static Semantics
2. The following attribute is defined for a prefix X that denotes an aliased
view of an object:
3. X'Unchecked_Access
All rules and semantics that apply to X'Access, see 3.10.2,
apply also to X'Unchecked_Access, except that, for the
purposes of accessibility rules and checks, it is as if X
were declared immediately within a library package.
NOTES
4. (21) This attribute is provided to support the situation where a local
object is to be inserted into a global linked data structure, when the
programmer knows that it will always be removed from the data structure
prior to exiting the object's scope. The Access attribute would be
illegal in this case, see 3.10.2: ``Operations of Access Types''.
5. (22) There is no Unchecked_Access attribute for subprograms.
ΓòÉΓòÉΓòÉ 16.11. Storage Management ΓòÉΓòÉΓòÉ
1. Each access-to-object type has an associated storage pool. The storage
allocated by an allocator comes from the pool; instances of
Unchecked_Deallocation return storage to the pool. Several access types
can share the same pool.
2. A storage pool is a variable of a type in the class rooted at
Root_Storage_Pool, which is an abstract limited controlled type. By
default, the implementation chooses a standard storage pool for each
access type. The user may define new pool types, and may override the
choice of pool for an access type by specifying Storage_Pool for the
type.
Legality Rules
3. If Storage_Pool is specified for a given access type, Storage_Size shall
not be specified for it.
Static Semantics
4. The following language-defined library package exists:
5.
with Ada.Finalization;
with System.Storage_Elements;
package System.Storage_Pools is
pragma Preelaborate(System.Storage_Pools);
6.
type Root_Storage_Pool is
abstract new
Ada.Finalization.Limited_Controlled with private;
7.
procedure Allocate(
Pool : in out Root_Storage_Pool;
Storage_Address : out Address;
Size_In_Storage_Elements : in Storage_Elements.Storage_Count;
Alignment : in Storage_Elements.Storage_Count) is abstract;
8.
procedure Deallocate(
Pool : in out Root_Storage_Pool;
Storage_Address : in Address;
Size_In_Storage_Elements : in Storage_Elements.Storage_Count;
Alignment : in Storage_Elements.Storage_Count) is abstract;
9.
function Storage_Size(Pool : Root_Storage_Pool)
return Storage_Elements.Storage_Count is abstract;
10.
private
┬╖┬╖┬╖ -- not specified by the language
end System.Storage_Pools;
11. A storage pool type (or pool type) is a descendant of Root_Storage_Pool.
The elements of a storage pool are the objects allocated in the pool by
allocators.
12. For every access subtype S, the following attributes are defined:
13. S'Storage_Pool
Denotes the storage pool of the type of S. The type of this
attribute is Root_Storage_Pool'Class.
14. S'Storage_Size
Yields the result of calling Storage_Size(S'Storage_Pool),
which is intended to be a measure of the number of storage
elements reserved for the pool. The type of this attribute
is universal_integer.
15. Storage_Size or Storage_Pool may be specified for a non-derived
access-to-object type via an attribute_definition_clause; the name in a
Storage_Pool clause shall denote a variable.
16. An allocator of type T allocates storage from T's storage pool. If the
storage pool is a user-defined object, then the storage is allocated by
calling Allocate, passing T'Storage_Pool as the Pool parameter. The
Size_In_Storage_Elements parameter indicates the number of storage
elements to be allocated, and is no more than
D'Max_Size_In_Storage_Elements, where D is the designated subtype. The
Alignment parameter is D'Alignment. The result returned in the
Storage_Address parameter is used by the allocator as the address of the
allocated storage, which is a contiguous block of memory of
Size_In_Storage_Elements storage elements. Any exception propagated by
Allocate is propagated by the allocator.
17. If Storage_Pool is not specified for a type defined by an
access_to_object_definition, then the implementation chooses a standard
storage pool for it in an implementation-defined manner. In this case,
the exception Storage_Error is raised by an allocator if there is not
enough storage. It is implementation defined whether or not the
implementation provides user-accessible names for the standard pool
type(s).
18. If Storage_Size is specified for an access type, then the Storage_Size of
this pool is at least that requested, and the storage for the pool is
reclaimed when the master containing the declaration of the access type
is left. If the implementation cannot satisfy the request, Storage_Error
is raised at the point of the attribute_definition_clause. If neither
Storage_Pool nor Storage_Size are specified, then the meaning of
Storage_Size is implementation defined.
19. If Storage_Pool is specified for an access type, then the specified pool
is used.
20. The effect of calling Allocate and Deallocate for a standard storage pool
directly (rather than implicitly via an allocator or an instance of
Unchecked_Deallocation) is unspecified.
Erroneous Execution
21. If Storage_Pool is specified for an access type, then if Allocate can
satisfy the request, it should allocate a contiguous block of memory, and
return the address of the first storage element in Storage_Address. The
block should contain Size_In_Storage_Elements storage elements, and
should be aligned according to Alignment. The allocated storage should
not be used for any other purpose while the pool element remains in
existence. If the request cannot be satisfied, then Allocate should
propagate an exception (such as Storage_Error). If Allocate behaves in
any other manner, then the program execution is erroneous.
Documentation Requirements
22. An implementation shall document the set of values that a user-defined
Allocate procedure needs to accept for the Alignment parameter. An
implementation shall document how the standard storage pool is chosen,
and how storage is allocated by standard storage pools.
Implementation Advice
23. An implementation should document any cases in which it dynamically
allocates heap storage for a purpose other than the evaluation of an
allocator.
24. A default (implementation-provided) storage pool for an
access-to-constant type should not have overhead to support deallocation
of individual objects.
25. A storage pool for an anonymous access type should be created at the
point of an allocator for the type, and be reclaimed when the designated
object becomes inaccessible.
NOTES
26. (23) A user-defined storage pool type can be obtained by extending the
Root_Storage_Pool type, and overriding the primitive subprograms
Allocate, Deallocate, and Storage_Size. A user-defined storage pool can
then be obtained by declaring an object of the type extension. The user
can override Initialize and Finalize if there is any need for non-trivial
initialization and finalization for a user-defined pool type. For
example, Finalize might reclaim blocks of storage that are allocated
separately from the pool object itself.
27. (24) The writer of the user-defined allocation and deallocation
procedures, and users of allocators for the associated access type, are
responsible for dealing with any interactions with tasking. In
particular:
a. If the allocators are used in different tasks, they require mutual
exclusion.
b. If they are used inside protected objects, they cannot block.
c. If they are used by interrupt handlers, see C.3: ``Interrupt
Support'', the mutual exclusion mechanism has to work properly in
that context.
1. (25) The primitives Allocate, Deallocate, and Storage_Size are declared
as abstract, see 3.9.3, and therefore they have to be overridden when a
new (non-abstract) storage pool type is declared.
Examples
2. To associate an access type with a storage pool object, the user first
declares a pool object of some type derived from Root_Storage_Pool. Then,
the user defines its Storage_Pool attribute, as follows:
3.
Pool_Object : Some_Storage_Pool_Type;
4.
type T is access Designated;
for T'Storage_Pool use Pool_Object;
5. Another access type may be added to an existing storage pool, via:
6.
for T2'Storage_Pool use T'Storage_Pool;
7. The semantics of this is implementation defined for a standard storage
pool.
8. As usual, a derivative of Root_Storage_Pool may define additional
operations. For example, presuming that Mark_Release_Pool_Type has two
additional operations, Mark and Release, the following is a possible use:
9.
type Mark_Release_Pool_Type
(Pool_Size : Storage_Elements.Storage_Count;
Block_Size : Storage_Elements.Storage_Count)
is new Root_Storage_Pool with limited private;
10.
┬╖┬╖┬╖
11.
MR_Pool : Mark_Release_Pool_Type (Pool_Size => 2000,
Block_Size => 100);
12.
type Acc is access ┬╖┬╖┬╖;
for Acc'Storage_Pool use MR_Pool;
┬╖┬╖┬╖
13.
Mark(MR_Pool);
┬╖┬╖┬╖ -- Allocate objects using ``new Designated(┬╖┬╖┬╖)''.
Release(MR_Pool); -- Reclaim the storage.
13.11.1 The Max_Size_In_Storage_Elements Attribute
13.11.2 Unchecked Storage Deallocation
13.11.3 Pragma Controlled
ΓòÉΓòÉΓòÉ 16.11.1. The Max_Size_In_Storage_Elements Attribute ΓòÉΓòÉΓòÉ
1. The Max_Size_In_Storage_Elements attribute is useful in writing
user-defined pool types.
Static Semantics
2. For every subtype S, the following attribute is defined:
3. S'Max_Size_In_Storage_Elements
4.
Denotes the maximum value for Size_In_Storage_Elements that
will be requested via Allocate for an access type whose
designated subtype is S. The value of this attribute is of
type universal_integer.
ΓòÉΓòÉΓòÉ 16.11.2. Unchecked Storage Deallocation ΓòÉΓòÉΓòÉ
1. Unchecked storage deallocation of an object designated by a value of an
access type is achieved by a call to an instance of the generic procedure
Unchecked_Deallocation.
Static Semantics
2. The following language-defined generic library procedure exists:
3.
generic
type Object(<>) is limited private;
type Name is access Object;
procedure Ada.Unchecked_Deallocation(X : in out Name);
pragma Convention(Intrinsic, Ada.Unchecked_Deallocation);
pragma Preelaborate(Ada.Unchecked_Deallocation);
Dynamic Semantics
4. Given an instance of Unchecked_Deallocation declared as follows:
5.
procedure Free is
new Ada.Unchecked_Deallocation
(object_subtype_name, access_to_variable_subtype_name);
6. Procedure Free has the following effect:
a. After executing Free(X), the value of X is null.
b. Free(X), when X is already equal to null, has no effect.
c. Free(X), when X is not equal to null first performs finalization, as
described in 7.6. It then deallocates the storage occupied by the
object designated by X. If the storage pool is a user-defined
object, then the storage is deallocated by calling Deallocate,
passing access_to_variable_subtype_name'Storage_Pool as the Pool
parameter. Storage_Address is the value returned in the
Storage_Address parameter of the corresponding Allocate call.
Size_In_Storage_Elements and Alignment are the same values passed to
the corresponding Allocate call. There is one exception: if the
object being freed contains tasks, the object might not be
deallocated.
1. After Free(X), the object designated by X, and any subcomponents thereof,
no longer exist; their storage can be reused for other purposes.
Bounded (Run-Time) Errors
2. It is a bounded error to free a discriminated, unterminated task object.
The possible consequences are:
a. No exception is raised.
b. Program_Error or Tasking_Error is raised at the point of the
deallocation.
c. Program_Error or Tasking_Error is raised in the task the next time
it references any of the discriminants.
1. In the first two cases, the storage for the discriminants (and for any
enclosing object if it is designated by an access discriminant of the
task) is not reclaimed prior to task termination.
Erroneous Execution
2. Evaluating a name that denotes a nonexistent object is erroneous. The
execution of a call to an instance of Unchecked_Deallocation is erroneous
if the object was created other than by an allocator for an access type
whose pool is Name'Storage_Pool.
Implementation Advice
3. For a standard storage pool, Free should actually reclaim the storage.
NOTES
4. (26) The rules here that refer to Free apply to any instance of
Unchecked_Deallocation.
5. (27) Unchecked_Deallocation cannot be instantiated for an
access-to-constant type. This is implied by the rules of 12.5.4.
ΓòÉΓòÉΓòÉ 16.11.3. Pragma Controlled ΓòÉΓòÉΓòÉ
1. Pragma Controlled is used to prevent any automatic reclamation of storage
(garbage collection) for the objects created by allocators of a given
access type.
Syntax
2. The form of a pragma Controlled is as follows:
3.
pragma Controlled(first_subtype_local_name);
Legality Rules
4. The first_subtype_local_name of a pragma Controlled shall denote a
non-derived access subtype.
Static Semantics
5. A pragma Controlled is a representation pragma that specifies the
controlled aspect of representation.
6. Garbage collection is a process that automatically reclaims storage, or
moves objects to a different address, while the objects still exist.
7. If a pragma Controlled is specified for an access type with a standard
storage pool, then garbage collection is not performed for objects in
that pool.
Implementation Permissions
8. An implementation need not support garbage collection, in which case, a
pragma Controlled has no effect.
ΓòÉΓòÉΓòÉ 16.12. Pragma Restrictions ΓòÉΓòÉΓòÉ
1. A pragma Restrictions expresses the user's intent to abide by certain
restrictions. This may facilitate the construction of simpler run-time
environments.
Syntax
2. The form of a pragma Restrictions is as follows:
3.
pragma Restrictions(restriction{, restriction});
4.
restriction ::= restriction_identifier
| restriction_parameter_identifier => expression
Name Resolution Rules
5. Unless otherwise specified for a particular restriction, the expression
is expected to be of any integer type.
Legality Rules
6. Unless otherwise specified for a particular restriction, the expression
shall be static, and its value shall be nonnegative.
Static Semantics
7. The set of restrictions is implementation defined.
Post-Compilation Rules
8. A pragma Restrictions is a configuration pragma; unless otherwise
specified for a particular restriction, a partition shall obey the
restriction if a pragma Restrictions applies to any compilation unit
included in the partition.
Implementation Permissions
9. An implementation may place limitations on the values of the expression
that are supported, and limitations on the supported combinations of
restrictions. The consequences of violating such limitations are
implementation defined.
NOTES
10. (28) Restrictions intended to facilitate the construction of efficient
tasking run-time systems are defined in D.7. Safety- and security-related
restrictions are defined in H.4.
11. (29) An implementation has to enforce the restrictions in cases where
enforcement is required, even if it chooses not to take advantage of the
restrictions in terms of efficiency.
ΓòÉΓòÉΓòÉ 16.13. Streams ΓòÉΓòÉΓòÉ
1. A stream is a sequence of elements comprising values from possibly
different types and allowing sequential access to these values. A stream
type is a type in the class whose root type is Streams.Root_Stream_Type.
A stream type may be implemented in various ways, such as an external
sequential file, an internal buffer, or a network channel.
13.13.1 The Package Streams
13.13.2 Stream-Oriented Attributes
ΓòÉΓòÉΓòÉ 16.13.1. The Package Streams ΓòÉΓòÉΓòÉ
Static Semantics
1. The abstract type Root_Stream_Type is the root type of the class of
stream types. The types in this class represent different kinds of
streams. A new stream type is defined by extending the root type (or some
other stream type), overriding the Read and Write operations, and
optionally defining additional primitive subprograms, according to the
requirements of the particular kind of stream. The predefined
stream-oriented attributes like T'Read and T'Write make dispatching calls
on the Read and Write procedures of the Root_Stream_Type. (User-defined
T'Read and T'Write attributes can also make such calls, or can call the
Read and Write attributes of other types.)
2.
package Ada.Streams is
pragma Pure(Streams);
3.
type Root_Stream_Type is abstract tagged limited private;
4.
type Stream_Element is mod implementation-defined;
type Stream_Element_Offset is range implementation-defined;
subtype Stream_Element_Count is
Stream_Element_Offset range 0┬╖┬╖Stream_Element_Offset'Last;
type Stream_Element_Array is
array(Stream_Element_Offset range <>) of Stream_Element;
5.
procedure Read(
Stream : in out Root_Stream_Type;
Item : out Stream_Element_Array;
Last : out Stream_Element_Offset) is abstract;
6.
procedure Write(
Stream : in out Root_Stream_Type;
Item : in Stream_Element_Array) is abstract;
7.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Streams;
8. The Read operation transfers Item'Length stream elements from the
specified stream to fill the array Item. The index of the last stream
element transferred is returned in Last. Last is less than Item'Last only
if the end of the stream is reached.
9. The Write operation appends Item to the specified stream.
NOTES
10. (30) See A.12.1: ``The Package Streams.Stream_IO'', for an example of
extending type Root_Stream_Type.
ΓòÉΓòÉΓòÉ 16.13.2. Stream-Oriented Attributes ΓòÉΓòÉΓòÉ
1. The Write, Read, Output, and Input attributes convert values to a stream
of elements and reconstruct values from a stream.
Static Semantics
2. For every subtype S of a specific type T, the following attributes are
defined.
3. S'Write
S'Write denotes a procedure with the following specification:
a.
procedure S'Write(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T)
b. S'Write writes the value of Item to Stream.
1. S'Read
S'Read denotes a procedure with the following specification:
a.
procedure S'Read(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : out T)
b. S'Read reads the value of Item from Stream.
1. For elementary types, the representation in terms of stream elements is
implementation defined. For composite types, the Write or Read attribute
for each component is called in a canonical order. The canonical order of
components is last dimension varying fastest for an array, and positional
aggregate order for a record. Bounds are not included in the stream if T
is an array type. If T is a discriminated type, discriminants are
included only if they have defaults. If T is a tagged type, the tag is
not included.
2. For every subtype S'Class of a class-wide type T'Class:
3. S'Class'Write
S'Class'Write denotes a procedure with the following
specification:
a.
procedure S'Class'Write(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T'Class)
b. Dispatches to the subprogram denoted by the Write attribute of the
specific type identified by the tag of Item.
1. S'Class'Read
S'Class'Read denotes a procedure with the following
specification:
a.
procedure S'Class'Read(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : out T'Class)
b. Dispatches to the subprogram denoted by the Read attribute of the
specific type identified by the tag of Item.
Implementation Advice
1. If a stream element is the same size as a storage element, then the
normal in-memory representation should be used by Read and Write for
scalar objects. Otherwise, Read and Write should use the smallest number
of stream elements needed to represent all values in the base range of
the scalar type.
Static Semantics
2. For every subtype S of a specific type T, the following attributes are
defined.
3. S'Output
S'Output denotes a procedure with the following specification:
a.
procedure S'Output(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T)
b. S'Output writes the value of Item to Stream, including any bounds or
discriminants.
1. S'Input
S'Input denotes a function with the following specification:
a.
function S'Input(
Stream : access Ada.Streams.Root_Stream_Type'Class)
return T
b. S'Input reads and returns one value from Stream, using any bounds or
discriminants written by a corresponding S'Output to determine how
much to read.
1. Unless overridden by an attribute_definition_clause, these subprograms
execute as follows:
a. If T is an array type, S'Output first writes the bounds, and S'Input
first reads the bounds. If T has discriminants without defaults,
S'Output first writes the discriminants (using S'Write for each),
and S'Input first reads the discriminants (using S'Read for each).
b. S'Output then calls S'Write to write the value of Item to the
stream. S'Input then creates an object (with the bounds or
discriminants, if any, taken from the stream), initializes it with
S'Read, and returns the value of the object.
1. For every subtype S'Class of a class-wide type T'Class:
2. S'Class'Output
S'Class'Output denotes a procedure with the following
specification:
a.
procedure S'Class'Output(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T'Class)
b. First writes the external tag of Item to Stream (by calling
String'Output(Tags.External_Tag(Item'Tag) -- see 3.9.) and then
dispatches to the subprogram denoted by the Output attribute of the
specific type identified by the tag.
1. S'Class'Input
S'Class'Input denotes a function with the following
specification:
a.
function S'Class'Input(
Stream : access Ada.Streams.Root_Stream_Type'Class)
return T'Class
b. First reads the external tag from Stream and determines the
corresponding internal tag (by calling
Tags.Internal_Tag(String'Input(Stream)) -- see 3.9.) and then
dispatches to the subprogram denoted by the Input attribute of the
specific type identified by the internal tag; returns that result.
1. In the default implementation of Read and Input for a composite type, for
each scalar component that is a discriminant or whose
component_declaration includes a default_expression, a check is made that
the value returned by Read for the component belongs to its subtype.
Constraint_Error is raised if this check fails. For other scalar
components, no check is made. For each component that is of an access
type, if the implementation can detect that the value returned by Read
for the component is not a value of its subtype, Constraint_Error is
raised. If the value is not a value of its subtype and this error is not
detected, the component has an abnormal value, and erroneous execution
can result, see 13.9.1.
2. The stream-oriented attributes may be specified for any type via an
attribute_definition_clause. All nonlimited types have default
implementations for these operations. An attribute_reference for one of
these attributes is illegal if the type is limited, unless the attribute
has been specified by an attribute_definition_clause. For an
attribute_definition_clause specifying one of these attributes, the
subtype of the Item parameter shall be the base subtype if scalar, and
the first subtype otherwise. The same rule applies to the result of the
Input function.
NOTES
3. (31) For a definite subtype S of a type T, only T'Write and T'Read are
needed to pass an arbitrary value of the subtype through a stream. For an
indefinite subtype S of a type T, T'Output and T'Input will normally be
needed, since T'Write and T'Read do not pass bounds, discriminants, or
tags.
4. (32) User-specified attributes of S'Class are not inherited by other
class-wide types descended from S.
Examples
5. Example of user-defined Write attribute:
6.
procedure My_Write
(Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : My_Integer'Base);
for My_Integer'Write use My_Write;
ΓòÉΓòÉΓòÉ 16.14. Freezing Rules ΓòÉΓòÉΓòÉ
1. This clause defines a place in the program text where each declared
entity becomes ``frozen.'' A use of an entity, such as a reference to it
by name, or (for a type) an expression of the type, causes freezing of
the entity in some contexts, as described below. The Legality Rules
forbid certain kinds of uses of an entity in the region of text where it
is frozen.
2. The freezing of an entity occurs at one or more places (freezing points)
in the program text where the representation for the entity has to be
fully determined. Each entity is frozen from its first freezing point to
the end of the program text (given the ordering of compilation units
defined in 10.1.4.
3. The end of a declarative_part, protected_body, or a declaration of a
library package or generic library package, causes freezing of each
entity declared within it, except for incomplete types. A noninstance
body causes freezing of each entity declared before it within the same
declarative_part.
4. A construct that (explicitly or implicitly) references an entity can
cause the freezing of the entity, as defined by subsequent paragraphs. At
the place where a construct causes freezing, each name, expression, or
range within the construct causes freezing:
a. The occurrence of a generic_instantiation causes freezing; also, if
a parameter of the instantiation is defaulted, the
default_expression or default_name for that parameter causes
freezing.
b. The occurrence of an object_declaration that has no corresponding
completion causes freezing.
c. The declaration of a record extension causes freezing of the parent
subtype.
1. A static expression causes freezing where it occurs. A nonstatic
expression causes freezing where it occurs, unless the expression is part
of a default_expression, a default_name, or a per-object expression of a
component's constraint, in which case, the freezing occurs later as part
of another construct.
2. The following rules define which entities are frozen at the place where a
construct causes freezing:
a. At the place where an expression causes freezing, the type of the
expression is frozen, unless the expression is an enumeration
literal used as a discrete_choice of the array_aggregate of an
enumeration_representation_clause.
b. At the place where a name causes freezing, the entity denoted by the
name is frozen, unless the name is a prefix of an expanded name; at
the place where an object name causes freezing, the nominal subtype
associated with the name is frozen.
c. At the place where a range causes freezing, the type of the range is
frozen.
d. At the place where an allocator causes freezing, the designated
subtype of its type is frozen. If the type of the allocator is a
derived type, then all ancestor types are also frozen.
e. At the place where a callable entity is frozen, each subtype of its
profile is frozen. If the callable entity is a member of an entry
family, the index subtype of the family is frozen. At the place
where a function call causes freezing, if a parameter of the call is
defaulted, the default_expression for that parameter causes
freezing.
f. At the place where a subtype is frozen, its type is frozen. At the
place where a type is frozen, any expressions or names within the
full type definition cause freezing; the first subtype, and any
component subtypes, index subtypes, and parent subtype of the type
are frozen as well. For a specific tagged type, the corresponding
class-wide type is frozen as well. For a class-wide type, the
corresponding specific type is frozen as well.
Legality Rules
1. The explicit declaration of a primitive subprogram of a tagged type shall
occur before the type is frozen, see 3.9.2.
2. A type shall be completely defined before it is frozen (see 3.11.1, and
7.3.).
3. The completion of a deferred constant declaration shall occur before the
constant is frozen, see 7.4.
4. A representation item that directly specifies an aspect of an entity
shall appear before the entity is frozen, see 13.1.
ΓòÉΓòÉΓòÉ 17. Predefined Language Environment (normative) ΓòÉΓòÉΓòÉ
1. This Annex contains the specifications of library units that shall be
provided by every implementation. There are three root library units:
Ada, Interfaces, and System; other library units are children of these:
2.
Standard -- see A.1.
Ada -- see A.2.
Asynchronous_Task_Control -- see D.11.
Calendar -- see 9.6.
Characters -- see A.3.1.
Handling -- see A.3.2.
Latin_1 -- see A.3.3.
Command_Line -- see A.15.
Decimal -- see F.2.
Direct_IO -- see A.8.4.
Dynamic_Priorities -- see D.5.
Exceptions -- see 11.4.1.
Finalization -- see 7.6.
Interrupts -- see C.3.2.
Names -- see C.3.2.
IO_Exceptions -- see A.13.
Numerics -- see A.5.
Complex_Elementary_Functions -- see G.1.2.
Complex_Types -- see G.1.1.
Discrete_Random -- see A.5.2.
Elementary_Functions -- see A.5.1.
Float_Random -- see A.5.2.
Generic_Complex_Elementary_Functions -- see G.1.2.
Generic_Complex_Types -- see G.1.1.
Generic_Elementary_Functions -- see A.5.1.
Real_Time -- see D.8.
Sequential_IO -- see A.8.1.
Storage_IO -- see A.9.
Streams -- see 13.13.1.
Stream_IO -- see A.12.1.
Strings -- see A.4.1.
Bounded -- see A.4.4.
Fixed -- see A.4.3.
Maps -- see A.4.2.
Constants -- see A.4.6.
Unbounded -- see A.4.5.
Wide_Bounded -- see A.4.7.
Wide_Fixed -- see A.4.7.
Wide_Maps -- see A.4.7.
Wide_Constants -- see A.4.7.
Wide_Unbounded -- see A.4.7.
Standard (┬╖┬╖┬╖continued)
Ada (┬╖┬╖┬╖continued)
Synchronous_Task_Control -- see D.10.
Tags -- see 3.9.
Task_Attributes -- see C.7.2.
Task_Identification -- see C.7.1.
Text_IO -- see A.10.1.
Complex_IO -- see G.1.3.
Editing -- see F.3.3.
Text_Streams -- see A.12.2.
Unchecked_Conversion -- see 13.9.
Unchecked_Deallocation -- see 13.11.2.
Wide_Text_IO -- see A.11.
Complex_IO -- see G.1.3.
Editing -- see F.3.4.
Text_Streams -- see A.12.3.
Interfaces -- see B.2.
C -- see B.3.
Pointers -- see B.3.2.
Strings -- see B.3.1.
COBOL -- see B.4.
Fortran -- see B.5.
System -- see 13.7.
Address_To_Access_Conversions -- see 13.7.2.
Machine_Code -- see 13.8.
RPC -- see E.5.
Storage_Elements -- see 13.7.1.
Storage_Pools -- see 13.11.
Implementation Requirements
3. The implementation shall ensure that each language defined subprogram is
reentrant in the sense that concurrent calls on the same subprogram
perform as specified, so long as all parameters that could be passed by
reference denote nonoverlapping objects.
Implementation Permissions
4. The implementation may restrict the replacement of language-defined
compilation units. The implementation may restrict children of
language-defined library units (other than Standard).
A.1 The Package Standard
A.2 The Package Ada
A.3 Character Handling
A.4 String Handling
A.5 The Numerics Packages
A.6 Input-Output
A.7 External Files and File Objects
A.8 Sequential and Direct Files
A.9 The Generic Package Storage_IO
A.10 Text Input-Output
A.11 Wide Text Input-Output
A.12 Stream Input-Output
A.13 Exceptions in Input-Output
A.14 File Sharing
A.15 The Package Command_Line --- The Detailed Node
Listing ---
A.1 The Package Standard
A.2 The Package Ada
A.3 Character Handling
A.3.1 The Package Characters
A.3.2 The Package Characters.Handling
A.3.3 The Package Characters.Latin_1
A.4 String Handling
A.4.1 The Package Strings
A.4.2 The Package Strings.Maps
A.4.3 Fixed-Length String Handling
A.4.4 Bounded-Length String Handling
A.4.5 Unbounded-Length String Handling
A.4.6 String-Handling Sets and Mappings
A.4.7 Wide_String Handling
A.5 The Numerics Packages
A.5.1 Elementary Functions
A.5.2 Random Number Generation
A.5.3 Attributes of Floating Point Types
A.5.4 Attributes of Fixed Point Types
A.6 Input-Output
A.7 External Files and File Objects
A.8 Sequential and Direct Files
A.8.1 The Generic Package Sequential_IO
A.8.2 File Management
A.8.3 Sequential Input-Output Operations
A.8.4 The Generic Package Direct_IO
A.8.5 Direct Input-Output Operations
A.9 The Generic Package Storage_IO
A.10 Text Input-Output
A.10.1 The Package Text_IO
A.10.2 Text File Management
A.10.3 Default Input, Output, and Error Files
A.10.4 Specification of Line and Page Lengths
A.10.5 Operations on Columns, Lines, and Pages
A.10.6 Get and Put Procedures
A.10.7 Input-Output of Characters and Strings
A.10.8 Input-Output for Integer Types
A.10.9 Input-Output for Real Types
A.10.10 Input-Output for Enumeration Types
A.11 Wide Text Input-Output
A.12 Stream Input-Output
A.12.1 The Package Streams.Stream_IO
A.12.2 The Package Text_IO.Text_Streams
A.12.3 The Package Wide_Text_IO.Text_Streams
A.13 Exceptions in Input-Output
A.14 File Sharing
A.15 The Package Command_Line
ΓòÉΓòÉΓòÉ 17.1. The Package Standard ΓòÉΓòÉΓòÉ
1. This clause outlines the specification of the package Standard containing
all predefined identifiers in the language. The corresponding package
body is not specified by the language.
2. The operators that are predefined for the types declared in the package
Standard are given in comments since they are implicitly declared.
Italics are used for pseudo-names of anonymous types (such as root_real)
and for undefined information (such as implementation-defined).
Static Semantics
3. The library package Standard has the following declaration:
4.
package Standard is
pragma Pure(Standard);
5.
type Boolean is (False, True);
6.
-- The predefined relational operators
-- for this type are as follows:
7.
-- function "=" (Left, Right : Boolean) return Boolean;
-- function "/=" (Left, Right : Boolean) return Boolean;
-- function "<" (Left, Right : Boolean) return Boolean;
-- function "<=" (Left, Right : Boolean) return Boolean;
-- function ">" (Left, Right : Boolean) return Boolean;
-- function ">=" (Left, Right : Boolean) return Boolean;
8.
-- The predefined logical operators and the predefined
-- logical negation operator are as follows:
9.
-- function "and" (Left, Right : Boolean) return Boolean;
-- function "or" (Left, Right : Boolean) return Boolean;
-- function "xor" (Left, Right : Boolean) return Boolean;
10.
-- function "not" (Right : Boolean) return Boolean;
11.
-- The integer type root_integer is predefined.
-- The corresponding universal type is universal_integer.
12.
type Integer is range implementation-defined;
13.
subtype Natural is Integer range 0 ┬╖┬╖ Integer'Last;
subtype Positive is Integer range 1 ┬╖┬╖ Integer'Last;
14.
-- The predefined operators for type Integer are as follows:
15.
-- function "=" (Left, Right : Integer'Base) return Boolean;
-- function "/=" (Left, Right : Integer'Base) return Boolean;
-- function "<" (Left, Right : Integer'Base) return Boolean;
-- function "<=" (Left, Right : Integer'Base) return Boolean;
-- function ">" (Left, Right : Integer'Base) return Boolean;
-- function ">=" (Left, Right : Integer'Base) return Boolean;
16.
-- function "+" (Right : Integer'Base) return Integer'Base;
-- function "-" (Right : Integer'Base) return Integer'Base;
-- function "abs" (Right : Integer'Base) return Integer'Base;
17.
-- function "+" (Left, Right : Integer'Base)
-- return Integer'Base;
-- function "-" (Left, Right : Integer'Base)
-- return Integer'Base;
-- function "*" (Left, Right : Integer'Base)
-- return Integer'Base;
-- function "/" (Left, Right : Integer'Base)
-- return Integer'Base;
-- function "rem" (Left, Right : Integer'Base)
-- return Integer'Base;
-- function "mod" (Left, Right : Integer'Base)
-- return Integer'Base;
18.
-- function "**"
(Left : Integer'Base;
Right : Natural) return Integer'Base;
19.
-- The specification of each operator for the type
-- root_integer, or for any additional predefined integer
-- type, is obtained by replacing Integer by the name of the type
-- in the specification of the corresponding operator of the type
-- Integer. The right operand of the exponentiation operator
-- remains as subtype Natural.
20.
-- The floating point type root_real is predefined.
-- The corresponding universal type is universal_real.
21.
type Float is digits implementation-defined;
22.
-- The predefined operators for this type are as follows:
23.
-- function "=" (Left, Right : Float) return Boolean;
-- function "/=" (Left, Right : Float) return Boolean;
-- function "<" (Left, Right : Float) return Boolean;
-- function "<=" (Left, Right : Float) return Boolean;
-- function ">" (Left, Right : Float) return Boolean;
-- function ">=" (Left, Right : Float) return Boolean;
24.
-- function "+" (Right : Float) return Float;
-- function "-" (Right : Float) return Float;
-- function "abs" (Right : Float) return Float;
25.
-- function "+" (Left, Right : Float) return Float;
-- function "-" (Left, Right : Float) return Float;
-- function "*" (Left, Right : Float) return Float;
-- function "/" (Left, Right : Float) return Float;
26.
-- function "**"
(Left : Float;
Right : Integer'Base) return Float;
27.
-- The specification of each operator for the type root_real,
-- or for any additional predefined floating point type, is
-- obtained by replacing Float by the name of the type in the
-- specification of the corresponding operator of the type Float.
28.
-- In addition, the following operators are predefined for
-- the root numeric types:
29.
function "*" (Left : root_integer; Right : root_real)
return root_real;
30.
function "*" (Left : root_real; Right : root_integer)
return root_real;
31.
function "/" (Left : root_real; Right : root_integer)
return root_real;
32.
-- The type universal_fixed is predefined.
-- The only multiplying operators defined between
-- fixed point types are
33.
function "*" (Left : universal_fixed; Right : universal_fixed)
return universal_fixed;
34.
function "/" (Left : universal_fixed; Right : universal_fixed)
return universal_fixed;
-- The declaration of type Character is based on the standard
-- ISO 8859-1 character set.
35.
-- There are no character literals corresponding to the
-- positions for control characters. They are indicated in
-- italics in this definition (see 3.5.2).
type Character is
(nul, soh, stx, etx, eot, enq, ack, bel,
bs, ht, lf, vt, ff, cr, so, si,
dle, dc1, dc2, dc3, dc4, nak, syn, etb,
can, em, sub, esc, fs, gs, rs, us,
' ', '!', '"', '#', '$', '%', '&', ''',
'(', ')', '*', '+', ',', '-', '.', '/',
'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', ':', ';', '<', '=', '>', '?',
'@', 'A', 'B', 'C', 'D', 'E', 'F', 'G',
'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
'X', 'Y', 'Z', '[', '\', ']', '^', '_',
' `', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
'p', 'q', 'r', 's', 't', 'u', 'v', 'w',
'x', 'y', 'z', '{', '|', '}', '~', del,
reserved_128, reserved_129, bph, nbh,
reserved_132, nel, ssa, esa,
hts, htj, vts, pld, plu, ri, ss2, ss3,
dcs, pu1, pu2, sts, cch, mw, spa, epa,
sos, reserved_153, sci, csi,
st, osc, pm, apc,
┬╖┬╖┬╖ );
36.
-- The predefined operators for the type Character are the
-- same as for any enumeration type.
-- The declaration of type Wide_Character is based on the
-- standard ISO 10646 BMP character set. The first 256 positions
-- have the same contents as type Character (see 3.5.2).
type Wide_Character is (nul, soh ┬╖┬╖┬╖ FFFE, FFFF);
package ASCII is ┬╖┬╖┬╖ end ASCII; --Obsolescent; (see J.5).
-- Predefined string types:
37.
type String is array(Positive range <>) of Character;
pragma Pack(String);
38.
-- The predefined operators for this type are as follows:
39.
-- function "=" (Left, Right: String) return Boolean;
-- function "/=" (Left, Right: String) return Boolean;
-- function "<" (Left, Right: String) return Boolean;
-- function "<=" (Left, Right: String) return Boolean;
-- function ">" (Left, Right: String) return Boolean;
-- function ">=" (Left, Right: String) return Boolean;
40.
-- function "&" (Left: String; Right: String)
-- return String;
-- function "&" (Left: Character; Right: String)
-- return String;
-- function "&" (Left: String; Right: Character)
-- return String;
-- function "&" (Left: Character; Right: Character)
-- return String;
41.
type Wide_String is array(Positive range <>) of Wide_Character;
pragma Pack(Wide_String);
42.
-- The predefined operators for this type correspond to those
-- for String
43.
type Duration is delta
implementation-defined range implementation-defined;
44.
-- The predefined operators for the type Duration are the
-- same as for any fixed point type.
45.
-- The predefined exceptions:
46.
Constraint_Error: exception;
Program_Error : exception;
Storage_Error : exception;
Tasking_Error : exception;
47.
end Standard;
48. Standard has no private part.
49. In each of the types Character and Wide_Character, the character literals
for the space character (position 32) and the non-breaking space
character (position 160) correspond to different values. Unless indicated
otherwise, each occurrence of the character literal ' ' in this
International Standard refers to the space character. Similarly, the
character literals for hyphen (position 45) and soft hyphen (position
173) correspond to different values. Unless indicated otherwise, each
occurrence of the character literal '-' in this International Standard
refers to the hyphen character.
Dynamic Semantics
50. Elaboration of the body of Standard has no effect.
Implementation Permissions
51. An implementation may provide additional predefined integer types and
additional predefined floating point types. Not all of these types need
have names.
Implementation Advice
52. If an implementation provides additional named predefined integer types,
then the names should end with ``Integer'' as in ``Long_Integer''. If an
implementation provides additional named predefined floating point types,
then the names should end with ``Float'' as in ``Long_Float''.
NOTES
53. (1) Certain aspects of the predefined entities cannot be completely
described in the language itself. For example, although the enumeration
type Boolean can be written showing the two enumeration literals False
and True, the short-circuit control forms cannot be expressed in the
language.
54. (2) As explained in 8.1: ``Declarative Region'', and 10.1.4: ``The
Compilation Process'', the declarative region of the package Standard
encloses every library unit and consequently the main subprogram; the
declaration of every library unit is assumed to occur within this
declarative region. Library_items are assumed to be ordered in such a way
that there are no forward semantic dependences. However, as explained in
8.3: ``Visibility'', the only library units that are visible within a
given compilation unit are the library units named by all with_clauses
that apply to the given unit, and moreover, within the declarative region
of a given library unit, that library unit itself.
55. (3) If all block_statements of a program are named, then the name of each
program unit can always be written as an expanded name starting with
Standard (unless Standard is itself hidden). The name of a library unit
cannot be a homograph of a name (such as Integer) that is already
declared in Standard.
56. (4) The exception Standard.Numeric_Error is defined in J.6.
ΓòÉΓòÉΓòÉ 17.2. The Package Ada ΓòÉΓòÉΓòÉ
Static Semantics
1. The following language-defined library package exists:
2.
package Ada is
pragma Pure(Ada);
end Ada;
3. Ada serves as the parent of most of the other language-defined library
units; its declaration is empty (except for the pragma Pure).
Legality Rules
4. In the standard mode, it is illegal to compile a child of package Ada.
ΓòÉΓòÉΓòÉ 17.3. Character Handling ΓòÉΓòÉΓòÉ
1. This clause presents the packages related to character processing: an
empty pure package Characters and child packages Characters.Handling and
Characters.Latin_1. The package Characters.Handling provides
classification and conversion functions for Character data, and some
simple functions for dealing with Wide_Character data. The child package
Characters.Latin_1 declares a set of constants initialized to values of
type Character.
A.3.1 The Package Characters
A.3.2 The Package Characters.Handling
A.3.3 The Package Characters.Latin_1
ΓòÉΓòÉΓòÉ 17.3.1. The Package Characters ΓòÉΓòÉΓòÉ
Static Semantics
1. The library package Characters has the following declaration:
2.
package Ada.Characters is
pragma Pure(Characters);
end Ada.Characters;
ΓòÉΓòÉΓòÉ 17.3.2. The Package Characters.Handling ΓòÉΓòÉΓòÉ
Static Semantics
1. The library package Characters.Handling has the following declaration:
2.
package Ada.Characters.Handling is
pragma Preelaborate(Handling);
3.
-- Character classification functions
4.
function Is_Control (Item : in Character) return Boolean;
function Is_Graphic (Item : in Character) return Boolean;
function Is_Letter (Item : in Character) return Boolean;
function Is_Lower (Item : in Character) return Boolean;
function Is_Upper (Item : in Character) return Boolean;
function Is_Basic (Item : in Character) return Boolean;
function Is_Digit (Item : in Character) return Boolean;
function Is_Decimal_Digit (Item : in Character) return Boolean
renames Is_Digit;
function Is_Hexadecimal_Digit (Item : in Character) return Boolean;
function Is_Alphanumeric (Item : in Character) return Boolean;
function Is_Special (Item : in Character) return Boolean;
5.
-- Conversion functions for Character and String
6.
function To_Lower (Item : in Character) return Character;
function To_Upper (Item : in Character) return Character;
function To_Basic (Item : in Character) return Character;
7.
function To_Lower (Item : in String) return String;
function To_Upper (Item : in String) return String;
function To_Basic (Item : in String) return String;
8.
-- Classifications of and conversions
-- between Character and ISO 646
9.
subtype ISO_646 is
Character range Character'Val(0) ┬╖┬╖ Character'Val(127);
10.
function Is_ISO_646 (Item : in Character) return Boolean;
function Is_ISO_646 (Item : in String) return Boolean;
11.
function To_ISO_646 (Item : in Character;
Substitute : in ISO_646 := ' ')
return ISO_646;
12.
function To_ISO_646 (Item : in String;
Substitute : in ISO_646 := ' ')
return String;
13.
-- Classifications of and conversions
-- between Wide_Character and Character.
14.
function Is_Character (Item : in Wide_Character) return Boolean;
function Is_String (Item : in Wide_String) return Boolean;
15.
function To_Character (Item : in Wide_Character;
Substitute : in Character := ' ')
return Character;
16.
function To_String (Item : in Wide_String;
Substitute : in Character := ' ')
return String;
17.
function To_Wide_Character (Item : in Character)
return Wide_Character;
18.
function To_Wide_String (Item : in String) return Wide_String;
19.
end Ada.Characters.Handling;
20. In the description below for each function that returns a Boolean result,
the effect is described in terms of the conditions under which the value
True is returned. If these conditions are not met, then the function
returns False.
21. Each of the following classification functions has a formal Character
parameter, Item, and returns a Boolean result.
22. Is_Control
True if Item is a control character. A control character is
a character whose position is in one of the ranges 0┬╖┬╖31 or
127┬╖┬╖159.
23. Is_Graphic
True if Item is a graphic character. A graphic character is
a character whose position is in one of the ranges 32┬╖┬╖126 or
160┬╖┬╖255.
24. Is_Letter
True if Item is a letter. A letter is a character that is in
one of the ranges 'A'┬╖┬╖'Z' or 'a'┬╖┬╖'z', or whose position is
in one of the ranges 192┬╖┬╖214, 216┬╖┬╖246, or 248┬╖┬╖255.
25. Is_Lower
True if Item is a lower-case letter. A lower-case letter is
a character that is in the range 'a'┬╖┬╖'z', or whose position
is in one of the ranges 223┬╖┬╖246 or 248┬╖┬╖255.
26. Is_Upper
True if Item is an upper-case letter. An upper-case letter
is a character that is in the range 'A'┬╖┬╖'Z' or whose
position is in one of the ranges 192┬╖┬╖214 or 216┬╖┬╖ 222.
27. Is_Basic
True if Item is a basic letter. A basic letter is a
character that is in one of the ranges 'A'┬╖┬╖'Z' and 'a'┬╖┬╖'z',
or that is one of the following: an upper- or lower-case AE
diphthong, an upper- or lower-case Icelandic eth, an upper-
or lower-case Icelandic thorn, or a sharp-s.
28. Is_Digit
True if Item is a decimal digit. A decimal digit is a
character in the range '0'┬╖┬╖'9'.
29. Is_Decimal_Digit
A renaming of Is_Digit.
30. Is_Hexadecimal_Digit
True if Item is a hexadecimal digit. A hexadecimal digit is
a character that is either a decimal digit or that is in one
of the ranges 'A' ┬╖┬╖ 'F' or 'a' ┬╖┬╖ 'f'.
31. Is_Alphanumeric
True if Item is an alphanumeric character. An alphanumeric
character is a character that is either a letter or a decimal
digit.
32. Is_Special
True if Item is a special graphic character. A special
graphic character is a graphic character that is not
alphanumeric.
33. Each of the names To_Lower, To_Upper, and To_Basic refers to two
functions: one that converts from Character to Character, and the other
that converts from String to String. The result of each
Character-to-Character function is described below, in terms of the
conversion applied to Item, its formal Character parameter. The result of
each String-to-String conversion is obtained by applying to each element
of the function's String parameter the corresponding
Character-to-Character conversion; the result is the null String if the
value of the formal parameter is the null String. The lower bound of the
result String is 1.
34. To_Lower
Returns the corresponding lower-case value for Item if
Is_Upper(Item), and returns Item otherwise.
35. To_Upper
Returns the corresponding upper-case value for Item if
Is_Lower(Item) and Item has an upper-case form, and returns Item
otherwise. The lower case letters sharp-s and y-diaeresis do
not have upper case forms.
36. To_Basic
Returns the letter corresponding to Item but with no
diacritical mark, if Item is a letter but not a basic letter;
returns Item otherwise.
37. The following set of functions test for membership in the ISO 646
character range, or convert between ISO 646 and Character.
38. Is_ISO_646
The function whose formal parameter, Item, is of type
Character returns True if Item is in the subtype ISO_646.
39. Is_ISO_646
The function whose formal parameter, Item, is of type String
returns True if Is_ISO_646(Item(I)) is True for each I in
Item'Range.
40. To_ISO_646
The function whose first formal parameter, Item, is of type
Character returns Item if Is_ISO_646(Item), and returns the
Substitute ISO_646 character otherwise.
41. To_ISO_646
The function whose first formal parameter, Item, is of type
String returns the String whose Range is 1┬╖┬╖Item'Length and
each of whose elements is given by To_ISO_646 of the
corresponding element in Item.
42. The following set of functions test Wide_Character values for membership
in Character, or convert between corresponding characters of
Wide_Character and Character.
43. Is_Character
Returns True if Wide_Character'Pos(Item) <=
Character'Pos(Character'Last).
44. Is_String
Returns True if Is_Character(Item(I)) is True for each I in
Item'Range.
45. To_Character
Returns the Character corresponding to Item if
Is_Character(Item), and returns the Substitute Character
otherwise.
46. To_String
Returns the String whose range is 1┬╖┬╖Item'Length and each of
whose elements is given by To_Character of the corresponding
element in Item.
47. To_Wide_Character
Returns the Wide_Character X such that Character'Pos(Item) =
Wide_Character'Pos(X).
48. To_Wide_String
Returns the Wide_String whose range is 1┬╖┬╖Item'Length and
each of whose elements is given by To_Wide_Character of the
corresponding element in Item.
Implementation Advice
49. If an implementation provides a localized definition of Character or
Wide_Character, then the effects of the subprograms in
Characters.Handling should reflect the localizations. See also 3.5.2.
NOTES
50. (5) A basic letter is a letter without a diacritical mark.
51. (6) Except for the hexadecimal digits, basic letters, and ISO_646
characters, the categories identified in the classification functions
form a strict hierarchy:
a. Control characters
b. Graphic characters
1. Alphanumeric characters
a. Letters
1. Upper-case letters
2. Lower-case letters
a. Decimal digits
1. Special graphic characters
ΓòÉΓòÉΓòÉ 17.3.3. The Package Characters.Latin_1 ΓòÉΓòÉΓòÉ
1. The package Characters.Latin_1 declares constants for characters in ISO
8859-1.
Static Semantics
2. The library package Characters.Latin_1 has the following declaration:
3.
package Ada.Characters.Latin_1 is
pragma Pure(Latin_1);
4.
-- Control characters:
5.
NUL : constant Character := Character'Val(0);
SOH : constant Character := Character'Val(1);
STX : constant Character := Character'Val(2);
ETX : constant Character := Character'Val(3);
EOT : constant Character := Character'Val(4);
ENQ : constant Character := Character'Val(5);
ACK : constant Character := Character'Val(6);
BEL : constant Character := Character'Val(7);
BS : constant Character := Character'Val(8);
HT : constant Character := Character'Val(9);
LF : constant Character := Character'Val(10);
VT : constant Character := Character'Val(11);
FF : constant Character := Character'Val(12);
CR : constant Character := Character'Val(13);
SO : constant Character := Character'Val(14);
SI : constant Character := Character'Val(15);
6.
DLE : constant Character := Character'Val(16);
DC1 : constant Character := Character'Val(17);
DC2 : constant Character := Character'Val(18);
DC3 : constant Character := Character'Val(19);
DC4 : constant Character := Character'Val(20);
NAK : constant Character := Character'Val(21);
SYN : constant Character := Character'Val(22);
ETB : constant Character := Character'Val(23);
CAN : constant Character := Character'Val(24);
EM : constant Character := Character'Val(25);
SUB : constant Character := Character'Val(26);
ESC : constant Character := Character'Val(27);
FS : constant Character := Character'Val(28);
GS : constant Character := Character'Val(29);
RS : constant Character := Character'Val(30);
US : constant Character := Character'Val(31);
7.
-- ISO 646 graphic characters:
8.
Space : constant Character := ' ';
-- Character'Val(32)
Exclamation : constant Character := '!';
-- Character'Val(33)
Quotation : constant Character := '"';
-- Character'Val(34)
Number_Sign : constant Character := '#';
-- Character'Val(35)
Dollar_Sign : constant Character := '$';
-- Character'Val(36)
Percent_Sign : constant Character := '%';
-- Character'Val(37)
Ampersand : constant Character := '&';
-- Character'Val(38)
Apostrophe : constant Character := ''';
-- Character'Val(39)
Left_Parenthesis : constant Character := '(';
-- Character'Val(40)
Right_Parenthesis : constant Character := ')';
-- Character'Val(41)
Asterisk : constant Character := '*';
-- Character'Val(42)
Plus_Sign : constant Character := '+';
-- Character'Val(43)
Comma : constant Character := ',';
-- Character'Val(44)
Hyphen : constant Character := '-';
-- Character'Val(45)
Minus_Sign : Character renames Hyphen;
Full_Stop : constant Character := '.';
-- Character'Val(46)
Solidus : constant Character := '/';
-- Character'Val(47)
9.
-- Decimal digits '0' though '9' are at positions 48 through 57
10.
Colon : constant Character := ':';
-- Character'Val(58)
Semicolon : constant Character := ';';
-- Character'Val(59)
Less_Than_Sign : constant Character := '<';
-- Character'Val(60)
Equals_Sign : constant Character := '=';
-- Character'Val(61)
Greater_Than_Sign : constant Character := '>';
-- Character'Val(62)
Question : constant Character := '?';
-- Character'Val(63)
Commercial_At : constant Character := '@';
-- Character'Val(64)
11.
-- Letters 'A' through 'Z' are at positions 65 through 90
12.
Left_Square_Bracket : constant Character := '[';
-- Character'Val(91)
Reverse_Solidus : constant Character := '\';
-- Character'Val(92)
Right_Square_Bracket : constant Character := ']';
-- Character'Val(93)
Circumflex : constant Character := '^';
-- Character'Val(94)
Low_Line : constant Character := '_';
-- Character'Val(95)
13.
Grave : constant Character := '`';
-- Character'Val(96)
LC_A : constant Character := 'a';
-- Character'Val(97)
LC_B : constant Character := 'b';
-- Character'Val(98)
LC_C : constant Character := 'c';
-- Character'Val(99)
LC_D : constant Character := 'd';
-- Character'Val(100)
LC_E : constant Character := 'e';
-- Character'Val(101)
LC_F : constant Character := 'f';
-- Character'Val(102)
LC_G : constant Character := 'g';
-- Character'Val(103)
LC_H : constant Character := 'h';
-- Character'Val(104)
LC_I : constant Character := 'i';
-- Character'Val(105)
LC_J : constant Character := 'j';
-- Character'Val(106)
LC_K : constant Character := 'k';
-- Character'Val(107)
LC_L : constant Character := 'l';
-- Character'Val(108)
LC_M : constant Character := 'm';
-- Character'Val(109)
LC_N : constant Character := 'n';
-- Character'Val(110)
LC_O : constant Character := 'o';
-- Character'Val(111)
14.
LC_P : constant Character := 'p';
-- Character'Val(112)
LC_Q : constant Character := 'q';
-- Character'Val(113)
LC_R : constant Character := 'r';
-- Character'Val(114)
LC_S : constant Character := 's';
-- Character'Val(115)
LC_T : constant Character := 't';
-- Character'Val(116)
LC_U : constant Character := 'u';
-- Character'Val(117)
LC_V : constant Character := 'v';
-- Character'Val(118)
LC_W : constant Character := 'w';
-- Character'Val(119)
LC_X : constant Character := 'x';
-- Character'Val(120)
LC_Y : constant Character := 'y';
-- Character'Val(121)
LC_Z : constant Character := 'z';
-- Character'Val(122)
Left_Curly_Bracket : constant Character := '{';
-- Character'Val(123)
Vertical_Line : constant Character := '|';
-- Character'Val(124)
Right_Curly_Bracket : constant Character := '}';
-- Character'Val(125)
Tilde : constant Character := '~';
-- Character'Val(126)
DEL : constant Character := Character'Val(127);
15.
-- ISO 6429 control characters:
16.
IS4 : Character renames FS;
IS3 : Character renames GS;
IS2 : Character renames RS;
IS1 : Character renames US;
17.
Reserved_128 : constant Character := Character'Val(128);
Reserved_129 : constant Character := Character'Val(129);
BPH : constant Character := Character'Val(130);
NBH : constant Character := Character'Val(131);
Reserved_132 : constant Character := Character'Val(132);
NEL : constant Character := Character'Val(133);
SSA : constant Character := Character'Val(134);
ESA : constant Character := Character'Val(135);
HTS : constant Character := Character'Val(136);
HTJ : constant Character := Character'Val(137);
VTS : constant Character := Character'Val(138);
PLD : constant Character := Character'Val(139);
PLU : constant Character := Character'Val(140);
RI : constant Character := Character'Val(141);
SS2 : constant Character := Character'Val(142);
SS3 : constant Character := Character'Val(143);
18.
DCS : constant Character := Character'Val(144);
PU1 : constant Character := Character'Val(145);
PU2 : constant Character := Character'Val(146);
STS : constant Character := Character'Val(147);
CCH : constant Character := Character'Val(148);
MW : constant Character := Character'Val(149);
SPA : constant Character := Character'Val(150);
EPA : constant Character := Character'Val(151);
19.
SOS : constant Character := Character'Val(152);
Reserved_153 : constant Character := Character'Val(153);
SCI : constant Character := Character'Val(154);
CSI : constant Character := Character'Val(155);
ST : constant Character := Character'Val(156);
OSC : constant Character := Character'Val(157);
PM : constant Character := Character'Val(158);
APC : constant Character := Character'Val(159);
20.
-- Other graphic characters:
21.
-- Character positions 160 (16#A0#) ┬╖┬╖ 175 (16#AF#):
No_Break_Space : constant Character := ' ';
-- Character'Val(160)
NBSP : Character renames No_Break_Space;
Inverted_Exclamation : constant Character :=
Character'Val(161);
Cent_Sign : constant Character :=
Character'Val(162);
Pound_Sign : constant Character :=
Character'Val(163);
Currency_Sign : constant Character :=
Character'Val(164);
Yen_Sign : constant Character :=
Character'Val(165);
Broken_Bar : constant Character :=
Character'Val(166);
Section_Sign : constant Character :=
Character'Val(167);
Diaeresis : constant Character :=
Character'Val(168);
Copyright_Sign : constant Character :=
Character'Val(169);
Feminine_Ordinal_Indicator : constant Character :=
Character'Val(170);
Left_Angle_Quotation : constant Character :=
Character'Val(171);
Not_Sign : constant Character :=
Character'Val(172);
Soft_Hyphen : constant Character :=
Character'Val(173);
Registered_Trade_Mark_Sign : constant Character :=
Character'Val(174);
Macron : constant Character :=
Character'Val(175);
22.
-- Character positions 176 (16#B0#) ┬╖┬╖ 191 (16#BF#):
Degree_Sign : constant Character :=
Character'Val(176);
Ring_Above : Character renames Degree_Sign;
Plus_Minus_Sign : constant Character :=
Character'Val(177);
Superscript_Two : constant Character :=
Character'Val(178);
Superscript_Three : constant Character :=
Character'Val(179);
Acute : constant Character :=
Character'Val(180);
Micro_Sign : constant Character :=
Character'Val(181);
Pilcrow_Sign : constant Character :=
Character'Val(182);
Paragraph_Sign : Character renames Pilcrow_Sign;
Middle_Dot : constant Character :=
Character'Val(183);
Cedilla : constant Character :=
Character'Val(184);
Superscript_One : constant Character :=
Character'Val(185);
Masculine_Ordinal_Indicator : constant Character :=
Character'Val(186);
Right_Angle_Quotation : constant Character :=
Character'Val(187);
Fraction_One_Quarter : constant Character :=
Character'Val(188);
Fraction_One_Half : constant Character :=
Character'Val(189);
Fraction_Three_Quarters : constant Character :=
Character'Val(190);
Inverted_Question : constant Character :=
Character'Val(191);
23.
-- Character positions 192 (16#C0#) ┬╖┬╖ 207 (16#CF#):
UC_A_Grave : constant Character :=
Character'Val(192);
UC_A_Acute : constant Character :=
Character'Val(193);
UC_A_Circumflex : constant Character :=
Character'Val(194);
UC_A_Tilde : constant Character :=
Character'Val(195);
UC_A_Diaeresis : constant Character :=
Character'Val(196);
UC_A_Ring : constant Character :=
Character'Val(197);
UC_AE_Diphthong : constant Character :=
Character'Val(198);
UC_C_Cedilla : constant Character :=
Character'Val(199);
UC_E_Grave : constant Character :=
Character'Val(200);
UC_E_Acute : constant Character :=
Character'Val(201);
UC_E_Circumflex : constant Character :=
Character'Val(202);
UC_E_Diaeresis : constant Character :=
Character'Val(203);
UC_I_Grave : constant Character :=
Character'Val(204);
UC_I_Acute : constant Character :=
Character'Val(205);
UC_I_Circumflex : constant Character :=
Character'Val(206);
UC_I_Diaeresis : constant Character :=
Character'Val(207);
24.
-- Character positions 208 (16#D0#) ┬╖┬╖ 223 (16#DF#):
UC_Icelandic_Eth : constant Character :=
Character'Val(208);
UC_N_Tilde : constant Character :=
Character'Val(209);
UC_O_Grave : constant Character :=
Character'Val(210);
UC_O_Acute : constant Character :=
Character'Val(211);
UC_O_Circumflex : constant Character :=
Character'Val(212);
UC_O_Tilde : constant Character :=
Character'Val(213);
UC_O_Diaeresis : constant Character :=
Character'Val(214);
Multiplication_Sign : constant Character :=
Character'Val(215);
UC_O_Oblique_Stroke : constant Character :=
Character'Val(216);
UC_U_Grave : constant Character :=
Character'Val(217);
UC_U_Acute : constant Character :=
Character'Val(218);
UC_U_Circumflex : constant Character :=
Character'Val(219);
UC_U_Diaeresis : constant Character :=
Character'Val(220);
UC_Y_Acute : constant Character :=
Character'Val(221);
UC_Icelandic_Thorn : constant Character :=
Character'Val(222);
LC_German_Sharp_S : constant Character :=
Character'Val(223);
25.
-- Character positions 224 (16#E0#) ┬╖┬╖ 239 (16#EF#):
LC_A_Grave : constant Character :=
Character'Val(224);
LC_A_Acute : constant Character :=
Character'Val(225);
LC_A_Circumflex : constant Character :=
Character'Val(226);
LC_A_Tilde : constant Character :=
Character'Val(227);
LC_A_Diaeresis : constant Character :=
Character'Val(228);
LC_A_Ring : constant Character :=
Character'Val(229);
LC_AE_Diphthong : constant Character :=
Character'Val(230);
LC_C_Cedilla : constant Character :=
Character'Val(231);
LC_E_Grave : constant Character :=
Character'Val(232);
LC_E_Acute : constant Character :=
Character'Val(233);
LC_E_Circumflex : constant Character :=
Character'Val(234);
LC_E_Diaeresis : constant Character :=
Character'Val(235);
LC_I_Grave : constant Character :=
Character'Val(236);
LC_I_Acute : constant Character :=
Character'Val(237);
LC_I_Circumflex : constant Character :=
Character'Val(238);
LC_I_Diaeresis : constant Character :=
Character'Val(239);
26.
-- Character positions 240 (16#F0#) ┬╖┬╖ 255 (16#FF#):
LC_Icelandic_Eth : constant Character :=
Character'Val(240);
LC_N_Tilde : constant Character :=
Character'Val(241);
LC_O_Grave : constant Character :=
Character'Val(242);
LC_O_Acute : constant Character :=
Character'Val(243);
LC_O_Circumflex : constant Character :=
Character'Val(244);
LC_O_Tilde : constant Character :=
Character'Val(245);
LC_O_Diaeresis : constant Character :=
Character'Val(246);
Division_Sign : constant Character :=
Character'Val(247);
LC_O_Oblique_Stroke : constant Character :=
Character'Val(248);
LC_U_Grave : constant Character :=
Character'Val(249);
LC_U_Acute : constant Character :=
Character'Val(250);
LC_U_Circumflex : constant Character :=
Character'Val(251);
LC_U_Diaeresis : constant Character :=
Character'Val(252);
LC_Y_Acute : constant Character :=
Character'Val(253);
LC_Icelandic_Thorn : constant Character :=
Character'Val(254);
LC_Y_Diaeresis : constant Character :=
Character'Val(255);
end Ada.Characters.Latin_1;
Implementation Permissions
27. An implementation may provide additional packages as children of
Ada.Characters, to declare names for the symbols of the local character
set or other character sets.
ΓòÉΓòÉΓòÉ 17.4. String Handling ΓòÉΓòÉΓòÉ
1. This clause presents the specifications of the package Strings and
several child packages, which provide facilities for dealing with string
data. Fixed-length, bounded-length, and unbounded-length strings are
supported, for both String and Wide_String. The string-handling
subprograms include searches for pattern strings and for characters in
program-specified sets, translation (via a character-to-character
mapping), and transformation (replacing, inserting, overwriting, and
deleting of substrings).
A.4.1 The Package Strings
A.4.2 The Package Strings.Maps
A.4.3 Fixed-Length String Handling
A.4.4 Bounded-Length String Handling
A.4.5 Unbounded-Length String Handling
A.4.6 String-Handling Sets and Mappings
A.4.7 Wide_String Handling
ΓòÉΓòÉΓòÉ 17.4.1. The Package Strings ΓòÉΓòÉΓòÉ
1. The package Strings provides declarations common to the string handling
packages.
Static Semantics
2. The library package Strings has the following declaration:
3.
package Ada.Strings is
pragma Pure(Strings);
4.
Space : constant Character := ' ';
Wide_Space : constant Wide_Character := ' ';
5.
Length_Error, Pattern_Error, Index_Error, Translation_Error
: exception;
6.
type Alignment is (Left, Right, Center);
type Truncation is (Left, Right, Error);
type Membership is (Inside, Outside);
type Direction is (Forward, Backward);
type Trim_End is (Left, Right, Both);
end Ada.Strings;
ΓòÉΓòÉΓòÉ 17.4.2. The Package Strings.Maps ΓòÉΓòÉΓòÉ
1. The package Strings.Maps defines the types, operations, and other
entities needed for character sets and character-to-character mappings.
Static Semantics
2. The library package Strings.Maps has the following declaration:
3.
package Ada.Strings.Maps is
pragma Preelaborate(Maps);
4.
-- Representation for a set of character values:
type Character_Set is private;
5.
Null_Set : constant Character_Set;
6.
type Character_Range is
record
Low : Character;
High : Character;
end record;
-- Represents Character range Low┬╖┬╖High
7.
type Character_Ranges is
array (Positive range <>) of Character_Range;
8.
function To_Set (Ranges : in Character_Ranges)
return Character_Set;
9.
function To_Set (Span : in Character_Range)
return Character_Set;
10.
function To_Ranges (Set : in Character_Set)
return Character_Ranges;
11.
function "=" (Left, Right : in Character_Set) return Boolean;
12.
function "not" (Right : in Character_Set)
return Character_Set;
function "and" (Left, Right : in Character_Set)
return Character_Set;
function "or" (Left, Right : in Character_Set)
return Character_Set;
function "xor" (Left, Right : in Character_Set)
return Character_Set;
function "-" (Left, Right : in Character_Set)
return Character_Set;
13.
function Is_In (Element : in Character;
Set : in Character_Set)
return Boolean;
14.
function Is_Subset (Elements : in Character_Set;
Set : in Character_Set)
return Boolean;
15.
function "<=" (Left : in Character_Set;
Right : in Character_Set)
return Boolean renames Is_Subset;
16.
-- Alternative representation for a set of character values:
subtype Character_Sequence is String;
17.
function To_Set (Sequence : in Character_Sequence)
return Character_Set;
18.
function To_Set (Singleton : in Character) return Character_Set;
19.
function To_Sequence (Set : in Character_Set)
return Character_Sequence;
20.
-- Representation for a character to character mapping:
type Character_Mapping is private;
21.
function Value (Map : in Character_Mapping;
Element : in Character)
return Character;
22.
Identity : constant Character_Mapping;
23.
function To_Mapping (From, To : in Character_Sequence)
return Character_Mapping;
24.
function To_Domain (Map : in Character_Mapping)
return Character_Sequence;
function To_Range (Map : in Character_Mapping)
return Character_Sequence;
25.
type Character_Mapping_Function is
access function (From : in Character) return Character;
26.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Strings.Maps;
27. An object of type Character_Set represents a set of characters.
28. Null_Set represents the set containing no characters.
29. An object Obj of type Character_Range represents the set of characters in
the range Obj.Low ┬╖┬╖ Obj.High.
30. An object Obj of type Character_Ranges represents the union of the sets
corresponding to Obj(I) for I in Obj'Range.
31.
function To_Set (Ranges : in Character_Ranges) return Character_Set;
a. If Ranges'Length=0 then Null_Set is returned; otherwise the returned
value represents the set corresponding to Ranges.
1.
function To_Set (Span : in Character_Range) return Character_Set;
a. The returned value represents the set containing each character in
Span.
1.
function To_Ranges (Set : in Character_Set) return Character_Ranges;
a. If Set = Null_Set then an empty Character_Ranges array is returned;
otherwise the shortest array of contiguous ranges of Character
values in Set, in increasing order of Low, is returned.
1.
function "=" (Left, Right : in Character_Set) return Boolean;
a. The function "=" returns True if Left and Right represent identical
sets, and False otherwise.
1. Each of the logical operators "not", "and", "or", and "xor" returns a
Character_Set value that represents the set obtained by applying the
corresponding operation to the set(s) represented by the parameter(s) of
the operator. "-"(Left, Right) is equivalent to "and"(Left,
"not"(Right)).
2.
function Is_In (Element : in Character;
Set : in Character_Set);
return Boolean;
a. Is_In returns True if Element is in Set, and False otherwise.
1.
function Is_Subset (Elements : in Character_Set;
Set : in Character_Set)
return Boolean;
a. Is_Subset returns True if Elements is a subset of Set, and False
otherwise.
1.
subtype Character_Sequence is String;
a. The Character_Sequence subtype is used to portray a set of character
values and also to identify the domain and range of a character
mapping.
1.
function To_Set (Sequence : in Character_Sequence)
return Character_Set;
function To_Set (Singleton : in Character)
return Character_Set;
a. Sequence portrays the set of character values that it explicitly
contains (ignoring duplicates). Singleton portrays the set
comprising a single Character. Each of the To_Set functions returns
a Character_Set value that represents the set portrayed by Sequence
or Singleton.
1.
function To_Sequence (Set : in Character_Set)
return Character_Sequence;
a. The function To_Sequence returns a Character_Sequence value
containing each of the characters in the set represented by Set, in
ascending order with no duplicates.
1.
type Character_Mapping is private;
a. An object of type Character_Mapping represents a
Character-to-Character mapping.
1.
function Value (Map : in Character_Mapping;
Element : in Character)
return Character;
a. The function Value returns the Character value to which Element maps
with respect to the mapping represented by Map.
1. A character C matches a pattern character P with respect to a given
Character_Mapping value Map if Value(Map, C) = P. A string S matches a
pattern string P with respect to a given Character_Mapping if their
lengths are the same and if each character in S matches its corresponding
character in the pattern string P.
2. String handling subprograms that deal with character mappings have
parameters whose type is Character_Mapping.
3.
Identity : constant Character_Mapping;
a. Identity maps each Character to itself.
1.
function To_Mapping (From, To : in Character_Sequence)
return Character_Mapping;
a. To_Mapping produces a Character_Mapping such that each element of
From maps to the corresponding element of To, and each other
character maps to itself. If From'Length /= To'Length, or if some
character is repeated in From, then Translation_Error is propagated.
1.
function To_Domain (Map : in Character_Mapping)
return Character_Sequence;
a. To_Domain returns the shortest Character_Sequence value D such that
each character not in D maps to itself, and such that the characters
in D are in ascending order. The lower bound of D is 1.
1.
function To_Range (Map : in Character_Mapping)
return Character_Sequence;
a. To_Range returns the Character_Sequence value R, with lower bound 1
and upper bound Map'Length, such that if D = To_Domain(Map) then
D(I) maps to R(I) for each I in D'Range.
1. An object F of type Character_Mapping_Function maps a Character value C
to the Character value F.all(C), which is said to match C with respect to
mapping function F.
NOTES
2. (7) Character_Mapping and Character_Mapping_Function are used both for
character equivalence mappings in the search subprograms (such as for
case insensitivity) and as transformational mappings in the Translate
subprograms.
3. (8) To_Domain(Identity) and To_Range(Identity) each returns the null
string.
Examples
4. To_Mapping("ABCD", "ZZAB") returns a Character_Mapping that maps 'A' and
'B' to 'Z', 'C' to 'A', 'D' to 'B', and each other Character to itself.
ΓòÉΓòÉΓòÉ 17.4.3. Fixed-Length String Handling ΓòÉΓòÉΓòÉ
1. The language-defined package Strings.Fixed provides string-handling
subprograms for fixed-length strings; that is, for values of type
Standard.String. Several of these subprograms are procedures that modify
the contents of a String that is passed as an out or an in out parameter;
each has additional parameters to control the effect when the logical
length of the result differs from the parameter's length.
2. For each function that returns a String, the lower bound of the returned
value is 1.
3. The basic model embodied in the package is that a fixed-length string
comprises significant characters and possibly padding (with space
characters) on either or both ends. When a shorter string is copied to a
longer string, padding is inserted, and when a longer string is copied to
a shorter one, padding is stripped. The Move procedure in Strings.Fixed,
which takes a String as an out parameter, allows the programmer to
control these effects. Similar control is provided by the string
transformation procedures.
Static Semantics
4. The library package Strings.Fixed has the following declaration:
5.
with Ada.Strings.Maps;
package Ada.Strings.Fixed is
pragma Preelaborate(Fixed);
6.
-- "Copy" procedure for strings of possibly different lengths
7.
procedure Move (Source : in String;
Target : out String;
Drop : in Truncation := Error;
Justify : in Alignment := Left;
Pad : in Character := Space);
8.
-- Search subprograms
9.
function Index (Source : in String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
10.
function Index (Source : in String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
11.
function Index (Source : in String;
Set : in Maps.Character_Set;
Test : in Membership := Inside;
Going : in Direction := Forward)
return Natural;
12.
function Index_Non_Blank (Source : in String;
Going : in Direction := Forward)
return Natural;
13.
function Count (Source : in String;
Pattern : in String;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
14.
function Count (Source : in String;
Pattern : in String;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
15.
function Count (Source : in String;
Set : in Maps.Character_Set)
return Natural;
16.
procedure Find_Token (Source : in String;
Set : in Maps.Character_Set;
Test : in Membership;
First : out Positive;
Last : out Natural);
17.
-- String translation subprograms
18.
function Translate (Source : in String;
Mapping : in Maps.Character_Mapping)
return String;
19.
procedure Translate (Source : in out String;
Mapping : in Maps.Character_Mapping);
20.
function Translate (Source : in String;
Mapping : in Maps.Character_Mapping_Function)
return String;
21.
procedure Translate
(Source : in out String;
Mapping : in Maps.Character_Mapping_Function);
22.
-- String transformation subprograms
23.
function Replace_Slice (Source : in String;
Low : in Positive;
High : in Natural;
By : in String)
return String;
24.
procedure Replace_Slice (Source : in out String;
Low : in Positive;
High : in Natural;
By : in String;
Drop : in Truncation := Error;
Justify : in Alignment := Left;
Pad : in Character := Space);
25.
function Insert (Source : in String;
Before : in Positive;
New_Item : in String)
return String;
26.
procedure Insert (Source : in out String;
Before : in Positive;
New_Item : in String;
Drop : in Truncation := Error);
27.
function Overwrite (Source : in String;
Position : in Positive;
New_Item : in String)
return String;
28.
procedure Overwrite (Source : in out String;
Position : in Positive;
New_Item : in String;
Drop : in Truncation := Right);
29.
function Delete (Source : in String;
From : in Positive;
Through : in Natural)
return String;
30.
procedure Delete (Source : in out String;
From : in Positive;
Through : in Natural;
Justify : in Alignment := Left;
Pad : in Character := Space);
31.
-- String selector subprograms
function Trim (Source : in String;
Side : in Trim_End)
return String;
32.
procedure Trim (Source : in out String;
Side : in Trim_End;
Justify : in Alignment := Left;
Pad : in Character := Space);
33.
function Trim (Source : in String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set)
return String;
34.
procedure Trim (Source : in out String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set;
Justify : in Alignment := Strings.Left;
Pad : in Character := Space);
35.
function Head (Source : in String;
Count : in Natural;
Pad : in Character := Space)
return String;
36.
procedure Head (Source : in out String;
Count : in Natural;
Justify : in Alignment := Left;
Pad : in Character := Space);
37.
function Tail (Source : in String;
Count : in Natural;
Pad : in Character := Space)
return String;
38.
procedure Tail (Source : in out String;
Count : in Natural;
Justify : in Alignment := Left;
Pad : in Character := Space);
39.
--String constructor functions
40.
function "*" (Left : in Natural;
Right : in Character) return String;
41.
function "*" (Left : in Natural;
Right : in String) return String;
42.
end Ada.Strings.Fixed;
43. The effects of the above subprograms are as follows.
44.
procedure Move (Source : in String;
Target : out String;
Drop : in Truncation := Error;
Justify : in Alignment := Left;
Pad : in Character := Space);
a. The Move procedure copies characters from Source to Target. If
Source has the same length as Target, then the effect is to assign
Source to Target. If Source is shorter than Target then:
1. If Justify=Left, then Source is copied into the first
Source'Length characters of Target.
2. If Justify=Right, then Source is copied into the last
Source'Length characters of Target.
3. If Justify=Center, then Source is copied into the middle
Source'Length characters of Target. In this case, if the
difference in length between Target and Source is odd, then the
extra Pad character is on the right.
4. Pad is copied to each Target character not otherwise assigned.
a. If Source is longer than Target, then the effect is based on Drop.
1. If Drop=Left, then the rightmost Target'Length characters of
Source are copied into Target.
2. If Drop=Right, then the leftmost Target'Length characters of
Source are copied into Target.
3. If Drop=Error, then the effect depends on the value of the
Justify parameter and also on whether any characters in Source
other than Pad would fail to be copied:
a. If Justify=Left, and if each of the rightmost
Source'Length-Target'Length characters in Source is Pad,
then the leftmost Target'Length characters of Source are
copied to Target.
b. If Justify=Right, and if each of the leftmost
Source'Length-Target'Length characters in Source is Pad,
then the rightmost Target'Length characters of Source are
copied to Target.
c. Otherwise, Length_Error is propagated.
1.
function Index (Source : in String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
function Index (Source : in String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
a. Each Index function searches for a slice of Source, with length
Pattern'Length, that matches Pattern with respect to Mapping; the
parameter Going indicates the direction of the lookup. If Going =
Forward, then Index returns the smallest index I such that the slice
of Source starting at I matches Pattern. If Going = Backward, then
Index returns the largest index I such that the slice of Source
starting at I matches Pattern. If there is no such slice, then 0 is
returned. If Pattern is the null string then Pattern_Error is
1.
function Index (Source : in String;
Set : in Maps.Character_Set;
Test : in Membership := Inside;
Going : in Direction := Forward)
return Natural;
a. Index searches for the first or last occurrence of any of a set of
characters (when Test=Inside), or any of the complement of a set of
characters (when Test=Outside). It returns the smallest index I (if
Going=Forward) or the largest index I (if Going=Backward) such that
Source(I) satisfies the Test condition with respect to Set; it
returns 0 if there is no such Character in Source.
1.
function Index_Non_Blank (Source : in String;
Going : in Direction := Forward)
return Natural;
a. Returns Index(Source, Maps.To_Set(Space), Outside, Going)
1.
function Count (Source : in String;
Pattern : in String;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
function Count (Source : in String;
Pattern : in String;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
a. Returns the maximum number of nonoverlapping slices of Source that
match Pattern with respect to Mapping. If Pattern is the null string
then Pattern_Error is propagated.
1.
function Count (Source : in String;
Set : in Maps.Character_Set)
return Natural;
a. Returns the number of occurrences in Source of characters that are
in Set.
1.
procedure Find_Token (Source : in String;
Set : in Maps.Character_Set;
Test : in Membership;
First : out Positive;
Last : out Natural);
a. Find_Token returns in First and Last the indices of the beginning
and end of the first slice of Source all of whose elements satisfy
the Test condition, and such that the elements (if any) immediately
before and after the slice do not satisfy the Test condition. If no
such slice exists, then the value returned for Last is zero, and the
value returned for First is Source'First.
1.
function Translate (Source : in String;
Mapping : in Maps.Character_Mapping)
return String;
function Translate (Source : in String;
Mapping : in Maps.Character_Mapping_Function)
return String;
a. Returns the string S whose length is Source'Length and such that
S(I) is the character to which Mapping maps the corresponding
element of Source, for I in 1┬╖┬╖Source'Length.
1.
procedure Translate (Source : in out String;
Mapping : in Maps.Character_Mapping);
procedure Translate (Source : in out String;
Mapping : in Maps.Character_Mapping_Function);
a. Equivalent to Source := Translate(Source, Mapping).
1.
function Replace_Slice (Source : in String;
Low : in Positive;
High : in Natural;
By : in String)
return String;
a. If Low > Source'Last+1, or High < Source'First-1, then Index_Error
is propagated. Otherwise, if High >= Low then the returned string
comprises Source(Source'First┬╖┬╖Low-1) & By &
Source(High+1┬╖┬╖Source'Last), and if High < Low then the returned
string is Insert(Source, Before=>Low, New_Item=>By).
1.
procedure Replace_Slice (Source : in out String;
Low : in Positive;
High : in Natural;
By : in String;
Drop : in Truncation := Error;
Justify : in Alignment := Left;
Pad : in Character := Space);
a. Equivalent to Move(Replace_Slice(Source, Low, High, By), Source,
Drop, Justify, Pad).
1.
function Insert (Source : in String;
Before : in Positive;
New_Item : in String)
return String;
Propagates Index_Error if Before is not in Source'First ┬╖┬╖
Source'Last+1; otherwise returns Source(Source'First┬╖┬╖Before-1) &
New_Item & Source(Before┬╖┬╖Source'Last), but with lower bound 1.
1.
procedure Insert (Source : in out String;
Before : in Positive;
New_Item : in String;
Drop : in Truncation := Error);
a. Equivalent to Move(Insert(Source, Before, New_Item), Source, Drop).
1.
function Overwrite (Source : in String;
Position : in Positive;
New_Item : in String)
return String;
a. Propagates Index_Error if Position is not in Source'First ┬╖┬╖
Source'Last+1; otherwise returns the string obtained from Source by
consecutively replacing characters starting at Position with
corresponding characters from New_Item. If the end of Source is
reached before the characters in New_Item are exhausted, the
remaining characters from New_Item are appended to the string.
1.
procedure Overwrite (Source : in out String;
Position : in Positive;
New_Item : in String;
Drop : in Truncation := Right);
a. Equivalent to Move(Overwrite(Source, Position, New_Item), Source,
Drop).
1.
function Delete (Source : in String;
From : in Positive;
Through : in Natural)
return String;
a. If From <= Through, the returned string is Replace_Slice(Source,
From, Through, ""), otherwise it is Source.
1.
procedure Delete (Source : in out String;
From : in Positive;
Through : in Natural;
Justify : in Alignment := Left;
Pad : in Character := Space);
a. Equivalent to Move(Delete(Source, From, Through), Source, Justify =>
Justify, Pad => Pad).
1.
function Trim (Source : in String;
Side : in Trim_End)
return String;
a. Returns the string obtained by removing from Source all leading
Space characters (if Side = Left), all trailing Space characters (if
Side = Right), or all leading and trailing Space characters (if Side
= Both).
1.
procedure Trim (Source : in out String;
Side : in Trim_End;
Justify : in Alignment := Left;
Pad : in Character := Space);
a. Equivalent to Move(Trim(Source, Side), Source, Justify=>Justify,
Pad=>Pad).
1.
function Trim (Source : in String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set)
return String;
a. Returns the string obtained by removing from Source all leading
characters in Left and all trailing characters in Right.
1.
procedure Trim (Source : in out String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set;
Justify : in Alignment := Strings.Left;
Pad : in Character := Space);
a. Equivalent to Move(Trim(Source, Left, Right), Source, Justify =>
Justify, Pad=>Pad).
1.
function Head (Source : in String;
Count : in Natural;
Pad : in Character := Space)
return String;
a. Returns a string of length Count. If Count <= Source'Length, the
string comprises the first Count characters of Source. Otherwise its
contents are Source concatenated with Count-Source'Length Pad
characters.
1.
procedure Head (Source : in out String;
Count : in Natural;
Justify : in Alignment := Left;
Pad : in Character := Space);
a. Equivalent to Move(Head(Source, Count, Pad), Source, Drop=>Error,
Justify=>Justify, Pad=>Pad).
1.
function Tail (Source : in String;
Count : in Natural;
Pad : in Character := Space)
return String;
a. Returns a string of length Count. If Count <= Source'Length, the
string comprises the last Count characters of Source. Otherwise its
contents are Count-Source'Length Pad characters concatenated with
Source.
1.
procedure Tail (Source : in out String;
Count : in Natural;
Justify : in Alignment := Left;
Pad : in Character := Space);
a. Equivalent to Move(Tail(Source, Count, Pad), Source, Drop=>Error,
Justify=>Justify, Pad=>Pad).
1.
function "*" (Left : in Natural;
Right : in Character) return String;
function "*" (Left : in Natural;
Right : in String) return String;
a. These functions replicate a character or string a specified number
of times. The first function returns a string whose length is Left
and each of whose elements is Right. The second function returns a
string whose length is Left*Right'Length and whose value is the null
string if Left = 0 and is (Left-1)*Right & Right otherwise.
NOTES
1. (9) In the Index and Count functions taking Pattern and Mapping
parameters, the actual String parameter passed to Pattern should comprise
characters occurring as target characters of the mapping. Otherwise the
pattern will not match.
2. (10) In the Insert subprograms, inserting at the end of a string is
obtained by passing Source'Last+1 as the Before parameter.
3. (11) If a null Character_Mapping_Function is passed to any of the string
handling subprograms, Constraint_Error is propagated.
ΓòÉΓòÉΓòÉ 17.4.4. Bounded-Length String Handling ΓòÉΓòÉΓòÉ
1. The language-defined package Strings.Bounded provides a generic package
each of whose instances yields a private type Bounded_String and a set of
operations. An object of a particular Bounded_String type represents a
String whose low bound is 1 and whose length can vary conceptually
between 0 and a maximum size established at the generic instantiation.
The subprograms for fixed-length string handling are either overloaded
directly for Bounded_String, or are modified as needed to reflect the
variability in length. Additionally, since the Bounded_String type is
private, appropriate constructor and selector operations are provided.
Static Semantics
2. The library package Strings.Bounded has the following declaration:
3.
with Ada.Strings.Maps;
package Ada.Strings.Bounded is
pragma Preelaborate(Bounded);
4.
generic
Max : Positive; -- Maximum length of a Bounded_String
package Generic_Bounded_Length is
5.
Max_Length : constant Positive := Max;
6.
type Bounded_String is private;
7.
Null_Bounded_String : constant Bounded_String;
8.
subtype Length_Range is Natural range 0 ┬╖┬╖ Max_Length;
9.
function Length (Source : in Bounded_String)
return Length_Range;
10.
-- Conversion, Concatenation, and Selection functions
11.
function To_Bounded_String (Source : in String;
Drop : in Truncation := Error)
return Bounded_String;
12.
function To_String (Source : in Bounded_String) return String;
13.
function Append (Left, Right : in Bounded_String;
Drop : in Truncation := Error)
return Bounded_String;
14.
function Append (Left : in Bounded_String;
Right : in String;
Drop : in Truncation := Error)
return Bounded_String;
15.
function Append (Left : in String;
Right : in Bounded_String;
Drop : in Truncation := Error)
return Bounded_String;
16.
function Append (Left : in Bounded_String;
Right : in Character;
Drop : in Truncation := Error)
return Bounded_String;
17.
function Append (Left : in Character;
Right : in Bounded_String;
Drop : in Truncation := Error)
return Bounded_String;
18.
procedure Append (Source : in out Bounded_String;
New_Item : in Bounded_String;
Drop : in Truncation := Error);
19.
procedure Append (Source : in out Bounded_String;
New_Item : in String;
Drop : in Truncation := Error);
20.
procedure Append (Source : in out Bounded_String;
New_Item : in Character;
Drop : in Truncation := Error);
21.
function "&" (Left, Right : in Bounded_String)
return Bounded_String;
22.
function "&" (Left : in Bounded_String; Right : in String)
return Bounded_String;
23.
function "&" (Left : in String; Right : in Bounded_String)
return Bounded_String;
24.
function "&" (Left : in Bounded_String; Right : in Character)
return Bounded_String;
25.
function "&" (Left : in Character; Right : in Bounded_String)
return Bounded_String;
26.
function Element (Source : in Bounded_String;
Index : in Positive)
return Character;
27.
procedure Replace_Element (Source : in out Bounded_String;
Index : in Positive;
By : in Character);
28.
function Slice (Source : in Bounded_String;
Low : in Positive;
High : in Natural)
return String;
29.
function "=" (Left, Right : in Bounded_String) return Boolean;
function "=" (Left : in Bounded_String; Right : in String)
return Boolean;
30.
function "=" (Left : in String; Right : in Bounded_String)
return Boolean;
31.
function "<" (Left, Right : in Bounded_String) return Boolean;
32.
function "<" (Left : in Bounded_String; Right : in String)
return Boolean;
33.
function "<" (Left : in String; Right : in Bounded_String)
return Boolean;
34.
function "<=" (Left, Right : in Bounded_String) return Boolean;
35.
function "<=" (Left : in Bounded_String; Right : in String)
return Boolean;
36.
function "<=" (Left : in String; Right : in Bounded_String)
return Boolean;
37.
function ">" (Left, Right : in Bounded_String) return Boolean;
38.
function ">" (Left : in Bounded_String; Right : in String)
return Boolean;
39.
function ">" (Left : in String; Right : in Bounded_String)
return Boolean;
40.
function ">=" (Left, Right : in Bounded_String) return Boolean;
41.
function ">=" (Left : in Bounded_String; Right : in String)
return Boolean;
42.
function ">=" (Left : in String; Right : in Bounded_String)
return Boolean;
43.
-- Search functions
44.
function Index (Source : in Bounded_String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
45.
function Index (Source : in Bounded_String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
46.
function Index (Source : in Bounded_String;
Set : in Maps.Character_Set;
Test : in Membership := Inside;
Going : in Direction := Forward)
return Natural;
47.
function Index_Non_Blank (Source : in Bounded_String;
Going : in Direction := Forward)
return Natural;
48.
function Count (Source : in Bounded_String;
Pattern : in String;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
49.
function Count (Source : in Bounded_String;
Pattern : in String;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
50.
function Count (Source : in Bounded_String;
Set : in Maps.Character_Set)
return Natural;
51.
procedure Find_Token (Source : in Bounded_String;
Set : in Maps.Character_Set;
Test : in Membership;
First : out Positive;
Last : out Natural);
52.
-- String translation subprograms
53.
function Translate (Source : in Bounded_String;
Mapping : in Maps.Character_Mapping)
return Bounded_String;
54.
procedure Translate (Source : in out Bounded_String;
Mapping : in Maps.Character_Mapping);
55.
function Translate
(Source : in Bounded_String;
Mapping : in Maps.Character_Mapping_Function)
return Bounded_String;
56.
procedure Translate
(Source : in out Bounded_String;
Mapping : in Maps.Character_Mapping_Function);
57.
-- String transformation subprograms
58.
function Replace_Slice (Source : in Bounded_String;
Low : in Positive;
High : in Natural;
By : in String;
Drop : in Truncation := Error)
return Bounded_String;
59.
procedure Replace_Slice (Source : in out Bounded_String;
Low : in Positive;
High : in Natural;
By : in String;
Drop : in Truncation := Error);
60.
function Insert (Source : in Bounded_String;
Before : in Positive;
New_Item : in String;
Drop : in Truncation := Error)
return Bounded_String;
61.
procedure Insert (Source : in out Bounded_String;
Before : in Positive;
New_Item : in String;
Drop : in Truncation := Error);
62.
function Overwrite (Source : in Bounded_String;
Position : in Positive;
New_Item : in String;
Drop : in Truncation := Error)
return Bounded_String;
63.
procedure Overwrite (Source : in out Bounded_String;
Position : in Positive;
New_Item : in String;
Drop : in Truncation := Error);
64.
function Delete (Source : in Bounded_String;
From : in Positive;
Through : in Natural)
return Bounded_String;
65.
procedure Delete (Source : in out Bounded_String;
From : in Positive;
Through : in Natural);
66.
-- String selector subprograms
67.
function Trim (Source : in Bounded_String;
Side : in Trim_End)
return Bounded_String;
procedure Trim (Source : in out Bounded_String;
Side : in Trim_End);
68.
function Trim (Source : in Bounded_String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set)
return Bounded_String;
69.
procedure Trim (Source : in out Bounded_String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set);
70.
function Head (Source : in Bounded_String;
Count : in Natural;
Pad : in Character := Space;
Drop : in Truncation := Error)
return Bounded_String;
71.
procedure Head (Source : in out Bounded_String;
Count : in Natural;
Pad : in Character := Space;
Drop : in Truncation := Error);
72.
function Tail (Source : in Bounded_String;
Count : in Natural;
Pad : in Character := Space;
Drop : in Truncation := Error)
return Bounded_String;
73.
procedure Tail (Source : in out Bounded_String;
Count : in Natural;
Pad : in Character := Space;
Drop : in Truncation := Error);
74.
-- String constructor subprograms
75.
function "*" (Left : in Natural;
Right : in Character)
return Bounded_String;
76.
function "*" (Left : in Natural;
Right : in String)
return Bounded_String;
77.
function "*" (Left : in Natural;
Right : in Bounded_String)
return Bounded_String;
78.
function Replicate (Count : in Natural;
Item : in Character;
Drop : in Truncation := Error)
return Bounded_String;
79.
function Replicate (Count : in Natural;
Item : in String;
Drop : in Truncation := Error)
return Bounded_String;
80.
function Replicate (Count : in Natural;
Item : in Bounded_String;
Drop : in Truncation := Error)
return Bounded_String;
81.
private
┬╖┬╖┬╖ -- not specified by the language
end Generic_Bounded_Length;
82.
end Ada.Strings.Bounded;
83. Null_Bounded_String represents the null string. If an object of type
Bounded_String is not otherwise initialized, it will be initialized to
the same value as Null_Bounded_String.
84.
function Length (Source : in Bounded_String) return Length_Range;
a. The Length function returns the length of the string represented by
Source.
1.
function To_Bounded_String (Source : in String;
Drop : in Truncation := Error)
return Bounded_String;
a. If Source'Length <= Max_Length then this function returns a
Bounded_String that represents Source. Otherwise the effect depends
on the value of Drop:
1. If Drop=Left, then the result is a Bounded_String that
represents the string comprising the rightmost Max_Length
characters of Source.
2. If Drop=Right, then the result is a Bounded_String that
represents the string comprising the leftmost Max_Length
characters of Source.
3. If Drop=Error, then Strings.Length_Error is propagated.
1.
function To_String (Source : in Bounded_String) return String;
a. To_String returns the String value with lower bound 1 represented by
Source. If B is a Bounded_String, then B =
To_Bounded_String(To_String(B)).
1. Each of the Append functions returns a Bounded_String obtained by
concatenating the string or character given or represented by one of the
parameters, with the string or character given or represented by the
other parameter, and applying To_Bounded_String to the concatenation
result string, with Drop as provided to the Append function.
2. Each of the procedures Append(Source, New_Item, Drop) has the same effect
as the corresponding assignment Source := Append(Source, New_Item, Drop).
3. Each of the "&" functions has the same effect as the corresponding Append
function, with Error as the Drop parameter.
4.
function Element (Source : in Bounded_String;
Index : in Positive)
return Character;
a. Returns the character at position Index in the string represented by
Source; propagates Index_Error if Index > Length(Source).
1.
procedure Replace_Element (Source : in out Bounded_String;
Index : in Positive;
By : in Character);
a. Updates Source such that the character at position Index in the
string represented by Source is By; propagates Index_Error if Index
> Length(Source).
1.
function Slice (Source : in Bounded_String;
Low : in Positive;
High : in Natural)
return String;
a. Returns the slice at positions Low through High in the string
represented by Source; propagates Index_Error if Low >
Length(Source)+1.
1. Each of the functions "=", "<", ">","<=", and ">=" returns the same
result as the corresponding String operation applied to the String values
given or represented by the two parameters.
2. Each of the search subprograms (Index, Index_Non_Blank, Count,
Find_Token) has the same effect as the corresponding subprogram in
Strings.Fixed applied to the string represented by the Bounded_String
parameter.
3. Each of the Translate subprograms, when applied to a Bounded_String, has
an analogous effect to the corresponding subprogram in Strings.Fixed. For
the Translate function, the translation is applied to the string
represented by the Bounded_String parameter, and the result is converted
(via To_Bounded_String) to a Bounded_String. For the Translate procedure,
the string represented by the Bounded_String parameter after the
translation is given by the Translate function for fixed-length strings
applied to the string represented by the original value of the parameter.
4. Each of the transformation subprograms (Replace_Slice, Insert, Overwrite,
Delete), selector subprograms (Trim, Head, Tail), and constructor
functions ("*") has an effect based on its corresponding subprogram in
Strings.Fixed, and Replicate is based on Fixed."*". For each of these
subprograms, the corresponding fixed-length string subprogram is applied
to the string represented by the Bounded_String parameter.
To_Bounded_String is applied the result string, with Drop (or Error in
the case of Generic_Bounded_Length."*") determining the effect when the
string length exceeds Max_Length.
Implementation Advice
5. Bounded string objects should not be implemented by implicit pointers and
dynamic allocation.
ΓòÉΓòÉΓòÉ 17.4.5. Unbounded-Length String Handling ΓòÉΓòÉΓòÉ
1. The language-defined package Strings.Unbounded provides a private type
Unbounded_String and a set of operations. An object of type
Unbounded_String represents a String whose low bound is 1 and whose
length can vary conceptually between 0 and Natural'Last. The subprograms
for fixed-length string handling are either overloaded directly for
Unbounded_String, or are modified as needed to reflect the flexibility in
length. Since the Unbounded_String type is private, relevant constructor
and selector operations are provided.
Static Semantics
2. The library package Strings.Unbounded has the following declaration:
3.
with Ada.Strings.Maps;
package Ada.Strings.Unbounded is
pragma Preelaborate(Unbounded);
4.
type Unbounded_String is private;
5.
Null_Unbounded_String : constant Unbounded_String;
6.
function Length (Source : in Unbounded_String) return Natural;
7.
type String_Access is access all String;
procedure Free (X : in out String_Access);
8.
-- Conversion, Concatenation, and Selection functions
9.
function To_Unbounded_String (Source : in String)
return Unbounded_String;
10.
function To_Unbounded_String (Length : in Natural)
return Unbounded_String;
11.
function To_String (Source : in Unbounded_String) return String;
12.
procedure Append (Source : in out Unbounded_String;
New_Item : in Unbounded_String);
13.
procedure Append (Source : in out Unbounded_String;
New_Item : in String);
14.
procedure Append (Source : in out Unbounded_String;
New_Item : in Character);
15.
function "&" (Left, Right : in Unbounded_String)
return Unbounded_String;
16.
function "&" (Left : in Unbounded_String; Right : in String)
return Unbounded_String;
17.
function "&" (Left : in String; Right : in Unbounded_String)
return Unbounded_String;
18.
function "&" (Left : in Unbounded_String; Right : in Character)
return Unbounded_String;
19.
function "&" (Left : in Character; Right : in Unbounded_String)
return Unbounded_String;
20.
function Element (Source : in Unbounded_String;
Index : in Positive)
return Character;
21.
procedure Replace_Element (Source : in out Unbounded_String;
Index : in Positive;
By : in Character);
22.
function Slice (Source : in Unbounded_String;
Low : in Positive;
High : in Natural)
return String;
23.
function "=" (Left, Right : in Unbounded_String) return Boolean;
24.
function "=" (Left : in Unbounded_String; Right : in String)
return Boolean;
25.
function "=" (Left : in String; Right : in Unbounded_String)
return Boolean;
26.
function "<" (Left, Right : in Unbounded_String) return Boolean;
27.
function "<" (Left : in Unbounded_String; Right : in String)
return Boolean;
28.
function "<" (Left : in String; Right : in Unbounded_String)
return Boolean;
29.
function "<=" (Left, Right : in Unbounded_String) return Boolean;
30.
function "<=" (Left : in Unbounded_String; Right : in String)
return Boolean;
31.
function "<=" (Left : in String; Right : in Unbounded_String)
return Boolean;
32.
function ">" (Left, Right : in Unbounded_String) return Boolean;
33.
function ">" (Left : in Unbounded_String; Right : in String)
return Boolean;
34.
function ">" (Left : in String; Right : in Unbounded_String)
return Boolean;
35.
function ">=" (Left, Right : in Unbounded_String) return Boolean;
36.
function ">=" (Left : in Unbounded_String; Right : in String)
return Boolean;
37.
function ">=" (Left : in String; Right : in Unbounded_String)
return Boolean;
38.
-- Search subprograms
39.
function Index (Source : in Unbounded_String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
40.
function Index (Source : in Unbounded_String;
Pattern : in String;
Going : in Direction := Forward;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
41.
function Index (Source : in Unbounded_String;
Set : in Maps.Character_Set;
Test : in Membership := Inside;
Going : in Direction := Forward) return Natural;
42.
function Index_Non_Blank (Source : in Unbounded_String;
Going : in Direction := Forward)
return Natural;
43.
function Count (Source : in Unbounded_String;
Pattern : in String;
Mapping : in Maps.Character_Mapping
:= Maps.Identity)
return Natural;
44.
function Count (Source : in Unbounded_String;
Pattern : in String;
Mapping : in Maps.Character_Mapping_Function)
return Natural;
45.
function Count (Source : in Unbounded_String;
Set : in Maps.Character_Set)
return Natural;
46.
procedure Find_Token (Source : in Unbounded_String;
Set : in Maps.Character_Set;
Test : in Membership;
First : out Positive;
Last : out Natural);
47.
-- String translation subprograms
48.
function Translate (Source : in Unbounded_String;
Mapping : in Maps.Character_Mapping)
return Unbounded_String;
49.
procedure Translate (Source : in out Unbounded_String;
Mapping : in Maps.Character_Mapping);
50.
function Translate
(Source : in Unbounded_String;
Mapping : in Maps.Character_Mapping_Function)
return Unbounded_String;
51.
procedure Translate
(Source : in out Unbounded_String;
Mapping : in Maps.Character_Mapping_Function);
52.
-- String transformation subprograms
53.
function Replace_Slice (Source : in Unbounded_String;
Low : in Positive;
High : in Natural;
By : in String)
return Unbounded_String;
54.
procedure Replace_Slice (Source : in out Unbounded_String;
Low : in Positive;
High : in Natural;
By : in String);
55.
function Insert (Source : in Unbounded_String;
Before : in Positive;
New_Item : in String)
return Unbounded_String;
56.
procedure Insert (Source : in out Unbounded_String;
Before : in Positive;
New_Item : in String);
57.
function Overwrite (Source : in Unbounded_String;
Position : in Positive;
New_Item : in String)
return Unbounded_String;
58.
procedure Overwrite (Source : in out Unbounded_String;
Position : in Positive;
New_Item : in String);
59.
function Delete (Source : in Unbounded_String;
From : in Positive;
Through : in Natural)
return Unbounded_String;
60.
procedure Delete (Source : in out Unbounded_String;
From : in Positive;
Through : in Natural);
61.
function Trim (Source : in Unbounded_String;
Side : in Trim_End)
return Unbounded_String;
62.
procedure Trim (Source : in out Unbounded_String;
Side : in Trim_End);
63.
function Trim (Source : in Unbounded_String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set)
return Unbounded_String;
64.
procedure Trim (Source : in out Unbounded_String;
Left : in Maps.Character_Set;
Right : in Maps.Character_Set);
65.
function Head (Source : in Unbounded_String;
Count : in Natural;
Pad : in Character := Space)
return Unbounded_String;
66.
procedure Head (Source : in out Unbounded_String;
Count : in Natural;
Pad : in Character := Space);
67.
function Tail (Source : in Unbounded_String;
Count : in Natural;
Pad : in Character := Space)
return Unbounded_String;
68.
procedure Tail (Source : in out Unbounded_String;
Count : in Natural;
Pad : in Character := Space);
69.
function "*" (Left : in Natural;
Right : in Character)
return Unbounded_String;
70.
function "*" (Left : in Natural;
Right : in String)
return Unbounded_String;
71.
function "*" (Left : in Natural;
Right : in Unbounded_String)
return Unbounded_String;
72.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Strings.Unbounded;
73. Null_Unbounded_String represents the null String. If an object of type
Unbounded_String is not otherwise initialized, it will be initialized to
the same value as Null_Unbounded_String.
74. The function Length returns the length of the String represented by
Source.
75. The type String_Access provides a (non-private) access type for explicit
processing of unbounded-length strings. The procedure Free performs an
unchecked deallocation of an object of type String_Access.
76. The function To_Unbounded_String(Source : in String) returns an
Unbounded_String that represents Source. The function
To_Unbounded_String(Length : in Natural) returns an Unbounded_String that
represents an uninitialized String whose length is Length.
77. The function To_String returns the String with lower bound 1 represented
by Source. To_String and To_Unbounded_String are related as follows:
a. If S is a String, then To_String(To_Unbounded_String(S)) = S.
b. If U is an Unbounded_String, then To_Unbounded_String(To_String(U))
= U.
1. For each of the Append procedures, the resulting string represented by
the Source parameter is given by the concatenation of the original value
of Source and the value of New_Item.
2. Each of the "&" functions returns an Unbounded_String obtained by
concatenating the string or character given or represented by one of the
parameters, with the string or character given or represented by the
other parameter, and applying To_Unbounded_String to the concatenation
result string.
3. The Element, Replace_Element, and Slice subprograms have the same effect
as the corresponding bounded-length string subprograms.
4. Each of the functions "=", "<", ">","<=", and ">=" returns the same
result as the corresponding String operation applied to the String values
given or represented by Left and Right.
5. Each of the search subprograms (Index, Index_Non_Blank, Count,
Find_Token) has the same effect as the corresponding subprogram in
Strings.Fixed applied to the string represented by the Unbounded_String
parameter.
6. The Translate function has an analogous effect to the corresponding
subprogram in Strings.Fixed. The translation is applied to the string
represented by the Unbounded_String parameter, and the result is
converted (via To_Unbounded_String) to an Unbounded_String.
7. Each of the transformation functions (Replace_Slice, Insert, Overwrite,
Delete), selector functions (Trim, Head, Tail), and constructor functions
("*") is likewise analogous to its corresponding subprogram in
Strings.Fixed. For each of the subprograms, the corresponding
fixed-length string subprogram is applied to the string represented by
the Unbounded_String parameter, and To_Unbounded_String is applied the
result string.
8. For each of the procedures Translate, Replace_Slice, Insert, Overwrite,
Delete, Trim, Head, and Tail, the resulting string represented by the
Source parameter is given by the corresponding function for fixed-length
strings applied to the string represented by Source's original value.
Implementation Requirements
9. No storage associated with an Unbounded_String object shall be lost upon
assignment or scope exit.
ΓòÉΓòÉΓòÉ 17.4.6. String-Handling Sets and Mappings ΓòÉΓòÉΓòÉ
1. The language-defined package Strings.Maps.Constants declares
Character_Set and Character_Mapping constants corresponding to
classification and conversion functions in package Characters.Handling.
Static Semantics
2. The library package Strings.Maps.Constants has the following declaration:
3.
package Ada.Strings.Maps.Constants is
pragma Preelaborate(Constants);
4.
Control_Set : constant Character_Set;
Graphic_Set : constant Character_Set;
Letter_Set : constant Character_Set;
Lower_Set : constant Character_Set;
Upper_Set : constant Character_Set;
Basic_Set : constant Character_Set;
Decimal_Digit_Set : constant Character_Set;
Hexadecimal_Digit_Set : constant Character_Set;
Alphanumeric_Set : constant Character_Set;
Special_Set : constant Character_Set;
ISO_646_Set : constant Character_Set;
5.
Lower_Case_Map : constant Character_Mapping;
--Maps to lower case for letters, else identity
Upper_Case_Map : constant Character_Mapping;
--Maps to upper case for letters, else identity
Basic_Map : constant Character_Mapping;
--Maps to basic letter for letters, else identity
6.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Strings.Maps.Constants;
7. Each of these constants represents a correspondingly named set of
characters or character mapping in Characters.Handling, see A.3.2.
ΓòÉΓòÉΓòÉ 17.4.7. Wide_String Handling ΓòÉΓòÉΓòÉ
1. Facilities for handling strings of Wide_Character elements are found in
the packages Strings.Wide_Maps, Strings.Wide_Fixed, Strings.Wide_Bounded,
Strings.Wide_Unbounded, and Strings.Wide_Maps.Wide_Constants. They
provide the same string-handling operations as the corresponding packages
for strings of Character elements.
Static Semantics
2. The package Strings.Wide_Maps has the following declaration.
3.
package Ada.Strings.Wide_Maps is
pragma Preelaborate(Wide_Maps);
4.
-- Representation for a set of Wide_Character values:
type Wide_Character_Set is private;
5.
Null_Set : constant Wide_Character_Set;
6.
type Wide_Character_Range is
record
Low : Wide_Character;
High : Wide_Character;
end record;
-- Represents Wide_Character range Low┬╖┬╖High
7.
type Wide_Character_Ranges is array (Positive range <>)
of Wide_Character_Range;
8.
function To_Set (Ranges : in Wide_Character_Ranges)
return Wide_Character_Set;
9.
function To_Set (Span : in Wide_Character_Range)
return Wide_Character_Set;
10.
function To_Ranges (Set : in Wide_Character_Set)
return Wide_Character_Ranges;
11.
function "=" (Left, Right : in Wide_Character_Set) return Boolean;
12.
function "not" (Right : in Wide_Character_Set)
return Wide_Character_Set;
function "and" (Left, Right : in Wide_Character_Set)
return Wide_Character_Set;
function "or" (Left, Right : in Wide_Character_Set)
return Wide_Character_Set;
function "xor" (Left, Right : in Wide_Character_Set)
return Wide_Character_Set;
function "-" (Left, Right : in Wide_Character_Set)
return Wide_Character_Set;
13.
function Is_In (Element : in Wide_Character;
Set : in Wide_Character_Set)
return Boolean;
14.
function Is_Subset (Elements : in Wide_Character_Set;
Set : in Wide_Character_Set)
return Boolean;
15.
function "<=" (Left : in Wide_Character_Set;
Right : in Wide_Character_Set)
return Boolean renames Is_Subset;
16.
-- Alternative representation for a set of Wide_Character values:
subtype Wide_Character_Sequence is Wide_String;
17.
function To_Set (Sequence : in Wide_Character_Sequence)
return Wide_Character_Set;
18.
function To_Set (Singleton : in Wide_Character)
return Wide_Character_Set;
19.
function To_Sequence (Set : in Wide_Character_Set)
return Wide_Character_Sequence;
20.
-- Representation for a Wide_Character to Wide_Character mapping:
type Wide_Character_Mapping is private;
21.
function Value (Map : in Wide_Character_Mapping;
Element : in Wide_Character)
return Wide_Character;
22.
Identity : constant Wide_Character_Mapping;
23.
function To_Mapping (From, To : in Wide_Character_Sequence)
return Wide_Character_Mapping;
24.
function To_Domain (Map : in Wide_Character_Mapping)
return Wide_Character_Sequence;
25.
function To_Range (Map : in Wide_Character_Mapping)
return Wide_Character_Sequence;
26.
type Wide_Character_Mapping_Function is access
function (From : in Wide_Character) return Wide_Character;
27.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Strings.Wide_Maps;
28. The context clause for each of the packages Strings.Wide_Fixed,
Strings.Wide_Bounded, and Strings.Wide_Unbounded identifies
Strings.Wide_Maps instead of Strings.Maps.
29. For each of the packages Strings.Fixed, Strings.Bounded,
Strings.Unbounded, and Strings.Maps.Constants the corresponding wide
string package has the same contents except that
a. Wide_Space replaces Space
b. Wide_Character replaces Character
c. Wide_String replaces String
d. Wide_Character_Set replaces Character_Set
e. Wide_Character_Mapping replaces Character_Mapping
f. Wide_Character_Mapping_Function replaces Character_Mapping_Function
g. Wide_Maps replaces Maps
h. Bounded_Wide_String replaces Bounded_String
i. Null_Bounded_Wide_String replaces Null_Bounded_String
j. To_Bounded_Wide_String replaces To_Bounded_String
k. To_Wide_String replaces To_String
l. Unbounded_Wide_String replaces Unbounded_String
m. Null_Unbounded_Wide_String replaces Null_Unbounded_String
n. Wide_String_Access replaces String_Access
o. To_Unbounded_Wide_String replaces To_Unbounded_String
1. The following additional declaration is present in
Strings.Wide_Maps.Wide_Constants:
2.
Character_Set : constant Wide_Maps.Wide_Character_Set;
-- Contains each Wide_Character value WC such that
-- Characters.Is_Character(WC) is True
NOTES
3. (12) If a null Wide_Character_Mapping_Function is passed to any of the
Wide_String handling subprograms, Constraint_Error is propagated.
4. (13) Each Wide_Character_Set constant in the package
Strings.Wide_Maps.Wide_Constants contains no values outside the Character
portion of Wide_Character. Similarly, each Wide_Character_Mapping
constant in this package is the identity mapping when applied to any
element outside the Character portion of Wide_Character.
ΓòÉΓòÉΓòÉ 17.5. The Numerics Packages ΓòÉΓòÉΓòÉ
1. The library package Numerics is the parent of several child units that
provide facilities for mathematical computation. One child, the generic
package Generic_Elementary_Functions, is defined in A.5.1, together with
nongeneric equivalents; two others, the package Float_Random and the
generic package Discrete_Random, are defined in A.5.2. Additional
(optional) children are defined in G: ``Numerics''.
Static Semantics
1.
package Ada.Numerics is
pragma Pure(Numerics);
Argument_Error : exception;
Pi : constant :=
3.14159_26535_89793_23846_26433_83279_50288_41971_69399_37511;
e : constant :=
2.71828_18284_59045_23536_02874_71352_66249_77572_47093_69996;
end Ada.Numerics;
2. The Argument_Error exception is raised by a subprogram in a child unit of
Numerics to signal that one or more of the actual subprogram parameters
are outside the domain of the corresponding mathematical function.
Implementation Permissions
3. The implementation may specify the values of Pi and e to a larger number
of significant digits.
A.5.1 Elementary Functions
A.5.2 Random Number Generation
A.5.3 Attributes of Floating Point Types
A.5.4 Attributes of Fixed Point Types
ΓòÉΓòÉΓòÉ 17.5.1. Elementary Functions ΓòÉΓòÉΓòÉ
1. Implementation-defined approximations to the mathematical functions known
as the ``elementary functions'' are provided by the subprograms in
Numerics.Generic_Elementary_Functions. Nongeneric equivalents of this
generic package for each of the predefined floating point types are also
provided as children of Numerics.
Static Semantics
2. The generic library package Numerics.Generic_Elementary_Functions has the
following declaration:
3.
generic
type Float_Type is digits <>;
package Ada.Numerics.Generic_Elementary_Functions is
pragma Pure(Generic_Elementary_Functions);
4.
function Sqrt (X : Float_Type'Base) return Float_Type'Base;
function Log (X : Float_Type'Base) return Float_Type'Base;
function Log (X, Base : Float_Type'Base) return Float_Type'Base;
function Exp (X : Float_Type'Base) return Float_Type'Base;
function "**" (Left, Right : Float_Type'Base)
return Float_Type'Base;
5.
function Sin (X : Float_Type'Base) return Float_Type'Base;
function Sin (X, Cycle : Float_Type'Base) return Float_Type'Base;
function Cos (X : Float_Type'Base) return Float_Type'Base;
function Cos (X, Cycle : Float_Type'Base) return Float_Type'Base;
function Tan (X : Float_Type'Base) return Float_Type'Base;
function Tan (X, Cycle : Float_Type'Base) return Float_Type'Base;
function Cot (X : Float_Type'Base) return Float_Type'Base;
function Cot (X, Cycle : Float_Type'Base) return Float_Type'Base;
6.
function Arcsin (X : Float_Type'Base)
return Float_Type'Base;
function Arcsin (X, Cycle : Float_Type'Base)
return Float_Type'Base;
function Arccos (X : Float_Type'Base)
return Float_Type'Base;
function Arccos (X, Cycle : Float_Type'Base)
return Float_Type'Base;
function Arctan (Y : Float_Type'Base;
X : Float_Type'Base := 1.0)
return Float_Type'Base;
function Arctan (Y : Float_Type'Base;
X : Float_Type'Base := 1.0;
Cycle : Float_Type'Base)
return Float_Type'Base;
function Arccot (X : Float_Type'Base;
Y : Float_Type'Base := 1.0)
return Float_Type'Base;
function Arccot (X : Float_Type'Base;
Y : Float_Type'Base := 1.0;
Cycle : Float_Type'Base)
return Float_Type'Base;
7.
function Sinh (X : Float_Type'Base) return Float_Type'Base;
function Cosh (X : Float_Type'Base) return Float_Type'Base;
function Tanh (X : Float_Type'Base) return Float_Type'Base;
function Coth (X : Float_Type'Base) return Float_Type'Base;
function Arcsinh (X : Float_Type'Base) return Float_Type'Base;
function Arccosh (X : Float_Type'Base) return Float_Type'Base;
function Arctanh (X : Float_Type'Base) return Float_Type'Base;
function Arccoth (X : Float_Type'Base) return Float_Type'Base;
8.
end Ada.Numerics.Generic_Elementary_Functions;
9. The library package Numerics.Elementary_Functions defines the same
subprograms as Numerics.Generic_Elementary_Functions, except that the
predefined type Float is systematically substituted for Float_Type'Base
throughout. Nongeneric equivalents of
Numerics.Generic_Elementary_Functions for each of the other predefined
floating point types are defined similarly, with the names
Numerics.Short_Elementary_Functions, Numerics.Long_Elementary_Functions,
etc.
10. The functions have their usual mathematical meanings. When the Base
parameter is specified, the Log function computes the logarithm to the
given base; otherwise, it computes the natural logarithm. When the Cycle
parameter is specified, the parameter X of the forward trigonometric
functions (Sin, Cos, Tan, and Cot) and the results of the inverse
trigonometric functions (Arcsin, Arccos, Arctan, and Arccot) are measured
in units such that a full cycle of revolution has the given value;
otherwise, they are measured in radians.
11. The computed results of the mathematically multivalued functions are
rendered single-valued by the following conventions, which are meant to
imply the principal branch:
a. The results of the Sqrt and Arccosh functions and that of the
exponentiation operator are nonnegative.
b. The result of the Arcsin function is in the quadrant containing the
point (1.0, x), where x is the value of the parameter X. This
quadrant is I or IV; thus, the range of the Arcsin function is
approximately -Pi/2.0 to Pi/2.0 (-Cycle/4.0 to Cycle/4.0, if the
parameter Cycle is specified).
c. The result of the Arccos function is in the quadrant containing the
point (x, 1.0), where x is the value of the parameter X. This
quadrant is I or II; thus, the Arccos function ranges from 0.0 to
approximately Pi (Cycle/2.0, if the parameter Cycle is specified).
d. The results of the Arctan and Arccot functions are in the quadrant
containing the point (x, y), where x and y are the values of the
parameters X and Y, respectively. This may be any quadrant (I
through IV) when the parameter X (resp., Y) of Arctan (resp.,
Arccot) is specified, but it is restricted to quadrants I and IV
(resp., I and II) when that parameter is omitted. Thus, the range
when that parameter is specified is approximately -Pi to Pi
(-Cycle/2.0 to Cycle/2.0, if the parameter Cycle is specified); when
omitted, the range of Arctan (resp., Arccot) is that of Arcsin
(resp., Arccos), as given above. When the point (x, y) lies on the
negative x-axis, the result approximates
1. Pi (resp., -Pi) when the sign of the parameter Y is positive
(resp., negative), if Float_Type'Signed_Zeros is True;
2. Pi, if Float_Type'Signed_Zeros is False.
1. (In the case of the inverse trigonometric functions, in which a result
lying on or near one of the axes may not be exactly representable, the
approximation inherent in computing the result may place it in an
adjacent quadrant, close to but on the wrong side of the axis.)
Dynamic Semantics
2. The exception Numerics.Argument_Error is raised, signaling a parameter
value outside the domain of the corresponding mathematical function, in
the following cases:
a. by any forward or inverse trigonometric function with specified
cycle, when the value of the parameter Cycle is zero or negative;
b. by the Log function with specified base, when the value of the
parameter Base is zero, one, or negative;
c. by the Sqrt and Log functions, when the value of the parameter X is
negative;
d. by the exponentiation operator, when the value of the left operand
is negative or when both operands have the value zero;
e. by the Arcsin, Arccos, and Arctanh functions, when the absolute
value of the parameter X exceeds one;
f. by the Arctan and Arccot functions, when the parameters X and Y both
have the value zero;
g. by the Arccosh function, when the value of the parameter X is less
than one; and
h. by the Arccoth function, when the absolute value of the parameter X
is less than one.
1. The exception Constraint_Error is raised, signaling a pole of the
mathematical function (analogous to dividing by zero), in the following
cases, provided that Float_Type'Machine_Overflows is True:
a. by the Log, Cot, and Coth functions, when the value of the parameter
X is zero;
b. by the exponentiation operator, when the value of the left operand
is zero and the value of the exponent is negative;
c. by the Tan function with specified cycle, when the value of the
parameter X is an odd multiple of the quarter cycle;
d. by the Cot function with specified cycle, when the value of the
parameter X is zero or a multiple of the half cycle; and
e. by the Arctanh and Arccoth functions, when the absolute value of the
parameter X is one.
1. Constraint_Error can also be raised when a finite result overflows (see
G.2.4) this may occur for parameter values sufficiently near poles, and,
in the case of some of the functions, for parameter values with
sufficiently large magnitudes. When Float_Type'Machine_Overflows is
False, the result at poles is unspecified.
2. When one parameter of a function with multiple parameters represents a
pole and another is outside the function's domain, the latter takes
precedence (i.e., Numerics.Argument_Error is raised).
Implementation Requirements
3. In the implementation of Numerics.Generic_Elementary_Functions, the range
of intermediate values allowed during the calculation of a final result
shall not be affected by any range constraint of the subtype Float_Type.
4. In the following cases, evaluation of an elementary function shall yield
the prescribed result, provided that the preceding rules do not call for
an exception to be raised:
a. When the parameter X has the value zero, the Sqrt, Sin, Arcsin, Tan,
Sinh, Arcsinh, Tanh, and Arctanh functions yield a result of zero,
and the Exp, Cos, and Cosh functions yield a result of one.
b. When the parameter X has the value one, the Sqrt function yields a
result of one, and the Log, Arccos, and Arccosh functions yield a
result of zero.
c. When the parameter Y has the value zero and the parameter X has a
positive value, the Arctan and Arccot functions yield a result of
zero.
d. The results of the Sin, Cos, Tan, and Cot functions with specified
cycle are exact when the mathematical result is zero; those of the
first two are also exact when the mathematical result is +/-1.0.
e. Exponentiation by a zero exponent yields the value one.
Exponentiation by a unit exponent yields the value of the left
operand. Exponentiation of the value one yields the value one.
Exponentiation of the value zero yields the value zero.
1. Other accuracy requirements for the elementary functions, which apply
only in implementations conforming to the Numerics Annex, and then only
in the ``strict'' mode defined there, see G.2, are given in G.2.4.
2. When Float_Type'Signed_Zeros is True, the sign of a zero result shall be
as follows:
a. A prescribed zero result delivered at the origin by one of the odd
functions (Sin, Arcsin, Sinh, Arcsinh, Tan, Arctan or Arccot as a
function of Y when X is fixed and positive, Tanh, and Arctanh) has
the sign of the parameter X (Y, in the case of Arctan or Arccot).
b. A prescribed zero result delivered by one of the odd functions away
from the origin, or by some other elementary function, has an
implementation-defined sign.
c. A zero result that is not a prescribed result (i.e., one that
results from rounding or underflow) has the correct mathematical
sign.
Implementation Permissions
1. The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined
type.
ΓòÉΓòÉΓòÉ 17.5.2. Random Number Generation ΓòÉΓòÉΓòÉ
1. Facilities for the generation of pseudo-random floating point numbers are
provided in the package Numerics.Float_Random; the generic package
Numerics.Discrete_Random provides similar facilities for the generation
of pseudo-random integers and pseudo-random values of enumeration types.
For brevity, pseudo-random values of any of these types are called random
numbers.
2. Some of the facilities provided are basic to all applications of random
numbers. These include a limited private type each of whose objects
serves as the generator of a (possibly distinct) sequence of random
numbers; a function to obtain the ``next'' random number from a given
sequence of random numbers (that is, from its generator); and subprograms
to initialize or reinitialize a given generator to a time-dependent state
or a state denoted by a single integer.
3. Other facilities are provided specifically for advanced applications.
These include subprograms to save and restore the state of a given
generator; a private type whose objects can be used to hold the saved
state of a generator; and subprograms to obtain a string representation
of a given generator state, or, given such a string representation, the
corresponding state.
Static Semantics
4. The library package Numerics.Float_Random has the following declaration:
5.
package Ada.Numerics.Float_Random is
6.
-- Basic facilities
7.
type Generator is limited private;
8.
subtype Uniformly_Distributed is Float range 0.0 ┬╖┬╖ 1.0;
function Random (Gen : Generator) return Uniformly_Distributed;
9.
procedure Reset (Gen : in Generator;
Initiator : in Integer);
procedure Reset (Gen : in Generator);
10.
-- Advanced facilities
11.
type State is private;
12.
procedure Save (Gen : in Generator;
To_State : out State);
procedure Reset (Gen : in Generator;
From_State : in State);
13.
Max_Image_Width : constant
:= implementation-defined integer value;
14.
function Image (Of_State : State) return String;
function Value (Coded_State : String) return State;
15.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Numerics.Float_Random;
16. The generic library package Numerics.Discrete_Random has the following
declaration:
17.
generic
type Result_Subtype is (<>);
package Ada.Numerics.Discrete_Random is
18.
-- Basic facilities
19.
type Generator is limited private;
20.
function Random (Gen : Generator) return Result_Subtype;
21.
procedure Reset (Gen : in Generator;
Initiator : in Integer);
procedure Reset (Gen : in Generator);
22.
-- Advanced facilities
23.
type State is private;
24.
procedure Save (Gen : in Generator;
To_State : out State);
procedure Reset (Gen : in Generator;
From_State : in State);
25.
Max_Image_Width : constant
:= implementation-defined integer value;
26.
function Image (Of_State : State) return String;
function Value (Coded_State : String) return State;
27.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Numerics.Discrete_Random;
28. An object of the limited private type Generator is associated with a
sequence of random numbers. Each generator has a hidden (internal) state,
which the operations on generators use to determine the position in the
associated sequence. All generators are implicitly initialized to an
unspecified state that does not vary from one program execution to
another; they may also be explicitly initialized, or reinitialized, to a
time-dependent state, to a previously saved state, or to a state uniquely
denoted by an integer value.
29. An object of the private type State can be used to hold the internal
state of a generator. Such objects are only needed if the application is
designed to save and restore generator states or to examine or
manufacture them.
30. The operations on generators affect the state and therefore the future
values of the associated sequence. The semantics of the operations on
generators and states are defined below.
31.
function Random (Gen : Generator) return Uniformly_Distributed;
function Random (Gen : Generator) return Result_Subtype;
a. Obtains the ``next'' random number from the given generator,
relative to its current state, according to an
implementation-defined algorithm. The result of the function in
Numerics.Float_Random is delivered as a value of the subtype
Uniformly_Distributed, which is a subtype of the predefined type
Float having a range of 0.0 ┬╖┬╖ 1.0. The result of the function in an
instantiation of Numerics.Discrete_Random is delivered as a value of
the generic formal subtype Result_Subtype.
1.
procedure Reset (Gen : in Generator;
Initiator : in Integer);
procedure Reset (Gen : in Generator);
a. Sets the state of the specified generator to one that is an
unspecified function of the value of the parameter Initiator (or to
a time-dependent state, if only a generator parameter is specified).
The latter form of the procedure is known as the time-dependent
Reset procedure.
1.
procedure Save (Gen : in Generator;
To_State : out State);
procedure Reset (Gen : in Generator;
From_State : in State);
a. Save obtains the current state of a generator. Reset gives a
generator the specified state. A generator that is reset to a state
previously obtained by invoking Save is restored to the state it had
when Save was invoked.
1.
function Image (Of_State : State) return String;
function Value (Coded_State : String) return State;
a. Image provides a representation of a state coded (in an
implementation-defined way) as a string whose length is bounded by
the value of Max_Image_Width. Value is the inverse of Image:
Value(Image(S)) = S for each state S that can be obtained from a
generator by invoking Save.
Dynamic Semantics
1. Instantiation of Numerics.Discrete_Random with a subtype having a null
range raises Constraint_Error.
2. Invoking Value with a string that is not the image of any generator state
raises Constraint_Error.
Implementation Requirements
3. A sufficiently long sequence of random numbers obtained by successive
calls to Random is approximately uniformly distributed over the range of
the result subtype.
4. The Random function in an instantiation of Numerics.Discrete_Random is
guaranteed to yield each value in its result subtype in a finite number
of calls, provided that the number of such values does not exceed 2 **
15.
5. Other performance requirements for the random number generator, which
apply only in implementations conforming to the Numerics Annex, and then
only in the ``strict'' mode defined there, see G.2, are given in G.2.5.
Documentation Requirements
6. No one algorithm for random number generation is best for all
applications. To enable the user to determine the suitability of the
random number generators for the intended application, the implementation
shall describe the algorithm used and shall give its period, if known
exactly, or a lower bound on the period, if the exact period is unknown.
Periods that are so long that the periodicity is unobservable in practice
can be described in such terms, without giving a numerical bound.
7. The implementation also shall document the minimum time interval between
calls to the time-dependent Reset procedure that are guaranteed to
initiate different sequences, and it shall document the nature of the
strings that Value will accept without raising Constraint_Error.
Implementation Advice
8. Any storage associated with an object of type Generator should be
reclaimed on exit from the scope of the object.
9. If the generator period is sufficiently long in relation to the number of
distinct initiator values, then each possible value of Initiator passed
to Reset should initiate a sequence of random numbers that does not, in a
practical sense, overlap the sequence initiated by any other value. If
this is not possible, then the mapping between initiator values and
generator states should be a rapidly varying function of the initiator
value.
NOTES
10. (14) If two or more tasks are to share the same generator, then the tasks
have to synchronize their access to the generator as for any shared
variable, see 9.10.
11. (15) Within a given implementation, a repeatable random number sequence
can be obtained by relying on the implicit initialization of generators
or by explicitly initializing a generator with a repeatable initiator
value. Different sequences of random numbers can be obtained from a given
generator in different program executions by explicitly initializing the
generator to a time-dependent state.
12. (16) A given implementation of the Random function in
Numerics.Float_Random may or may not be capable of delivering the values
0.0 or 1.0. Portable applications should assume that these values, or
values sufficiently close to them to behave indistinguishably from them,
can occur. If a sequence of random integers from some fixed range is
needed, the application should use the Random function in an appropriate
instantiation of Numerics.Discrete_Random, rather than transforming the
result of the Random function in Numerics.Float_Random. However, some
applications with unusual requirements, such as for a sequence of random
integers each drawn from a different range, will find it more convenient
to transform the result of the floating point Random function. For M>=1,
the expression
13.
Integer(Float(M) * Random(G)) mod M
14. transforms the result of Random(G) to an integer uniformly distributed
over the range 0 ┬╖┬╖ M-1; it is valid even if Random delivers 0.0 or 1.0.
Each value of the result range is possible, provided that M is not too
large. Exponentially distributed (floating point) random numbers with
mean and standard deviation 1.0 can be obtained by the transformation
15.
-Log(Random(G) + Float'Model_Small))
16. where Log comes from Numerics.Elementary_Functions, see A.5.1, in this
expression, the addition of Float'Model_Small avoids the exception that
would be raised were Log to be given the value zero, without affecting
the result (in most implementations) when Random returns a nonzero value.
Examples
17. Example of a program that plays a simulated dice game:
18.
with Ada.Numerics.Discrete_Random;
procedure Dice_Game is
subtype Die is Integer range 1 ┬╖┬╖ 6;
subtype Dice is Integer range 2*Die'First ┬╖┬╖ 2*Die'Last;
package Random_Die is new Ada.Numerics.Discrete_Random (Die);
use Random_Die;
G : Generator;
D : Dice;
begin
Reset (G); -- Start the generator in a unique state in each run
loop
-- Roll a pair of dice; sum and process the results
D := Random(G) + Random(G);
┬╖┬╖┬╖
end loop;
end Dice_Game;
19. Example of a program that simulates coin tosses:
20.
with Ada.Numerics.Discrete_Random;
procedure Flip_A_Coin is
type Coin is (Heads, Tails);
package Random_Coin is new Ada.Numerics.Discrete_Random (Coin);
use Random_Coin;
G : Generator;
begin
Reset (G); -- Start the generator in a unique state in each run
loop
-- Toss a coin and process the result
case Random(G) is
when Heads =>
┬╖┬╖┬╖
when Tails =>
┬╖┬╖┬╖
end case;
┬╖┬╖┬╖
end loop;
end Flip_A_Coin;
21. Example of a parallel simulation of a physical system, with a separate
generator of event probabilities in each task:
22.
with Ada.Numerics.Float_Random;
procedure Parallel_Simulation is
use Ada.Numerics.Float_Random;
task type Worker is
entry Initialize_Generator (Initiator : in Integer);
┬╖┬╖┬╖
end Worker;
W : array (1 ┬╖┬╖ 10) of Worker;
task body Worker is
G : Generator;
Probability_Of_Event : Uniformly_Distributed;
begin
accept Initialize_Generator (Initiator : in Integer) do
Reset (G, Initiator);
end Initialize_Generator;
loop
┬╖┬╖┬╖
Probability_Of_Event := Random(G);
┬╖┬╖┬╖
end loop;
end Worker;
begin
-- Initialize the generators in the Worker tasks
-- to different states
for I in W'Range loop
W(I).Initialize_Generator (I);
end loop;
┬╖┬╖┬╖ -- Wait for the Worker tasks to terminate
end Parallel_Simulation;
NOTES
23. (17) Notes on the last example: Although each Worker task initializes
its generator to a different state, those states will be the same in
every execution of the program. The generator states can be initialized
uniquely in each program execution by instantiating
Ada.Numerics.Discrete_Random for the type Integer in the main procedure,
resetting the generator obtained from that instance to a time-dependent
state, and then using random integers obtained from that generator to
initialize the generators in each Worker task.
ΓòÉΓòÉΓòÉ 17.5.3. Attributes of Floating Point Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The following representation-oriented attributes are defined for every
subtype S of a floating point type T.
2. S'Machine_Radix
Yields the radix of the hardware representation of the type
T. The value of this attribute is of the type universal_integer.
3. The values of other representation-oriented attributes of a floating
point subtype, and of the ``primitive function'' attributes of a floating
point subtype described later, are defined in terms of a particular
representation of nonzero values called the canonical form. The canonical
form (for the type T) is the form
+/-mantissa*T'Machine_Radix ** exponent
where
a. mantissa is a fraction in the number base T'Machine_Radix, the first
digit of which is nonzero, and
b. exponent is an integer.
1. S'Machine_Mantissa
Yields the largest value of p such that every value
expressible in the canonical form (for the type T), having a
p-digit mantissa and an exponent between T'Machine_Emin and
T'Machine_Emax, is a machine number, see 3.5.7, of the type
T. This attribute yields a value of the type
universal_integer.
2. S'Machine_Emin
Yields the smallest (most negative) value of exponent such
that every value expressible in the canonical form (for the
type T), having a mantissa of T'Machine_Mantissa digits, is a
machine number, see 3.5.7, of the type T. This attribute
yields a value of the type universal_integer.
3. S'Machine_Emax
Yields the largest (most positive) value of exponent such
that every value expressible in the canonical form (for the
type T), having a mantissa of T'Machine_Mantissa digits, is a
machine number (see 3.5.7) of the type T. This attribute
yields a value of the type universal_integer.
4. S'Denorm
Yields the value True if every value expressible in the form
+/-mantissa*T'Machine_Radix ** T'Machine_Emin
where mantissa is a nonzero T'Machine_Mantissa-digit fraction
in the number base T'Machine_Radix, the first digit of which
is zero, is a machine number, see 3.5.7, of the type T;
yields the value False otherwise. The value of this
attribute is of the predefined type Boolean.
5. The values described by the formula in the definition of S'Denorm are
called denormalized numbers. A nonzero machine number that is not a
denormalized number is a normalized number. A normalized number x of a
given type T is said to be represented in canonical form when it is
expressed in the canonical form (for the type T) with a mantissa having
T'Machine_Mantissa digits; the resulting form is the canonical-form
representation of x.
6. S'Machine_Rounds
Yields the value True if rounding is performed on inexact
results of every predefined operation that yields a result of
the type T; yields the value False otherwise. The value of
this attribute is of the predefined type Boolean.
7. S'Machine_Overflows
Yields the value True if overflow and divide-by-zero are
detected and reported by raising Constraint_Error for every
predefined operation that yields a result of the type T;
yields the value False otherwise. The value of this
attribute is of the predefined type Boolean.
8. S'Signed_Zeros
Yields the value True if the hardware representation for the
type T has the capability of representing both positively and
negatively signed zeros, these being generated and used by
the predefined operations of the type T as specified in IEC
559:1989; yields the value False otherwise. The value of
this attribute is of the predefined type Boolean.
9. For every value x of a floating point type T, the normalized exponent of
x is defined as follows:
a. the normalized exponent of zero is (by convention) zero;
b. for nonzero x, the normalized exponent of x is the unique integer k
such that T'Machine_Radix ** (k - 1) <=|x|<T'Machine_Radix ** k.
1. The following primitive function attributes are defined for any subtype S
of a floating point type T.
2. S'Exponent
S'Exponent denotes a function with the following specification:
a.
function S'Exponent (X : T)
return universal_integer
b. The function yields the normalized exponent of X.
1. S'Fraction
S'Fraction denotes a function with the following specification:
a.
function S'Fraction (X : T)
return T
b. The function yields the value X*T'Machine_Radix ** -k, where k is
the normalized exponent of X. A zero result, which can only occur
when X is zero, has the sign of X.
1. S'Compose
S'Compose denotes a function with the following specification:
a.
function S'Compose (Fraction : T;
Exponent : universal_integer)
return T
b. Let v be the value Fraction*T'Machine_Radix ** (Exponent-k), where k
is the normalized exponent of Fraction. If v is a machine number of
the type T, or if |v|>=T'Model_Small, the function yields v;
otherwise, it yields either one of the machine numbers of the type T
adjacent to v. Constraint_Error is optionally raised if v is outside
the base range of S. A zero result has the sign of Fraction when
S'Signed_Zeros is True.
1. S'Scaling
a.
S'Scaling denotes a function with the following specification:
b.
function S'Scaling (X : T;
Adjustment : universal_integer)
return T
c. Let v be the value X*T'Machine_Radix ** (Adjustment). If v is a
machine number of the type T, or if |v|>=T'Model_Small, the function
yields v; otherwise, it yields either one of the machine numbers of
the type T adjacent to v. Constraint_Error is optionally raised if v
is outside the base range of S. A zero result has the sign of X when
S'Signed_Zeros is True.
1. S'Floor
S'Floor denotes a function with the following specification:
a.
function S'Floor (X : T)
return T
b. The function yields the value Floor(X), i.e., the largest (most
positive) integral value less than or equal to X. When X is zero,
the result has the sign of X; a zero result otherwise has a positive
sign.
1. S'Ceiling
S'Ceiling denotes a function with the following specification:
a.
function S'Ceiling (X : T)
return T
b. The function yields the value Ceiling(X), i.e., the smallest (most
negative) integral value greater than or equal to X. When X is zero,
the result has the sign of X; a zero result otherwise has a negative
sign when S'Signed_Zeros is True.
1. S'Rounding
S'Rounding denotes a function with the following specification:
a.
function S'Rounding (X : T)
return T
b. The function yields the integral value nearest to X, rounding away
from zero if X lies exactly halfway between two integers. A zero
result has the sign of X when S'Signed_Zeros is True.
1. S'Unbiased_Rounding
S'Unbiased_Rounding denotes a function with the following
specification:
a.
function S'Unbiased_Rounding (X : T)
return T
b. The function yields the integral value nearest to X, rounding toward
the even integer if X lies exactly halfway between two integers. A
zero result has the sign of X when S'Signed_Zeros is True.
1. S'Truncation
S'Truncation denotes a function with the following
specification:
a.
function S'Truncation (X : T)
return T
b. The function yields the value Ceiling(X) when X is negative, and
Floor(X) otherwise. A zero result has the sign of X when
S'Signed_Zeros is True.
1. S'Remainder
S'Remainder denotes a function with the following
specification:
a.
function S'Remainder (X, Y : T)
return T
b. For nonzero Y, let v be the value X-n*Y, where n is the integer
nearest to the exact value of X/Y; if |n-X/Y|=1/2, then n is chosen
to be even. If v is a machine number of the type T, the function
yields v; otherwise, it yields zero. Constraint_Error is raised if Y
is zero. A zero result has the sign of X when S'Signed_Zeros is
True.
1. S'Adjacent
S'Adjacent denotes a function with the following specification:
a.
function S'Adjacent (X, Towards : T)
return T
b. If Towards=X, the function yields X; otherwise, it yields the
machine number of the type T adjacent to X in the direction of
Towards, if that machine number exists. If the result would be
outside the base range of S, Constraint_Error is raised. When
T'Signed_Zeros is True, a zero result has the sign of X. When
Towards is zero, its sign has no bearing on the result.
1. S'Copy_Sign
S'Copy_Sign denotes a function with the following
specification:
a.
function S'Copy_Sign (Value, Sign : T)
return T
b. If the value of Value is nonzero, the function yields a result whose
magnitude is that of Value and whose sign is that of Sign;
otherwise, it yields the value zero. Constraint_Error is optionally
raised if the result is outside the base range of S. A zero result
has the sign of Sign when S'Signed_Zeros is True.
1. S'Leading_Part
S'Leading_Part denotes a function with the following
specification:
a.
function S'Leading_Part (X : T;
Radix_Digits : universal_integer)
return T
b. Let v be the value T'Machine_Radix ** (k-Radix_Digits), where k is
the normalized exponent of X. The function yields the value
1. Floor(X/v)*v, when X is nonnegative and Radix_Digits is
positive;
2. Ceiling(X/v)*v, when X is negative and Radix_Digits is
positive.
a. Constraint_Error is raised when Radix_Digits is zero or negative. A
zero result, which can only occur when X is zero, has the sign of X.
1. S'Machine
S'Machine denotes a function with the following specification:
a.
function S'Machine (X : T)
return T
b. If X is a machine number of the type T, the function yields X;
otherwise, it yields the value obtained by rounding or truncating X
to either one of the adjacent machine numbers of the type T.
Constraint_Error is raised if rounding or truncating X to the
precision of the machine numbers results in a value outside the base
range of S. A zero result has the sign of X when S'Signed_Zeros is
True.
1. The following model-oriented attributes are defined for any subtype S of
a floating point type T.
2. S'Model_Mantissa
If the Numerics Annex is not supported, this attribute yields
an implementation defined value that is greater than or equal
to Ceiling(d*log (10)/log (T'Machine_Radix))+1, where d is
the requested decimal precision of T, and less than or equal
to the value of T'Machine_Mantissa. See G.2.2 for further
requirements that apply to implementations supporting the
Numerics Annex. The value of this attribute is of the type
universal_integer.
3. S'Model_Emin
If the Numerics Annex is not supported, this attribute yields
an implementation defined value that is greater than or equal
to the value of T'Machine_Emin. See G.2.2 for further
requirements that apply to implementations supporting the
Numerics Annex. The value of this attribute is of the type
universal_integer.
4. S'Model_Epsilon
Yields the value T'Machine_Radix ** 1-T'Model_Mantissa. The value
of this attribute is of the type universal_real.
5. S'Model_Small
Yields the value T'Machine_Radix ** T'Model_Emin-1. The value of
this attribute is of the type universal_real.
6. S'Model
S'Model denotes a function with the following specification:
a.
function S'Model (X : T)
return T
b. If the Numerics Annex is not supported, the meaning of this
attribute is implementation defined; See G.2.2 for the definition
that applies to implementations supporting the Numerics Annex.
1. S'Safe_First
Yields the lower bound of the safe range, see 3.5.7, of the
type T. If the Numerics Annex is not supported, the value of
this attribute is implementation defined; See G.2.2 for the
definition that applies to implementations supporting the
Numerics Annex. The value of this attribute is of the type
universal_real.
2. S'Safe_Last
Yields the upper bound of the safe range, see 3.5.7, of the
type T. If the Numerics Annex is not supported, the value of
this attribute is implementation defined; See G.2.2 for the
definition that applies to implementations supporting the
Numerics Annex. The value of this attribute is of the type
universal_real.
ΓòÉΓòÉΓòÉ 17.5.4. Attributes of Fixed Point Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The following representation-oriented attributes are defined for every
subtype S of a fixed point type T.
2. S'Machine_Radix
Yields the radix of the hardware representation of the type
T. The value of this attribute is of the type
universal_integer.
3. S'Machine_Rounds
Yields the value True if rounding is performed on inexact
results of every predefined operation that yields a result of
the type T; yields the value False otherwise. The value of
this attribute is of the predefined type Boolean.
4. S'Machine_Overflows
Yields the value True if overflow and divide-by-zero are
detected and reported by raising Constraint_Error for every
predefined operation that yields a result of the type T;
yields the value False otherwise. The value of this
attribute is of the predefined type Boolean.
ΓòÉΓòÉΓòÉ 17.6. Input-Output ΓòÉΓòÉΓòÉ
1. Input-output is provided through language-defined packages, each of which
is a child of the root package Ada. The generic packages Sequential_IO
and Direct_IO define input-output operations applicable to files
containing elements of a given type. The generic package Storage_IO
supports reading from and writing to an in-memory buffer. Additional
operations for text input-output are supplied in the packages Text_IO and
Wide_Text_IO. Heterogeneous input-output is provided through the child
packages Streams.Stream_IO and Text_IO.Text_Streams, see also 13.13. The
package IO_Exceptions defines the exceptions needed by the predefined
input-output packages.
ΓòÉΓòÉΓòÉ 17.7. External Files and File Objects ΓòÉΓòÉΓòÉ
Static Semantics
1. Values input from the external environment of the program, or output to
the external environment, are considered to occupy external files. An
external file can be anything external to the program that can produce a
value to be read or receive a value to be written. An external file is
identified by a string (the name). A second string (the form) gives
further system-dependent characteristics that may be associated with the
file, such as the physical organization or access rights. The conventions
governing the interpretation of such strings shall be documented.
2. Input and output operations are expressed as operations on objects of
some file type, rather than directly in terms of the external files. In
the remainder of this section, the term file is always used to refer to a
file object; the term external file is used otherwise.
3. Input-output for sequential files of values of a single element type is
defined by means of the generic package Sequential_IO. In order to define
sequential input-output for a given element type, an instantiation of
this generic unit, with the given type as actual parameter, has to be
declared. The resulting package contains the declaration of a file type
(called File_Type) for files of such elements, as well as the operations
applicable to these files, such as the Open, Read, and Write procedures.
4. Input-output for direct access files is likewise defined by a generic
package called Direct_IO. Input-output in human-readable form is defined
by the (nongeneric) packages Text_IO for Character and String data, and
Wide_Text_IO for Wide_Character and Wide_String data. Input-output for
files containing streams of elements representing values of possibly
different types is defined by means of the (nongeneric) package
Streams.Stream_IO.
5. Before input or output operations can be performed on a file, the file
first has to be associated with an external file. While such an
association is in effect, the file is said to be open, and otherwise the
file is said to be closed.
6. The language does not define what happens to external files after the
completion of the main program and all the library tasks (in particular,
if corresponding files have not been closed). The effect of input-output
for access types is unspecified.
7. An open file has a current mode, which is a value of one of the following
enumeration types:
8.
type File_Mode is (In_File, Inout_File, Out_File); -- for Direct_IO
a. These values correspond respectively to the cases where only
reading, both reading and writing, or only writing are to be
performed.
1.
type File_Mode is (In_File, Out_File, Append_File);
-- for Sequential_IO, Text_IO, Wide_Text_IO, and Stream_IO
a. These values correspond respectively to the cases where only
reading, only writing, or only appending are to be performed.
b. The mode of a file can be changed.
1. Several file management operations are common to Sequential_IO,
Direct_IO, Text_IO, and Wide_Text_IO. These operations are described in
subclause A.8.2, for sequential and direct files. Any additional effects
concerning text input-output are described in A.10.2.
2. The exceptions that can be propagated by the execution of an input-output
subprogram are defined in the package IO_Exceptions; the situations in
which they can be propagated are described following the description of
the subprogram (and in A.13). The exceptions Storage_Error and
Program_Error may be propagated. (Program_Error can only be propagated
due to errors made by the caller of the subprogram.) Finally, exceptions
can be propagated in certain implementation-defined situations.
NOTES
3. (18) Each instantiation of the generic packages Sequential_IO and
Direct_IO declares a different type File_Type. In the case of Text_IO,
Wide_Text_IO, and Streams.Stream_IO, the corresponding type File_Type is
unique.
4. (19) A bidirectional device can often be modeled as two sequential files
associated with the device, one of mode In_File, and one of mode
Out_File. An implementation may restrict the number of files that may be
associated with a given external file.
ΓòÉΓòÉΓòÉ 17.8. Sequential and Direct Files ΓòÉΓòÉΓòÉ
Static Semantics
1. Two kinds of access to external files are defined in this subclause:
sequential access and direct access. The corresponding file types and the
associated operations are provided by the generic packages Sequential_IO
and Direct_IO. A file object to be used for sequential access is called a
sequential file, and one to be used for direct access is called a direct
file. Access to stream files is described in A.12.1.
2. For sequential access, the file is viewed as a sequence of values that
are transferred in the order of their appearance (as produced by the
program or by the external environment). When the file is opened with
mode In_File or Out_File, transfer starts respectively from or to the
beginning of the file. When the file is opened with mode Append_File,
transfer to the file starts after the last element of the file.
3. For direct access, the file is viewed as a set of elements occupying
consecutive positions in linear order; a value can be transferred to or
from an element of the file at any selected position. The position of an
element is specified by its index, which is a number, greater than zero,
of the implementation-defined integer type Count. The first element, if
any, has index one; the index of the last element, if any, is called the
current size; the current size is zero if there are no elements. The
current size is a property of the external file.
4. An open direct file has a current index, which is the index that will be
used by the next read or write operation. When a direct file is opened,
the current index is set to one. The current index of a direct file is a
property of a file object, not of an external file.
A.8.1 The Generic Package Sequential_IO
A.8.2 File Management
A.8.3 Sequential Input-Output Operations
A.8.4 The Generic Package Direct_IO
A.8.5 Direct Input-Output Operations
ΓòÉΓòÉΓòÉ 17.8.1. The Generic Package Sequential_IO ΓòÉΓòÉΓòÉ
Static Semantics
1. The generic library package Sequential_IO has the following declaration:
2.
with Ada.IO_Exceptions;
generic
type Element_Type(<>) is private;
package Ada.Sequential_IO is
3.
type File_Type is limited private;
4.
type File_Mode is (In_File, Out_File, Append_File);
5.
-- File management
6.
procedure Create(File : in out File_Type;
Mode : in File_Mode := Out_File;
Name : in String := "";
Form : in String := "");
7.
procedure Open (File : in out File_Type;
Mode : in File_Mode;
Name : in String;
Form : in String := "");
8.
procedure Close (File : in out File_Type);
procedure Delete(File : in out File_Type);
procedure Reset (File : in out File_Type; Mode : in File_Mode);
procedure Reset (File : in out File_Type);
9.
function Mode (File : in File_Type) return File_Mode;
function Name (File : in File_Type) return String;
function Form (File : in File_Type) return String;
10.
function Is_Open(File : in File_Type) return Boolean;
11.
-- Input and output operations
12.
procedure Read (File : in File_Type; Item : out Element_Type);
procedure Write (File : in File_Type; Item : in Element_Type);
13.
function End_Of_File(File : in File_Type) return Boolean;
14.
-- Exceptions
15.
Status_Error : exception renames IO_Exceptions.Status_Error;
Mode_Error : exception renames IO_Exceptions.Mode_Error;
Name_Error : exception renames IO_Exceptions.Name_Error;
Use_Error : exception renames IO_Exceptions.Use_Error;
Device_Error : exception renames IO_Exceptions.Device_Error;
End_Error : exception renames IO_Exceptions.End_Error;
Data_Error : exception renames IO_Exceptions.Data_Error;
16.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Sequential_IO;
ΓòÉΓòÉΓòÉ 17.8.2. File Management ΓòÉΓòÉΓòÉ
Static Semantics
1. The procedures and functions described in this subclause provide for the
control of external files; their declarations are repeated in each of the
packages for sequential, direct, text, and stream input-output. For text
input-output, the procedures Create, Open, and Reset have additional
effects described in subclause (see A.10.2).
2.
procedure Create(File : in out File_Type;
Mode : in File_Mode := default_mode;
Name : in String := "";
Form : in String := "");
a. Establishes a new external file, with the given name and form, and
associates this external file with the given file. The given file is
left open. The current mode of the given file is set to the given
access mode. The default access mode is the mode Out_File for
sequential and text input-output; it is the mode Inout_File for
direct input-output. or direct access, the size of the created file
is implementation defined.
b. A null string for Name specifies an external file that is not
accessible after the completion of the main program (a temporary
file). A null string for Form specifies the use of the default
options of the implementation for the external file.
c. The exception Status_Error is propagated if the given file is
already open. The exception Name_Error is propagated if the string
given as Name does not allow the identification of an external file.
The exception Use_Error is propagated if, for the specified mode,
the external environment does not support creation of an external
file with the given name (in the absence of Name_Error) and form.
1.
procedure Open(File : in out File_Type;
Mode : in File_Mode;
Name : in String;
Form : in String := "");
a. Associates the given file with an existing external file having the
given name and form, and sets the current mode of the given file to
the given mode. The given file is left open.
b. The exception Status_Error is propagated if the given file is
already open. The exception Name_Error is propagated if the string
given as Name does not allow the identification of an external file;
in particular, this exception is propagated if no external file with
the given name exists. The exception Use_Error is propagated if, for
the specified mode, the external environment does not support
opening for an external file with the given name (in the absence of
Name_Error) and form.
1.
procedure Close(File : in out File_Type);
a. Severs the association between the given file and its associated
external file. The given file is left closed. In addition, for
sequential files, if the file being closed has mode Out_File or
Append_File, then the last element written since the most recent
open or reset is the last element that can be read from the file. If
no elements have been written and the file mode is Out_File, then
the closed file is empty. If no elements have been written and the
file mode is Append_File, then the closed file is unchanged.
b. The exception Status_Error is propagated if the given file is not
open.
1.
procedure Delete(File : in out File_Type);
a. Deletes the external file associated with the given file. The given
file is closed, and the external file ceases to exist.
b. The exception Status_Error is propagated if the given file is not
open. The exception Use_Error is propagated if deletion of the
external file is not supported by the external environment.
1.
procedure Reset(File : in out File_Type; Mode : in File_Mode);
procedure Reset(File : in out File_Type);
a. Resets the given file so that reading from its elements can be
restarted from the beginning of the file (for modes In_File and
Inout_File), and so that writing to its elements can be restarted at
the beginning of the file (for modes Out_File and Inout_File) or
after the last element of the file (for mode Append_File). In
particular, for direct access this means that the current index is
set to one. If a Mode parameter is supplied, the current mode of the
given file is set to the given mode. In addition, for sequential
files, if the given file has mode Out_File or Append_File when Reset
is called, the last element written since the most recent open or
reset is the last element that can be read from the file. If no
elements have been written and the file mode is Out_File, the reset
file is empty. If no elements have been written and the file mode is
Append_File, then the reset file is unchanged.
b. The exception Status_Error is propagated if the file is not open.
The exception Use_Error is propagated if the external environment
does not support resetting for the external file and, also, if the
external environment does not support resetting to the specified
mode for the external file.
1.
function Mode(File : in File_Type) return File_Mode;
a. Returns the current mode of the given file.
b. The exception Status_Error is propagated if the file is not open.
1.
function Name(File : in File_Type) return String;
a. Returns a string which uniquely identifies the external file
currently associated with the given file (and may thus be used in an
Open operation). If an external environment allows alternative
specifications of the name (for example, abbreviations), the string
returned by the function should correspond to a full specification
of the name.
b. The exception Status_Error is propagated if the given file is not
open. The exception Use_Error is propagated if the associated
external file is a temporary file that cannot be opened by any name.
1.
function Form(File : in File_Type) return String;
a. Returns the form string for the external file currently associated
with the given file. If an external environment allows alternative
specifications of the form (for example, abbreviations using default
options), the string returned by the function should correspond to a
full specification (that is, it should indicate explicitly all
options selected, including default options).
b. The exception Status_Error is propagated if the given file is not
open.
1.
function Is_Open(File : in File_Type) return Boolean;
a. Returns True if the file is open (that is, if it is associated with
an external file), otherwise returns False.
Implementation Permissions
1. An implementation may propagate Name_Error or Use_Error if an attempt is
made to use an I/O feature that cannot be supported by the implementation
due to limitations in the external environment. Any such restriction
should be documented.
ΓòÉΓòÉΓòÉ 17.8.3. Sequential Input-Output Operations ΓòÉΓòÉΓòÉ
Static Semantics
1. The operations available for sequential input and output are described in
this subclause. The exception Status_Error is propagated if any of these
operations is attempted for a file that is not open.
2.
procedure Read(File : in File_Type; Item : out Element_Type);
a. Operates on a file of mode In_File. Reads an element from the given
file, and returns the value of this element in the Item parameter.
b. The exception Mode_Error is propagated if the mode is not In_File.
The exception End_Error is propagated if no more elements can be
read from the given file. The exception Data_Error can be propagated
if the element read cannot be interpreted as a value of the subtype
Element_Type, see A.13: ``Exceptions in Input-Output''.
1.
procedure Write(File : in File_Type; Item : in Element_Type);
a. Operates on a file of mode Out_File or Append_File. Writes the value
of Item to the given file.
b. The exception Mode_Error is propagated if the mode is not Out_File
or Append_File. The exception Use_Error is propagated if the
capacity of the external file is exceeded.
1.
function End_Of_File(File : in File_Type) return Boolean;
a. Operates on a file of mode In_File. Returns True if no more elements
can be read from the given file; otherwise returns False.
b. The exception Mode_Error is propagated if the mode is not In_File.
ΓòÉΓòÉΓòÉ 17.8.4. The Generic Package Direct_IO ΓòÉΓòÉΓòÉ
Static Semantics
1. The generic library package Direct_IO has the following declaration:
2.
with Ada.IO_Exceptions;
generic
type Element_Type is private;
package Ada.Direct_IO is
3.
type File_Type is limited private;
4.
type File_Mode is (In_File, Inout_File, Out_File);
type Count is range 0 ┬╖┬╖ implementation-defined;
subtype Positive_Count is Count range 1 ┬╖┬╖ Count'Last;
5.
-- File management
6.
procedure Create(File : in out File_Type;
Mode : in File_Mode := Inout_File;
Name : in String := "";
Form : in String := "");
7.
procedure Open (File : in out File_Type;
Mode : in File_Mode;
Name : in String;
Form : in String := "");
8.
procedure Close (File : in out File_Type);
procedure Delete(File : in out File_Type);
procedure Reset (File : in out File_Type; Mode : in File_Mode);
procedure Reset (File : in out File_Type);
9.
function Mode (File : in File_Type) return File_Mode;
function Name (File : in File_Type) return String;
function Form (File : in File_Type) return String;
10.
function Is_Open(File : in File_Type) return Boolean;
11.
-- Input and output operations
12.
procedure Read (File : in File_Type; Item : out Element_Type;
From : in Positive_Count);
procedure Read (File : in File_Type; Item : out Element_Type);
13.
procedure Write(File : in File_Type; Item : in Element_Type;
To : in Positive_Count);
procedure Write(File : in File_Type; Item : in Element_Type);
14.
procedure Set_Index(File : in File_Type; To : in Positive_Count);
15.
function Index(File : in File_Type) return Positive_Count;
function Size (File : in File_Type) return Count;
16.
function End_Of_File(File : in File_Type) return Boolean;
17.
-- Exceptions
18.
Status_Error : exception renames IO_Exceptions.Status_Error;
Mode_Error : exception renames IO_Exceptions.Mode_Error;
Name_Error : exception renames IO_Exceptions.Name_Error;
Use_Error : exception renames IO_Exceptions.Use_Error;
Device_Error : exception renames IO_Exceptions.Device_Error;
End_Error : exception renames IO_Exceptions.End_Error;
Data_Error : exception renames IO_Exceptions.Data_Error;
19.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Direct_IO;
ΓòÉΓòÉΓòÉ 17.8.5. Direct Input-Output Operations ΓòÉΓòÉΓòÉ
Static Semantics
1. The operations available for direct input and output are described in
this subclause. The exception Status_Error is propagated if any of these
operations is attempted for a file that is not open.
2.
procedure Read(File : in File_Type; Item : out Element_Type;
From : in Positive_Count);
procedure Read(File : in File_Type; Item : out Element_Type);
a. Operates on a file of mode In_File or Inout_File. In the case of the
first form, sets the current index of the given file to the index
value given by the parameter From. Then (for both forms) returns, in
the parameter Item, the value of the element whose position in the
given file is specified by the current index of the file; finally,
increases the current index by one.
b. The exception Mode_Error is propagated if the mode of the given file
is Out_File. The exception End_Error is propagated if the index to
be used exceeds the size of the external file. The exception
Data_Error can be propagated if the element read cannot be
interpreted as a value of the subtype Element_Type, see A.13.
1.
procedure Write(File : in File_Type; Item : in Element_Type;
To : in Positive_Count);
procedure Write(File : in File_Type; Item : in Element_Type);
a. Operates on a file of mode Inout_File or Out_File. In the case of
the first form, sets the index of the given file to the index value
given by the parameter To. Then (for both forms) gives the value of
the parameter Item to the element whose position in the given file
is specified by the current index of the file; finally, increases
the current index by one.
b. The exception Mode_Error is propagated if the mode of the given file
is In_File. The exception Use_Error is propagated if the capacity of
the external file is exceeded.
1.
procedure Set_Index(File : in File_Type; To : in Positive_Count);
a. Operates on a file of any mode. Sets the current index of the given
file to the given index value (which may exceed the current size of
the file).
1.
function Index(File : in File_Type) return Positive_Count;
a. Operates on a file of any mode. Returns the current index of the
given file.
1.
function Size(File : in File_Type) return Count;
a. Operates on a file of any mode. Returns the current size of the
external file that is associated with the given file.
1.
function End_Of_File(File : in File_Type) return Boolean;
a. Operates on a file of mode In_File or Inout_File. Returns True if
the current index exceeds the size of the external file; otherwise
returns False.
b. The exception Mode_Error is propagated if the mode of the given file
is Out_File.
NOTES
1. (20) Append_File mode is not supported for the generic package Direct_IO.
ΓòÉΓòÉΓòÉ 17.9. The Generic Package Storage_IO ΓòÉΓòÉΓòÉ
1. The generic package Storage_IO provides for reading from and writing to
an in-memory buffer. This generic package supports the construction of
user-defined input-output packages.
Static Semantics
2. The generic library package Storage_IO has the following declaration:
3.
with Ada.IO_Exceptions;
with System.Storage_Elements;
generic
type Element_Type is private;
package Ada.Storage_IO is
pragma Preelaborate(Storage_IO);
4.
Buffer_Size : constant System.Storage_Elements.Storage_Count
:= implementation-defined;
subtype Buffer_Type is
System.Storage_Elements.Storage_Array (1┬╖┬╖Buffer_Size);
5.
-- Input and output operations
6.
procedure Read (Buffer : in Buffer_Type;
Item : out Element_Type);
7.
procedure Write(Buffer : out Buffer_Type;
Item : in Element_Type);
8.
-- Exceptions
9.
Data_Error : exception renames IO_Exceptions.Data_Error;
end Ada.Storage_IO;
10. In each instance, the constant Buffer_Size has a value that is the size
(in storage elements) of the buffer required to represent the content of
an object of subtype Element_Type, including any implicit levels of
indirection used by the implementation. The Read and Write procedures of
Storage_IO correspond to the Read and Write procedures of Direct_IO (see
A.8.4) but with the content of the Item parameter being read from or
written into the specified Buffer, rather than an external file.
NOTES
11. (21) A buffer used for Storage_IO holds only one element at a time; an
external file used for Direct_IO holds a sequence of elements.
ΓòÉΓòÉΓòÉ 17.10. Text Input-Output ΓòÉΓòÉΓòÉ
Static Semantics
1. This clause describes the package Text_IO, which provides facilities for
input and output in human-readable form. Each file is read or written
sequentially, as a sequence of characters grouped into lines, and as a
sequence of lines grouped into pages. The specification of the package is
given below in subclause (see A.10.1).
2. The facilities for file management given above, in A.8.2 and A.8.3, are
available for text input-output. In place of Read and Write, however,
there are procedures Get and Put that input values of suitable types from
text files, and output values to them. These values are provided to the
Put procedures, and returned by the Get procedures, in a parameter Item.
Several overloaded procedures of these names exist, for different types
of Item. These Get procedures analyze the input sequences of characters
based on lexical elements (see 2.) and return the corresponding values;
the Put procedures output the given values as appropriate lexical
elements. Procedures Get and Put are also available that input and output
individual characters treated as character values rather than as lexical
elements. Related to character input are procedures to look ahead at the
next character without reading it, and to read a character
``immediately'' without waiting for an end-of-line to signal
availability.
3. In addition to the procedures Get and Put for numeric and enumeration
types of Item that operate on text files, analogous procedures are
provided that read from and write to a parameter of type String. These
procedures perform the same analysis and composition of character
sequences as their counterparts which have a file parameter.
4. For all Get and Put procedures that operate on text files, and for many
other subprograms, there are forms with and without a file parameter.
Each such Get procedure operates on an input file, and each such Put
procedure operates on an output file. If no file is specified, a default
input file or a default output file is used.
5. At the beginning of program execution the default input and output files
are the so-called standard input file and standard output file. These
files are open, have respectively the current modes In_File and Out_File,
and are associated with two implementation-defined external files.
Procedures are provided to change the current default input file and the
current default output file.
6. At the beginning of program execution a default file for
program-dependent error-related text output is the so-called standard
error file. This file is open, has the current mode Out_File, and is
associated with an implementation-defined external file. A procedure is
provided to change the current default error file.
7. From a logical point of view, a text file is a sequence of pages, a page
is a sequence of lines, and a line is a sequence of characters; the end
of a line is marked by a line terminator; the end of a page is marked by
the combination of a line terminator immediately followed by a page
terminator; and the end of a file is marked by the combination of a line
terminator immediately followed by a page terminator and then a file
terminator. Terminators are generated during output; either by calls of
procedures provided expressly for that purpose; or implicitly as part of
other operations, for example, when a bounded line length, a bounded page
length, or both, have been specified for a file.
8. The actual nature of terminators is not defined by the language and hence
depends on the implementation. Although terminators are recognized or
generated by certain of the procedures that follow, they are not
necessarily implemented as characters or as sequences of characters.
Whether they are characters (and if so which ones) in any particular
implementation need not concern a user who neither explicitly outputs nor
explicitly inputs control characters. The effect of input (Get) or output
(Put) of control characters (other than horizontal tabulation) is not
specified by the language.
9. The characters of a line are numbered, starting from one; the number of a
character is called its column number. For a line terminator, a column
number is also defined: it is one more than the number of characters in
the line. The lines of a page, and the pages of a file, are similarly
numbered. The current column number is the column number of the next
character or line terminator to be transferred. The current line number
is the number of the current line. The current page number is the number
of the current page. These numbers are values of the subtype
Positive_Count of the type Count (by convention, the value zero of the
type Count is used to indicate special conditions).
10.
type Count is range 0 ┬╖┬╖ implementation-defined;
subtype Positive_Count is Count range 1 ┬╖┬╖ Count'Last;
11. For an output file or an append file, a maximum line length can be
specified and a maximum page length can be specified. If a value to be
output cannot fit on the current line, for a specified maximum line
length, then a new line is automatically started before the value is
output; if, further, this new line cannot fit on the current page, for a
specified maximum page length, then a new page is automatically started
before the value is output. Functions are provided to determine the
maximum line length and the maximum page length. When a file is opened
with mode Out_File or Append_File, both values are zero: by convention,
this means that the line lengths and page lengths are unbounded.
(Consequently, output consists of a single line if the subprograms for
explicit control of line and page structure are not used.) The constant
Unbounded is provided for this purpose.
A.10.1 The Package Text_IO
A.10.2 Text File Management
A.10.3 Default Input, Output, and Error Files
A.10.4 Specification of Line and Page Lengths
A.10.5 Operations on Columns, Lines, and Pages
A.10.6 Get and Put Procedures
A.10.7 Input-Output of Characters and Strings
A.10.8 Input-Output for Integer Types
A.10.9 Input-Output for Real Types
A.10.10 Input-Output for Enumeration Types
ΓòÉΓòÉΓòÉ 17.10.1. The Package Text_IO ΓòÉΓòÉΓòÉ
Static Semantics
1. The library package Text_IO has the following declaration:
2.
with Ada.IO_Exceptions;
package Ada.Text_IO is
3.
type File_Type is limited private;
4.
type File_Mode is (In_File, Out_File, Append_File);
5.
type Count is range 0 ┬╖┬╖ implementation-defined;
subtype Positive_Count is Count range 1 ┬╖┬╖ Count'Last;
Unbounded : constant Count := 0; -- line and page length
6.
subtype Field is Integer range 0 ┬╖┬╖ implementation-defined;
subtype Number_Base is Integer range 2 ┬╖┬╖ 16;
7.
type Type_Set is (Lower_Case, Upper_Case);
8.
-- File Management
9.
procedure Create (File : in out File_Type;
Mode : in File_Mode := Out_File;
Name : in String := "";
Form : in String := "");
10.
procedure Open (File : in out File_Type;
Mode : in File_Mode;
Name : in String;
Form : in String := "");
11.
procedure Close (File : in out File_Type);
procedure Delete (File : in out File_Type);
procedure Reset (File : in out File_Type; Mode : in File_Mode);
procedure Reset (File : in out File_Type);
12.
function Mode (File : in File_Type) return File_Mode;
function Name (File : in File_Type) return String;
function Form (File : in File_Type) return String;
13.
function Is_Open(File : in File_Type) return Boolean;
14.
-- Control of default input and output files
15.
procedure Set_Input (File : in File_Type);
procedure Set_Output(File : in File_Type);
procedure Set_Error (File : in File_Type);
16.
function Standard_Input return File_Type;
function Standard_Output return File_Type;
function Standard_Error return File_Type;
17.
function Current_Input return File_Type;
function Current_Output return File_Type;
function Current_Error return File_Type;
18.
type File_Access is access constant File_Type;
19.
function Standard_Input return File_Access;
function Standard_Output return File_Access;
function Standard_Error return File_Access;
20.
function Current_Input return File_Access;
function Current_Output return File_Access;
function Current_Error return File_Access;
21.
--Buffer control
procedure Flush (File : in out File_Type);
procedure Flush;
22.
-- Specification of line and page lengths
23.
procedure Set_Line_Length(File : in File_Type; To : in Count);
procedure Set_Line_Length(To : in Count);
24.
procedure Set_Page_Length(File : in File_Type; To : in Count);
procedure Set_Page_Length(To : in Count);
25.
function Line_Length(File : in File_Type) return Count;
function Line_Length return Count;
26.
function Page_Length(File : in File_Type) return Count;
function Page_Length return Count;
27.
-- Column, Line, and Page Control
28.
procedure New_Line (File : in File_Type;
Spacing : in Positive_Count := 1);
procedure New_Line (Spacing : in Positive_Count := 1);
29.
procedure Skip_Line (File : in File_Type;
Spacing : in Positive_Count := 1);
procedure Skip_Line (Spacing : in Positive_Count := 1);
30.
function End_Of_Line(File : in File_Type) return Boolean;
function End_Of_Line return Boolean;
31.
procedure New_Page (File : in File_Type);
procedure New_Page;
32.
procedure Skip_Page (File : in File_Type);
procedure Skip_Page;
33.
function End_Of_Page(File : in File_Type) return Boolean;
function End_Of_Page return Boolean;
34.
function End_Of_File(File : in File_Type) return Boolean;
function End_Of_File return Boolean;
35.
procedure Set_Col (File : in File_Type; To : in Positive_Count);
procedure Set_Col (To : in Positive_Count);
36.
procedure Set_Line(File : in File_Type; To : in Positive_Count);
procedure Set_Line(To : in Positive_Count);
37.
function Col (File : in File_Type) return Positive_Count;
function Col return Positive_Count;
38.
function Line(File : in File_Type) return Positive_Count;
function Line return Positive_Count;
39.
function Page(File : in File_Type) return Positive_Count;
function Page return Positive_Count;
40.
-- Character Input-Output
41.
procedure Get(File : in File_Type; Item : out Character);
procedure Get(Item : out Character);
42.
procedure Put(File : in File_Type; Item : in Character);
procedure Put(Item : in Character);
43.
procedure Look_Ahead (File : in File_Type;
Item : out Character;
End_Of_Line : out Boolean);
procedure Look_Ahead (Item : out Character;
End_Of_Line : out Boolean);
44.
procedure Get_Immediate(File : in File_Type;
Item : out Character);
procedure Get_Immediate(Item : out Character);
45.
procedure Get_Immediate(File : in File_Type;
Item : out Character;
Available : out Boolean);
procedure Get_Immediate(Item : out Character;
Available : out Boolean);
46.
-- String Input-Output
47.
procedure Get(File : in File_Type; Item : out String);
procedure Get(Item : out String);
48.
procedure Put(File : in File_Type; Item : in String);
procedure Put(Item : in String);
49.
procedure Get_Line(File : in File_Type;
Item : out String;
Last : out Natural);
procedure Get_Line(Item : out String; Last : out Natural);
50.
procedure Put_Line(File : in File_Type; Item : in String);
procedure Put_Line(Item : in String);
51.
-- Generic packages for Input-Output of Integer Types
52.
generic
type Num is range <>;
package Integer_IO is
53.
Default_Width : Field := Num'Width;
Default_Base : Number_Base := 10;
54.
procedure Get(File : in File_Type;
Item : out Num;
Width : in Field := 0);
procedure Get(Item : out Num;
Width : in Field := 0);
55.
procedure Put(File : in File_Type;
Item : in Num;
Width : in Field := Default_Width;
Base : in Number_Base := Default_Base);
procedure Put(Item : in Num;
Width : in Field := Default_Width;
Base : in Number_Base := Default_Base);
procedure Get(From : in String;
Item : out Num;
Last : out Positive);
procedure Put(To : out String;
Item : in Num;
Base : in Number_Base := Default_Base);
56.
end Integer_IO;
57.
generic
type Num is mod <>;
package Modular_IO is
58.
Default_Width : Field := Num'Width;
Default_Base : Number_Base := 10;
59.
procedure Get(File : in File_Type;
Item : out Num;
Width : in Field := 0);
procedure Get(Item : out Num;
Width : in Field := 0);
60.
procedure Put(File : in File_Type;
Item : in Num;
Width : in Field := Default_Width;
Base : in Number_Base := Default_Base);
procedure Put(Item : in Num;
Width : in Field := Default_Width;
Base : in Number_Base := Default_Base);
procedure Get(From : in String;
Item : out Num;
Last : out Positive);
procedure Put(To : out String;
Item : in Num;
Base : in Number_Base := Default_Base);
61.
end Modular_IO;
62.
-- Generic packages for Input-Output of Real Types
63.
generic
type Num is digits <>;
package Float_IO is
64.
Default_Fore : Field := 2;
Default_Aft : Field := Num'Digits-1;
Default_Exp : Field := 3;
65.
procedure Get(File : in File_Type;
Item : out Num;
Width : in Field := 0);
procedure Get(Item : out Num;
Width : in Field := 0);
66.
procedure Put(File : in File_Type;
Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
procedure Put(Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
67.
procedure Get(From : in String;
Item : out Num;
Last : out Positive);
procedure Put(To : out String;
Item : in Num;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
end Float_IO;
68.
generic
type Num is delta <>;
package Fixed_IO is
69.
Default_Fore : Field := Num'Fore;
Default_Aft : Field := Num'Aft;
Default_Exp : Field := 0;
70.
procedure Get(File : in File_Type;
Item : out Num;
Width : in Field := 0);
procedure Get(Item : out Num;
Width : in Field := 0);
71.
procedure Put(File : in File_Type;
Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
procedure Put(Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
72.
procedure Get(From : in String;
Item : out Num;
Last : out Positive);
procedure Put(To : out String;
Item : in Num;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
end Fixed_IO;
73.
generic
type Num is delta <> digits <>;
package Decimal_IO is
74.
Default_Fore : Field := Num'Fore;
Default_Aft : Field := Num'Aft;
Default_Exp : Field := 0;
75.
procedure Get(File : in File_Type;
Item : out Num;
Width : in Field := 0);
procedure Get(Item : out Num;
Width : in Field := 0);
76.
procedure Put(File : in File_Type;
Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
procedure Put(Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
77.
procedure Get(From : in String;
Item : out Num;
Last : out Positive);
procedure Put(To : out String;
Item : in Num;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
end Decimal_IO;
78.
-- Generic package for Input-Output of Enumeration Types
79.
generic
type Enum is (<>);
package Enumeration_IO is
80.
Default_Width : Field := 0;
Default_Setting : Type_Set := Upper_Case;
81.
procedure Get(File : in File_Type;
Item : out Enum);
procedure Get(Item : out Enum);
82.
procedure Put(File : in File_Type;
Item : in Enum;
Width : in Field := Default_Width;
Set : in Type_Set := Default_Setting);
procedure Put(Item : in Enum;
Width : in Field := Default_Width;
Set : in Type_Set := Default_Setting);
83.
procedure Get(From : in String;
Item : out Enum;
Last : out Positive);
procedure Put(To : out String;
Item : in Enum;
Set : in Type_Set := Default_Setting);
end Enumeration_IO;
84.
-- Exceptions
85.
Status_Error : exception renames IO_Exceptions.Status_Error;
Mode_Error : exception renames IO_Exceptions.Mode_Error;
Name_Error : exception renames IO_Exceptions.Name_Error;
Use_Error : exception renames IO_Exceptions.Use_Error;
Device_Error : exception renames IO_Exceptions.Device_Error;
End_Error : exception renames IO_Exceptions.End_Error;
Data_Error : exception renames IO_Exceptions.Data_Error;
Layout_Error : exception renames IO_Exceptions.Layout_Error;
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Text_IO;
ΓòÉΓòÉΓòÉ 17.10.2. Text File Management ΓòÉΓòÉΓòÉ
Static Semantics
1. The only allowed file modes for text files are the modes In_File,
Out_File, and Append_File. The subprograms given in A.8.2, for the
control of external files, and the function End_Of_File given in A.8.3,
for sequential input-output, are also available for text files. There is
also a version of End_Of_File that refers to the current default input
file. For text files, the procedures have the following additional
effects:
a. For the procedures Create and Open: After a file with mode Out_File
or Append_File is opened, the page length and line length are
unbounded (both have the conventional value zero). After a file (of
any mode) is opened, the current column, current line, and current
page numbers are set to one. If the mode is Append_File, it is
implementation defined whether a page terminator will separate
preexisting text in the file from the new text to be written.
b. For the procedure Close: If the file has the current mode Out_File
or Append_File, has the effect of calling New_Page, unless the
current page is already terminated; then outputs a file terminator.
c. For the procedure Reset: If the file has the current mode Out_File
or Append_File, has the effect of calling New_Page, unless the
current page is already terminated; then outputs a file terminator.
The current column, line, and page numbers are set to one, and the
line and page lengths to Unbounded. If the new mode is Append_File,
it is implementation defined whether a page terminator will separate
preexisting text in the file from the new text to be written.
1. The exception Mode_Error is propagated by the procedure Reset upon an
attempt to change the mode of a file that is the current default input
file, the current default output file, or the current default error file.
NOTES
2. (22) An implementation can define the Form parameter of Create and Open
to control effects including the following:
a. the interpretation of line and column numbers for an interactive
file, and
b. the interpretation of text formats in a file created by a foreign
program.
ΓòÉΓòÉΓòÉ 17.10.3. Default Input, Output, and Error Files ΓòÉΓòÉΓòÉ
Static Semantics
1. The following subprograms provide for the control of the particular
default files that are used when a file parameter is omitted from a Get,
Put, or other operation of text input-output described below, or when
application-dependent error-related text is to be output.
2.
procedure Set_Input(File : in File_Type);
a. Operates on a file of mode In_File. Sets the current default input
file to File.
b. The exception Status_Error is propagated if the given file is not
open. The exception Mode_Error is propagated if the mode of the
given file is not In_File.
1.
procedure Set_Output(File : in File_Type);
procedure Set_Error (File : in File_Type);
a. Each operates on a file of mode Out_File or Append_File. Set_Output
sets the current default output file to File. Set_Error sets the
current default error file to File. The exception Status_Error is
propagated if the given file is not open. The exception Mode_Error
is propagated if the mode of the given file is not Out_File or
Append_File.
1.
function Standard_Input return File_Type;
function Standard_Input return File_Access;
a. Returns the standard input file, see A.10, or an access value
designating the standard input file, respectively.
1.
function Standard_Output return File_Type;
function Standard_Output return File_Access;
a. Returns the standard output file, see A.10, or an access value
designating the standard output file, respectively.
1.
function Standard_Error return File_Type;
function Standard_Error return File_Access;
a. Returns the standard error file, see A.10, or an access value
designating the standard output file, respectively.
b. The Form strings implicitly associated with the opening of
Standard_Input, Standard_Output, and Standard_Error at the start of
program execution are implementation defined.
1.
function Current_Input return File_Type;
function Current_Input return File_Access;
a. Returns the current default input file, or an access value
designating the current default input file, respectively.
1.
function Current_Output return File_Type;
function Current_Output return File_Access;
a. Returns the current default output file, or an access value
designating the current default output file, respectively.
1.
function Current_Error return File_Type;
function Current_Error return File_Access;
a. Returns the current default error file, or an access value
designating the current default error file, respectively.
1.
procedure Flush (File : in out File_Type);
procedure Flush;
a. The effect of Flush is the same as the corresponding subprogram in
Streams.Stream_IO, see A.12.1. If File is not explicitly specified,
Current_Output is used.
Erroneous Execution
1. The execution of a program is erroneous if it attempts to use a current
default input, default output, or default error file that no longer
exists.
2. If the Close operation is applied to a file object that is also serving
as the default input, default output, or default error file, then
subsequent operations on such a default file are erroneous.
NOTES
3. (23) The standard input, standard output, and standard error files cannot
be opened, closed, reset, or deleted, because the parameter File of the
corresponding procedures has the mode in out.
4. (24) The standard input, standard output, and standard error files are
different file objects, but not necessarily different external files.
ΓòÉΓòÉΓòÉ 17.10.4. Specification of Line and Page Lengths ΓòÉΓòÉΓòÉ
Static Semantics
1. The subprograms described in this subclause are concerned with the line
and page structure of a file of mode Out_File or Append_File. They
operate either on the file given as the first parameter, or, in the
absence of such a file parameter, on the current default output file.
They provide for output of text with a specified maximum line length or
page length. In these cases, line and page terminators are output
implicitly and automatically when needed. When line and page lengths are
unbounded (that is, when they have the conventional value zero), as in
the case of a newly opened file, new lines and new pages are only started
when explicitly called for.
2. In all cases, the exception Status_Error is propagated if the file to be
used is not open; the exception Mode_Error is propagated if the mode of
the file is not Out_File or Append_File.
3.
procedure Set_Line_Length(File : in File_Type; To : in Count);
procedure Set_Line_Length(To : in Count);
a. Sets the maximum line length of the specified output or append file
to the number of characters specified by To. The value zero for To
specifies an unbounded line length.
b. The exception Use_Error is propagated if the specified line length
is inappropriate for the associated external file.
1.
procedure Set_Page_Length(File : in File_Type; To : in Count);
procedure Set_Page_Length(To : in Count);
a. Sets the maximum page length of the specified output or append file
to the number of lines specified by To. The value zero for To
specifies an unbounded page length.
b. The exception Use_Error is propagated if the specified page length
is inappropriate for the associated external file.
1.
function Line_Length(File : in File_Type) return Count;
function Line_Length return Count;
a. Returns the maximum line length currently set for the specified
output or append file, or zero if the line length is unbounded.
1.
function Page_Length(File : in File_Type) return Count;
function Page_Length return Count;
a. Returns the maximum page length currently set for the specified
output or append file, or zero if the page length is unbounded.
ΓòÉΓòÉΓòÉ 17.10.5. Operations on Columns, Lines, and Pages ΓòÉΓòÉΓòÉ
Static Semantics
1. The subprograms described in this subclause provide for explicit control
of line and page structure; they operate either on the file given as the
first parameter, or, in the absence of such a file parameter, on the
appropriate (input or output) current default file. The exception
Status_Error is propagated by any of these subprograms if the file to be
used is not open.
2.
procedure New_Line(File : in File_Type;
Spacing : in Positive_Count := 1);
procedure New_Line(Spacing : in Positive_Count := 1);
a. Operates on a file of mode Out_File or Append_File.
b. For a Spacing of one: Outputs a line terminator and sets the current
column number to one. Then increments the current line number by
one, except in the case that the current line number is already
greater than or equal to the maximum page length, for a bounded page
length; in that case a page terminator is output, the current page
number is incremented by one, and the current line number is set to
one.
c. For a Spacing greater than one, the above actions are performed
Spacing times.
d. The exception Mode_Error is propagated if the mode is not Out_File
or Append_File.
1.
procedure Skip_Line(File : in File_Type;
Spacing : in Positive_Count := 1);
procedure Skip_Line(Spacing : in Positive_Count := 1);
a. Operates on a file of mode In_File.
b. For a Spacing of one: Reads and discards all characters until a line
terminator has been read, and then sets the current column number to
one. If the line terminator is not immediately followed by a page
terminator, the current line number is incremented by one.
Otherwise, if the line terminator is immediately followed by a page
terminator, then the page terminator is skipped, the current page
number is incremented by one, and the current line number is set to
one.
c. For a Spacing greater than one, the above actions are performed
Spacing times.
d. The exception Mode_Error is propagated if the mode is not In_File.
The exception End_Error is propagated if an attempt is made to read
a file terminator.
1.
function End_Of_Line(File : in File_Type) return Boolean;
function End_Of_Line return Boolean;
a. Operates on a file of mode In_File. Returns True if a line
terminator or a file terminator is next; otherwise returns False.
b. The exception Mode_Error is propagated if the mode is not In_File.
1.
procedure New_Page(File : in File_Type);
procedure New_Page;
a. Operates on a file of mode Out_File or Append_File. Outputs a line
terminator if the current line is not terminated, or if the current
page is empty (that is, if the current column and line numbers are
both equal to one). Then outputs a page terminator, which terminates
the current page. Adds one to the current page number and sets the
current column and line numbers to one.
b. The exception Mode_Error is propagated if the mode is not Out_File
or Append_File.
1.
procedure Skip_Page(File : in File_Type);
procedure Skip_Page;
a. Operates on a file of mode In_File. Reads and discards all
characters and line terminators until a page terminator has been
read. Then adds one to the current page number, and sets the current
column and line numbers to one.
b. The exception Mode_Error is propagated if the mode is not In_File.
The exception End_Error is propagated if an attempt is made to read
a file terminator.
1.
function End_Of_Page(File : in File_Type) return Boolean;
function End_Of_Page return Boolean;
a. Operates on a file of mode In_File. Returns True if the combination
of a line terminator and a page terminator is next, or if a file
terminator is next; otherwise returns False.
b. The exception Mode_Error is propagated if the mode is not In_File.
1.
function End_Of_File(File : in File_Type) return Boolean;
function End_Of_File return Boolean;
a. Operates on a file of mode In_File. Returns True if a file
terminator is next, or if the combination of a line, a page, and a
file terminator is next; otherwise returns False.
b. The exception Mode_Error is propagated if the mode is not In_File.
c. The following subprograms provide for the control of the current
position of reading or writing in a file. In all cases, the default
file is the current output file.
1.
procedure Set_Col(File : in File_Type; To : in Positive_Count);
procedure Set_Col(To : in Positive_Count);
a. If the file mode is Out_File or Append_File:
1. If the value specified by To is greater than the current column
number, outputs spaces, adding one to the current column number
after each space, until the current column number equals the
specified value. If the value specified by To is equal to the
current column number, there is no effect. If the value
specified by To is less than the current column number, has the
effect of calling New_Line (with a spacing of one), then
outputs (To - 1) spaces, and sets the current column number to
the specified value.
2. The exception Layout_Error is propagated if the value specified
by To exceeds Line_Length when the line length is bounded (that
is, when it does not have the conventional value zero).
a. If the file mode is In_File:
1. Reads (and discards) individual characters, line terminators,
and page terminators, until the next character to be read has a
column number that equals the value specified by To; there is
no effect if the current column number already equals this
value. Each transfer of a character or terminator maintains the
current column, line, and page numbers in the same way as a Get
procedure, see A.10.6. (Short lines will be skipped until a
line is reached that has a character at the specified column
position.)
2. The exception End_Error is propagated if an attempt is made to
read a file terminator.
1.
procedure Set_Line(File : in File_Type; To : in Positive_Count);
procedure Set_Line(To : in Positive_Count);
a. If the file mode is Out_File or Append_File:
1. If the value specified by To is greater than the current line
number, has the effect of repeatedly calling New_Line (with a
spacing of one), until the current line number equals the
specified value. If the value specified by To is equal to the
current line number, there is no effect. If the value specified
by To is less than the current line number, has the effect of
calling New_Page followed by a call of New_Line with a spacing
equal to (To - 1).
2. The exception Layout_Error is propagated if the value specified
by To exceeds Page_Length when the page length is bounded (that
is, when it does not have the conventional value zero).
a. If the mode is In_File:
1. Has the effect of repeatedly calling Skip_Line (with a spacing
of one), until the current line number equals the value
specified by To; there is no effect if the current line number
already equals this value. (Short pages will be skipped until a
page is reached that has a line at the specified line
position.)
2. The exception End_Error is propagated if an attempt is made to
read a file terminator.
1.
function Col(File : in File_Type) return Positive_Count;
function Col return Positive_Count;
a. Returns the current column number.
b. The exception Layout_Error is propagated if this number exceeds
Count'Last.
1.
function Line(File : in File_Type) return Positive_Count;
function Line return Positive_Count;
a. Returns the current line number.
b. The exception Layout_Error is propagated if this number exceeds
Count'Last.
1.
function Page(File : in File_Type) return Positive_Count;
function Page return Positive_Count;
a. Returns the current page number.
b. The exception Layout_Error is propagated if this number exceeds
Count'Last.
1. The column number, line number, or page number are allowed to exceed
Count'Last (as a consequence of the input or output of sufficiently many
characters, lines, or pages). These events do not cause any exception to
be propagated. However, a call of Col, Line, or Page propagates the
exception Layout_Error if the corresponding number exceeds Count'Last.
NOTES
2. (25) A page terminator is always skipped whenever the preceding line
terminator is skipped. An implementation may represent the combination of
these terminators by a single character, provided that it is properly
recognized on input.
ΓòÉΓòÉΓòÉ 17.10.6. Get and Put Procedures ΓòÉΓòÉΓòÉ
Static Semantics
1. The procedures Get and Put for items of the type Character, String,
numeric types, and enumeration types are described in subsequent
subclauses. Features of these procedures that are common to most of these
types are described in this subclause. The Get and Put procedures for
items of type Character and String deal with individual character values;
the Get and Put procedures for numeric and enumeration types treat the
items as lexical elements.
2. All procedures Get and Put have forms with a file parameter, written
first. Where this parameter is omitted, the appropriate (input or output)
current default file is understood to be specified. Each procedure Get
operates on a file of mode In_File. Each procedure Put operates on a file
of mode Out_File or Append_File.
3. All procedures Get and Put maintain the current column, line, and page
numbers of the specified file: the effect of each of these procedures
upon these numbers is the result of the effects of individual transfers
of characters and of individual output or skipping of terminators. Each
transfer of a character adds one to the current column number. Each
output of a line terminator sets the current column number to one and
adds one to the current line number. Each output of a page terminator
sets the current column and line numbers to one and adds one to the
current page number. For input, each skipping of a line terminator sets
the current column number to one and adds one to the current line number;
each skipping of a page terminator sets the current column and line
numbers to one and adds one to the current page number. Similar
considerations apply to the procedures Get_Line, Put_Line, and Set_Col.
4. Several Get and Put procedures, for numeric and enumeration types, have
format parameters which specify field lengths; these parameters are of
the nonnegative subtype Field of the type Integer.
5. Input-output of enumeration values uses the syntax of the corresponding
lexical elements. Any Get procedure for an enumeration type begins by
skipping any leading blanks, or line or page terminators. Get procedures
for numeric or enumeration types start by skipping leading blanks, where
a blank is defined as a space or a horizontal tabulation character. Next,
characters are input only so long as the sequence input is an initial
sequence of an identifier or of a character literal (in particular, input
ceases when a line terminator is encountered). The character or line
terminator that causes input to cease remains available for subsequent
input.
6. For a numeric type, the Get procedures have a format parameter called
Width. If the value given for this parameter is zero, the Get procedure
proceeds in the same manner as for enumeration types, but using the
syntax of numeric literals instead of that of enumeration literals. If a
nonzero value is given, then exactly Width characters are input, or the
characters up to a line terminator, whichever comes first; any skipped
leading blanks are included in the count. The syntax used for numeric
literals is an extended syntax that allows a leading sign (but no
intervening blanks, or line or page terminators) and that also allows
(for real types) an integer literal as well as forms that have digits
only before the point or only after the point.
7. Any Put procedure, for an item of a numeric or an enumeration type,
outputs the value of the item as a numeric literal, identifier, or
character literal, as appropriate. This is preceded by leading spaces if
required by the format parameters Width or Fore (as described in later
subclauses), and then a minus sign for a negative value; for an
enumeration type, the spaces follow instead of leading. The format given
for a Put procedure is overridden if it is insufficiently wide, by using
the minimum needed width.
8. Two further cases arise for Put procedures for numeric and enumeration
types, if the line length of the specified output file is bounded (that
is, if it does not have the conventional value zero). If the number of
characters to be output does not exceed the maximum line length, but is
such that they cannot fit on the current line, starting from the current
column, then (in effect) New_Line is called (with a spacing of one)
before output of the item. Otherwise, if the number of characters exceeds
the maximum line length, then the exception Layout_Error is propagated
and nothing is output.
9. The exception Status_Error is propagated by any of the procedures Get,
Get_Line, Put, and Put_Line if the file to be used is not open. The
exception Mode_Error is propagated by the procedures Get and Get_Line if
the mode of the file to be used is not In_File; and by the procedures Put
and Put_Line, if the mode is not Out_File or Append_File.
10. The exception End_Error is propagated by a Get procedure if an attempt is
made to skip a file terminator. The exception Data_Error is propagated by
a Get procedure if the sequence finally input is not a lexical element
corresponding to the type, in particular if no characters were input; for
this test, leading blanks are ignored; for an item of a numeric type,
when a sign is input, this rule applies to the succeeding numeric
literal. The exception Layout_Error is propagated by a Put procedure that
outputs to a parameter of type String, if the length of the actual string
is insufficient for the output of the item.
Examples
11. In the examples, here and in A.10.8, and A.10.9, the string quotes and
the lower case letter b are not transferred: they are shown only to
reveal the layout and spaces.
12.
N : Integer;
┬╖┬╖┬╖
Get(N);
13.
-- Characters at input Sequence input Value of N
-- bb-12535b -12535 -12535
-- bb12_535e1b 12_535e1 125350
-- bb12_535e; 12_535e (none) Data_Error raised
14. Example of overridden width parameter:
15.
Put(Item => -23, Width => 2); -- "-23"
ΓòÉΓòÉΓòÉ 17.10.7. Input-Output of Characters and Strings ΓòÉΓòÉΓòÉ
Static Semantics
1. For an item of type Character the following procedures are provided:
2.
procedure Get(File : in File_Type; Item : out Character);
procedure Get(Item : out Character);
a. After skipping any line terminators and any page terminators, reads
the next character from the specified input file and returns the
value of this character in the out parameter Item.
b. The exception End_Error is propagated if an attempt is made to skip
a file terminator.
1.
procedure Put(File : in File_Type; Item : in Character);
procedure Put(Item : in Character);
a. If the line length of the specified output file is bounded (that is,
does not have the conventional value zero), and the current column
number exceeds it, has the effect of calling New_Line with a spacing
of one. Then, or otherwise, outputs the given character to the file.
1.
procedure Look_Ahead (File : in File_Type;
Item : out Character;
End_Of_Line : out Boolean);
procedure Look_Ahead (Item : out Character;
End_Of_Line : out Boolean);
a. Mode_Error is propagated if the mode of the file is not In_File.
Sets End_Of_Line to True if at end of line, including if at end of
page or at end of file; in each of these cases the value of Item is
not specified. Otherwise End_Of_Line is set to False and Item is set
to the the next character (without consuming it) from the file.
1.
procedure Get_Immediate(File : in File_Type;
Item : out Character);
procedure Get_Immediate(Item : out Character);
a. Reads the next character, either control or graphic, from the
specified File or the default input file. Mode_Error is propagated
if the mode of the file is not In_File. End_Error is propagated if
at the end of the file. The current column, line and page numbers
for the file are not affected.
1.
procedure Get_Immediate(File : in File_Type;
Item : out Character;
Available : out Boolean);
procedure Get_Immediate(Item : out Character;
Available : out Boolean);
a. If a character, either control or graphic, is available from the
specified File or the default input file, then the character is
read; Available is True and Item contains the value of this
character. If a character is not available, then Available is False
and the value of Item is not specified. Mode_Error is propagated if
the mode of the file is not In_File. End_Error is propagated if at
the end of the file. The current column, line and page numbers for
the file are not affected.
1. For an item of type String the following procedures are provided:
2.
procedure Get(File : in File_Type; Item : out String);
procedure Get(Item : out String);
a. Determines the length of the given string and attempts that number
of Get operations for successive characters of the string (in
particular, no operation is performed if the string is null).
1.
procedure Put(File : in File_Type; Item : in String);
procedure Put(Item : in String);
a. Determines the length of the given string and attempts that number
of Put operations for successive characters of the string (in
particular, no operation is performed if the string is null).
1.
procedure Get_Line(File : in File_Type;
Item : out String;
Last : out Natural);
procedure Get_Line(Item : out String; Last : out Natural);
a. Reads successive characters from the specified input file and
assigns them to successive characters of the specified string.
Reading stops if the end of the string is met. Reading also stops if
the end of the line is met before meeting the end of the string; in
this case Skip_Line is (in effect) called with a spacing of 1. The
values of characters not assigned are not specified.
b. If characters are read, returns in Last the index value such that
Item(Last) is the last character assigned (the index of the first
character assigned is Item'First). If no characters are read,
returns in Last an index value that is one less than Item'First. The
exception End_Error is propagated if an attempt is made to skip a
file terminator.
1.
procedure Put_Line(File : in File_Type; Item : in String);
procedure Put_Line(Item : in String);
a. Calls the procedure Put for the given string, and then the procedure
New_Line with a spacing of one.
Implementation Advice
1. The Get_Immediate procedures should be implemented with unbuffered input.
For a device such as a keyboard, input should be ``available'' if a key
has already been typed, whereas for a disk file, input should always be
available except at end of file. For a file associated with a
keyboard-like device, any line-editing features of the underlying
operating system should be disabled during the execution of
Get_Immediate.
NOTES
2. (26) Get_Immediate can be used to read a single key from the keyboard
``immediately''; that is, without waiting for an end of line. In a call
of Get_Immediate without the parameter Available, the caller will wait
until a character is available.
3. (27) In a literal string parameter of Put, the enclosing string bracket
characters are not output. Each doubled string bracket character in the
enclosed string is output as a single string bracket character, as a
consequence of the rule for string literals, see 2.6.
4. (28) A string read by Get or written by Put can extend over several
lines. An implementation is allowed to assume that certain external files
do not contain page terminators, in which case Get_Line and Skip_Line can
return as soon as a line terminator is read.
ΓòÉΓòÉΓòÉ 17.10.8. Input-Output for Integer Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The following procedures are defined in the generic packages Integer_IO
and Modular_IO, which have to be instantiated for the appropriate signed
integer or modular type respectively (indicated by Num in the
specifications).
2. Values are output as decimal or based literals, without low line
characters or exponent, and, for Integer_IO, preceded by a minus sign if
negative. The format (which includes any leading spaces and minus sign)
can be specified by an optional field width parameter. Values of widths
of fields in output formats are of the nonnegative integer subtype Field.
Values of bases are of the integer subtype Number_Base.
3.
subtype Number_Base is Integer range 2 ┬╖┬╖ 16;
4. The default field width and base to be used by output procedures are
defined by the following variables that are declared in the generic
packages Integer_IO and Modular_IO:
5.
Default_Width : Field := Num'Width;
Default_Base : Number_Base := 10;
6. The following procedures are provided:
7.
procedure Get(File : in File_Type;
Item : out Num;
Width : in Field := 0);
procedure Get(Item : out Num; Width : in Field := 0);
a. If the value of the parameter Width is zero, skips any leading
blanks, line terminators, or page terminators, then reads a plus
sign if present or (for a signed type only) a minus sign if present,
then reads the longest possible sequence of characters matching the
syntax of a numeric literal without a point. If a nonzero value of
Width is supplied, then exactly Width characters are input, or the
characters (possibly none) up to a line terminator, whichever comes
first; any skipped leading blanks are included in the count.
b. Returns, in the parameter Item, the value of type Num that
corresponds to the sequence input.
c. 10 The exception Data_Error is propagated if the sequence of
characters read does not form a legal integer literal or if the
value obtained is not of the subtype Num (for Integer_IO) or is not
in the base range of Num (for Modular_IO).
1.
procedure Put(File : in File_Type;
Item : in Num;
Width : in Field := Default_Width;
Base : in Number_Base := Default_Base);
procedure Put(Item : in Num;
Width : in Field := Default_Width;
Base : in Number_Base := Default_Base);
a. Outputs the value of the parameter Item as an integer literal, with
no low lines, no exponent, and no leading zeros (but a single zero
for the value zero), and a preceding minus sign for a negative
value.
b. If the resulting sequence of characters to be output has fewer than
Width characters, then leading spaces are first output to make up
the difference.
c. Uses the syntax for decimal literal if the parameter Base has the
value ten (either explicitly or through Default_Base); otherwise,
uses the syntax for based literal, with any letters in upper case.
1.
procedure Get(From : in String;
Item : out Num;
Last : out Positive);
a. Reads an integer value from the beginning of the given string,
following the same rules as the Get procedure that reads an integer
value from a file, but treating the end of the string as a file
terminator. Returns, in the parameter Item, the value of type Num
that corresponds to the sequence input. Returns in Last the index
value such that From(Last) is the last character read.
b. The exception Data_Error is propagated if the sequence input does
not have the required syntax or if the value obtained is not of the
subtype Num.
1.
procedure Put(To : out String;
Item : in Num;
Base : in Number_Base := Default_Base);
a. Outputs the value of the parameter Item to the given string,
following the same rule as for output to a file, using the length of
the given string as the value for Width.
1. Integer_Text_IO is a library package that is a nongeneric equivalent to
Text_IO.Integer_IO for the predefined type Integer:
2.
with Ada.Text_IO;
package Ada.Integer_Text_IO is new Ada.Text_IO.Integer_IO(Integer);
3. For each predefined signed integer type, a nongeneric equivalent to
Text_IO.Integer_IO is provided, with names such as
Ada.Long_Integer_Text_IO.
Implementation Permissions
4. The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined
type.
NOTES
5. (29) For Modular_IO, execution of Get propagates Data_Error if the
sequence of characters read forms an integer literal outside the range
0┬╖┬╖Num'Last.
Examples
1.
package Int_IO is new Integer_IO(Small_Int); use Int_IO;
-- default format used at instantiation,
-- Default_Width = 4, Default_Base = 10
2.
Put(126); -- "b126"
Put(-126, 7); -- "bbb-126"
Put(126, Width => 13, Base => 2); -- "bbb2#1111110#"
ΓòÉΓòÉΓòÉ 17.10.9. Input-Output for Real Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The following procedures are defined in the generic packages Float_IO,
Fixed_IO, and Decimal_IO, which have to be instantiated for the
appropriate floating point, ordinary fixed point, or decimal fixed point
type respectively (indicated by Num in the specifications).
2. Values are output as decimal literals without low line characters. The
format of each value output consists of a Fore field, a decimal point, an
Aft field, and (if a nonzero Exp parameter is supplied) the letter E and
an Exp field. The two possible formats thus correspond to:
3.
Fore . Aft
4. and to:
5.
Fore . Aft E Exp
6. without any spaces between these fields. The Fore field may include
leading spaces, and a minus sign for negative values. The Aft field
includes only decimal digits (possibly with trailing zeros). The Exp
field includes the sign (plus or minus) and the exponent (possibly with
leading zeros).
7. For floating point types, the default lengths of these fields are defined
by the following variables that are declared in the generic package
Float_IO:
8.
Default_Fore : Field := 2;
Default_Aft : Field := Num'Digits-1;
Default_Exp : Field := 3;
9. For ordinary or decimal fixed point types, the default lengths of these
fields are defined by the following variables that are declared in the
generic packages Fixed_IO and Decimal_IO, respectively:
10.
Default_Fore : Field := Num'Fore;
Default_Aft : Field := Num'Aft;
Default_Exp : Field := 0;
11. The following procedures are provided:
12.
procedure Get(File : in File_Type;
Item : out Num;
Width : in Field := 0);
procedure Get(Item : out Num; Width : in Field := 0);
a. If the value of the parameter Width is zero, skips any leading
blanks, line terminators, or page terminators, then reads the
longest possible sequence of characters matching the syntax of any
of the following (see 2.4):
1. [+|-]numeric_literal
2. [+|-]numeral.[exponent]
3. [+|-].numeral[exponent]
4. [+|-]base#based_numeral.#[exponent]
5. [+|-]base#.based_numeral#[exponent]
a. If a nonzero value of Width is supplied, then exactly Width
characters are input, or the characters (possibly none) up to a line
terminator, whichever comes first; any skipped leading blanks are
included in the count.
b. Returns in the parameter Item the value of type Num that corresponds
to the sequence input, preserving the sign (positive if none has
been specified) of a zero value if Num is a floating point type and
Num'Signed_Zeros is True.
c. The exception Data_Error is propagated if the sequence input does
not have the required syntax or if the value obtained is not of the
subtype Num.
1.
procedure Put(File : in File_Type;
Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
procedure Put(Item : in Num;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
a. Outputs the value of the parameter Item as a decimal literal with
the format defined by Fore, Aft and Exp. If the value is negative,
or if Num is a floating point type where Num'Signed_Zeros is True
and the value is a negatively signed zero, then a minus sign is
included in the integer part. If Exp has the value zero, then the
integer part to be output has as many digits as are needed to
represent the integer part of the value of Item, overriding Fore if
necessary, or consists of the digit zero if the value of Item has no
integer part.
b. If Exp has a value greater than zero, then the integer part to be
output has a single digit, which is nonzero except for the value 0.0
of Item.
c. In both cases, however, if the integer part to be output has fewer
than Fore characters, including any minus sign, then leading spaces
are first output to make up the difference. The number of digits of
the fractional part is given by Aft, or is one if Aft equals zero.
The value is rounded; a value of exactly one half in the last place
is rounded away from zero.
d. If Exp has the value zero, there is no exponent part. If Exp has a
value greater than zero, then the exponent part to be output has as
many digits as are needed to represent the exponent part of the
value of Item (for which a single digit integer part is used), and
includes an initial sign (plus or minus). If the exponent part to be
output has fewer than Exp characters, including the sign, then
leading zeros precede the digits, to make up the difference. For the
value 0.0 of Item, the exponent has the value zero.
1.
procedure Get(From : in String; Item : out Num; Last : out Positive);
a. Reads a real value from the beginning of the given string, following
the same rule as the Get procedure that reads a real value from a
file, but treating the end of the string as a file terminator.
Returns, in the parameter Item, the value of type Num that
corresponds to the sequence input. Returns in Last the index value
such that From(Last) is the last character read.
b. The exception Data_Error is propagated if the sequence input does
not have the required syntax, or if the value obtained is not of the
subtype Num.
1.
procedure Put(To : out String;
Item : in Num;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
a. Outputs the value of the parameter Item to the given string,
following the same rule as for output to a file, using a value for
Fore such that the sequence of characters output exactly fills the
string, including any leading spaces.
1. Float_Text_IO is a library package that is a nongeneric equivalent to
Text_IO.Float_IO for the predefined type Float:
2.
with Ada.Text_IO;
package Ada.Float_Text_IO is new Ada.Text_IO.Float_IO(Float);
3. For each predefined floating point type, a nongeneric equivalent to
Text_IO.Float_IO is provided, with names such as Ada.Long_Float_Text_IO.
Implementation Permissions
4. An implementation may extend Get and Put for floating point types to
support special values such as infinities and NaNs.
5. The implementation of Put need not produce an output value with greater
accuracy than is supported for the base subtype. The additional accuracy,
if any, of the value produced by Put when the number of requested digits
in the integer and fractional parts exceeds the required accuracy is
implementation defined.
6. The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined
type.
NOTES
7. (30) For an item with a positive value, if output to a string exactly
fills the string without leading spaces, then output of the corresponding
negative value will propagate Layout_Error.
8. (31) The rules for the Value attribute, see 3.5, and the rules for Get
are based on the same set of formats.
Examples
1.
package Real_IO is new Float_IO(Real); use Real_IO;
-- default format used at instantiation, Default_Exp = 3
2.
X : Real := -123.4567; -- digits 8 (see 3.5.7)
3.
Put(X); -- default format "-1.2345670E+02"
Put(X, Fore => 5, Aft => 3, Exp => 2); -- "bbb-1.235E+2"
Put(X, 5, 3, 0); -- "b-123.457"
ΓòÉΓòÉΓòÉ 17.10.10. Input-Output for Enumeration Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The following procedures are defined in the generic package
Enumeration_IO, which has to be instantiated for the appropriate
enumeration type (indicated by Enum in the specification).
2. Values are output using either upper or lower case letters for
identifiers. This is specified by the parameter Set, which is of the
enumeration type Type_Set.
3.
type Type_Set is (Lower_Case, Upper_Case);
4. The format (which includes any trailing spaces) can be specified by an
optional field width parameter. The default field width and letter case
are defined by the following variables that are declared in the generic
package Enumeration_IO:
5.
Default_Width : Field := 0;
Default_Setting : Type_Set := Upper_Case;
6. The following procedures are provided:
7.
procedure Get(File : in File_Type; Item : out Enum);
procedure Get(Item : out Enum);
a. After skipping any leading blanks, line terminators, or page
terminators, reads an identifier according to the syntax of this
lexical element (lower and upper case being considered equivalent),
or a character literal according to the syntax of this lexical
element (including the apostrophes). Returns, in the parameter Item,
the value of type Enum that corresponds to the sequence input.
b. The exception Data_Error is propagated if the sequence input does
not have the required syntax, or if the identifier or character
literal does not correspond to a value of the subtype Enum.
1.
procedure Put(File : in File_Type;
Item : in Enum;
Width : in Field := Default_Width;
Set : in Type_Set := Default_Setting);
procedure Put(Item : in Enum;
Width : in Field := Default_Width;
Set : in Type_Set := Default_Setting);
a. Outputs the value of the parameter Item as an enumeration literal
(either an identifier or a character literal). The optional
parameter Set indicates whether lower case or upper case is used for
identifiers; it has no effect for character literals. If the
sequence of characters produced has fewer than Width characters,
then trailing spaces are finally output to make up the difference.
If Enum is a character type, the sequence of characters produced is
as for Enum'Image(Item), as modified by the Width and Set
parameters.
1.
procedure Get(From : in String;
Item : out Enum;
Last : out Positive);
a. Reads an enumeration value from the beginning of the given string,
following the same rule as the Get procedure that reads an
enumeration value from a file, but treating the end of the string as
a file terminator. Returns, in the parameter Item, the value of type
Enum that corresponds to the sequence input. Returns in Last the
index value such that From(Last) is the last character read.
b. The exception Data_Error is propagated if the sequence input does
not have the required syntax, or if the identifier or character
literal does not correspond to a value of the subtype Enum.
1.
procedure Put(To : out String;
Item : in Enum;
Set : in Type_Set := Default_Setting);
a. Outputs the value of the parameter Item to the given string,
following the same rule as for output to a file, using the length of
the given string as the value for Width.
1. Although the specification of the generic package Enumeration_IO would
allow instantiation for an float type, this is not the intended purpose
of this generic package, and the effect of such instantiations is not
defined by the language.
NOTES
2. (32) There is a difference between Put defined for characters, and for
enumeration values. Thus
3.
Ada.Text_IO.Put('A'); -- outputs the character A
4.
package Char_IO is new Ada.Text_IO.Enumeration_IO(Character);
Char_IO.Put('A'); -- outputs the character 'A', between apostrophes
5. (33) The type Boolean is an enumeration type, hence Enumeration_IO can be
instantiated for this type.
ΓòÉΓòÉΓòÉ 17.11. Wide Text Input-Output ΓòÉΓòÉΓòÉ
1. The package Wide_Text_IO provides facilities for input and output in
human-readable form. Each file is read or written sequentially, as a
sequence of wide characters grouped into lines, and as a sequence of
lines grouped into pages.
Static Semantics
2. The specification of package Wide_Text_IO is the same as that for
Text_IO, except that in each Get, Look_Ahead, Get_Immediate, Get_Line,
Put, and Put_Line procedure, any occurrence of Character is replaced by
Wide_Character, and any occurrence of String is replaced by Wide_String.
3. Nongeneric equivalents of Wide_Text_IO.Integer_IO and
Wide_Text_IO.Float_IO are provided (as for Text_IO) for each predefined
numeric type, with names such as Ada.Integer_Wide_Text_IO,
Ada.Long_Integer_Wide_Text_IO, Ada.Float_Wide_Text_IO,
Ada.Long_Float_Wide_Text_IO.
ΓòÉΓòÉΓòÉ 17.12. Stream Input-Output ΓòÉΓòÉΓòÉ
1. The packages Streams.Stream_IO, Text_IO.Text_Streams, and
Wide_Text_IO.Text_Streams provide stream-oriented operations on files.
A.12.1 The Package Streams.Stream_IO
A.12.2 The Package Text_IO.Text_Streams
A.12.3 The Package Wide_Text_IO.Text_Streams
ΓòÉΓòÉΓòÉ 17.12.1. The Package Streams.Stream_IO ΓòÉΓòÉΓòÉ
1. The subprograms in the child package Streams.Stream_IO provide control
over stream files. Access to a stream file is either sequential, via a
call on Read or Write to transfer an array of stream elements, or
positional (if supported by the implementation for the given file), by
specifying a relative index for an element. Since a stream file can be
converted to a Stream_Access value, calling stream-oriented attribute
subprograms of different element types with the same Stream_Access value
provides heterogeneous input-output. See 13.13 for a general discussion
of streams.
Static Semantics
2. The library package Streams.Stream_IO has the following declaration:
3.
with Ada.IO_Exceptions;
package Ada.Streams.Stream_IO is
4.
type Stream_Access is access all Root_Stream_Type'Class;
5.
type File_Type is limited private;
6.
type File_Mode is (In_File, Out_File, Append_File);
7.
type Count is range 0 ┬╖┬╖ implementation-defined;
subtype Positive_Count is Count range 1 ┬╖┬╖ Count'Last;
-- Index into file, in stream elements.
8.
procedure Create (File : in out File_Type;
Mode : in File_Mode := Out_File;
Name : in String := "";
Form : in String := "");
9.
procedure Open (File : in out File_Type;
Mode : in File_Mode;
Name : in String;
Form : in String := "");
10.
procedure Close (File : in out File_Type);
procedure Delete (File : in out File_Type);
procedure Reset (File : in out File_Type; Mode : in File_Mode);
procedure Reset (File : in out File_Type);
11.
function Mode (File : in File_Type) return File_Mode;
function Name (File : in File_Type) return String;
function Form (File : in File_Type) return String;
12.
function Is_Open (File : in File_Type) return Boolean;
function End_Of_File (File : in File_Type) return Boolean;
13.
function Stream (File : in File_Type) return Stream_Access;
-- Return stream access for use with T'Input and T'Output
1.
-- Read array of stream elements from file
procedure Read (File : in File_Type;
Item : out Stream_Element_Array;
Last : out Stream_Element_Offset;
From : in Positive_Count);
2.
procedure Read (File : in File_Type;
Item : out Stream_Element_Array;
Last : out Stream_Element_Offset);
1.
-- Write array of stream elements into file
procedure Write (File : in File_Type;
Item : in Stream_Element_Array;
To : in Positive_Count);
2.
procedure Write (File : in File_Type;
Item : in Stream_Element_Array);
1.
-- Operations on position within file
2.
procedure Set_Index(File : in File_Type;
To : in Positive_Count);
3.
function Index(File : in File_Type) return Positive_Count;
function Size (File : in File_Type) return Count;
4.
procedure Set_Mode(File : in out File_Type;
Mode : in File_Mode);
5.
procedure Flush(File : in out File_Type);
6.
-- exceptions
Status_Error : exception renames IO_Exceptions.Status_Error;
Mode_Error : exception renames IO_Exceptions.Mode_Error;
Name_Error : exception renames IO_Exceptions.Name_Error;
Use_Error : exception renames IO_Exceptions.Use_Error;
Device_Error : exception renames IO_Exceptions.Device_Error;
End_Error : exception renames IO_Exceptions.End_Error;
Data_Error : exception renames IO_Exceptions.Data_Error;
7.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Streams.Stream_IO;
8. The subprograms Create, Open, Close, Delete, Reset, Mode, Name, Form,
Is_Open, and End_of_File have the same effect as the corresponding
subprograms in Sequential_IO, see A.8.2.
9. The Stream function returns a Stream_Access result from a File_Type
object, thus allowing the stream-oriented attributes Read, Write, Input,
and Output to be used on the same file for multiple types.
10. The procedures Read and Write are equivalent to the corresponding
operations in the package Streams. Read propagates Mode_Error if the mode
of File is not In_File. Write propagates Mode_Error if the mode of File
is not Out_File or Append_File. The Read procedure with a Positive_Count
parameter starts reading at the specified index. The Write procedure with
a Positive_Count parameter starts writing at the specified index.
11. The Index function returns the current file index, as a count (in stream
elements) from the beginning of the file. The position of the first
element in the file is 1.
12. The Set_Index procedure sets the current index to the specified value.
13. If positioning is not supported for the given file, then a call of Index
or Set_Index propagates Use_Error. Similarly, a call of Read or Write
with a Positive_Count parameter propagates Use_Error.
14. The Size function returns the current size of the file, in stream
elements.
15. The Set_Mode procedure changes the mode of the file. If the new mode is
Append_File, the file is positioned to its end; otherwise, the position
in the file is unchanged.
16. The Flush procedure synchronizes the external file with the internal file
(by flushing any internal buffers) without closing the file or changing
the position. Mode_Error is propagated if the mode of the file is
In_File.
ΓòÉΓòÉΓòÉ 17.12.2. The Package Text_IO.Text_Streams ΓòÉΓòÉΓòÉ
1. The package Text_IO.Text_Streams provides a function for treating a text
file as a stream.
Static Semantics
2. The library package Text_IO.Text_Streams has the following declaration:
3.
with Ada.Streams;
package Ada.Text_IO.Text_Streams is
type Stream_Access is access all Streams.Root_Stream_Type'Class;
4.
function Stream (File : in File_Type) return Stream_Access;
end Ada.Text_IO.Text_Streams;
5. The Stream function has the same effect as the corresponding function in
Streams.Stream_IO.
NOTES
6. (34) The ability to obtain a stream for a text file allows Current_Input,
Current_Output, and Current_Error to be processed with the functionality
of streams, including the mixing of text and binary input-output, and the
mixing of binary input-output for different types.
7. (35) Performing operations on the stream associated with a text file does
not affect the column, line, or page counts.
ΓòÉΓòÉΓòÉ 17.12.3. The Package Wide_Text_IO.Text_Streams ΓòÉΓòÉΓòÉ
1. The package Wide_Text_IO.Text_Streams provides a function for treating a
wide text file as a stream.
Static Semantics
2. The library package Wide_Text_IO.Text_Streams has the following
declaration:
3.
with Ada.Streams;
package Ada.Wide_Text_IO.Text_Streams is
type Stream_Access is access all Streams.Root_Stream_Type'Class;
4.
function Stream (File : in File_Type) return Stream_Access;
end Ada.Wide_Text_IO.Text_Streams;
5. The Stream function has the same effect as the corresponding function in
Streams.Stream_IO.
ΓòÉΓòÉΓòÉ 17.13. Exceptions in Input-Output ΓòÉΓòÉΓòÉ
1. The package IO_Exceptions defines the exceptions needed by the predefined
input-output packages.
Static Semantics
2. The library package IO_Exceptions has the following declaration:
3.
package Ada.IO_Exceptions is
pragma Pure(IO_Exceptions);
4.
Status_Error : exception;
Mode_Error : exception;
Name_Error : exception;
Use_Error : exception;
Device_Error : exception;
End_Error : exception;
Data_Error : exception;
Layout_Error : exception;
5.
end Ada.IO_Exceptions;
6. If more than one error condition exists, the corresponding exception that
appears earliest in the following list is the one that is propagated.
7. The exception Status_Error is propagated by an attempt to operate upon a
file that is not open, and by an attempt to open a file that is already
open.
8. The exception Mode_Error is propagated by an attempt to read from, or
test for the end of, a file whose current mode is Out_File or
Append_File, and also by an attempt to write to a file whose current mode
is In_File. In the case of Text_IO, the exception Mode_Error is also
propagated by specifying a file whose current mode is Out_File or
Append_File in a call of Set_Input, Skip_Line, End_Of_Line, Skip_Page, or
End_Of_Page; and by specifying a file whose current mode is In_File in a
call of Set_Output, Set_Line_Length, Set_Page_Length, Line_Length,
Page_Length, New_Line, or New_Page.
9. The exception Name_Error is propagated by a call of Create or Open if the
string given for the parameter Name does not allow the identification of
an external file. For example, this exception is propagated if the string
is improper, or, alternatively, if either none or more than one external
file corresponds to the string.
10. The exception Use_Error is propagated if an operation is attempted that
is not possible for reasons that depend on characteristics of the
external file. For example, this exception is propagated by the procedure
Create, among other circumstances, if the given mode is Out_File but the
form specifies an input only device, if the parameter Form specifies
invalid access rights, or if an external file with the given name already
exists and overwriting is not allowed.
11. The exception Device_Error is propagated if an input-output operation
cannot be completed because of a malfunction of the underlying system.
12. The exception End_Error is propagated by an attempt to skip (read past)
the end of a file.
13. The exception Data_Error can be propagated by the procedure Read (or by
the Read attribute) if the element read cannot be interpreted as a value
of the required subtype. This exception is also propagated by a procedure
Get (defined in the package Text_IO) if the input character sequence
fails to satisfy the required syntax, or if the value input does not
belong to the range of the required subtype.
14. The exception Layout_Error is propagated (in text input-output) by Col,
Line, or Page if the value returned exceeds Count'Last. The exception
Layout_Error is also propagated on output by an attempt to set column or
line numbers in excess of specified maximum line or page lengths,
respectively (excluding the unbounded cases). It is also propagated by an
attempt to Put too many characters to a string.
Documentation Requirements
15. The implementation shall document the conditions under which Name_Error,
Use_Error and Device_Error are propagated.
Implementation Permissions
16. If the associated check is too complex, an implementation need not
propagate Data_Error as part of a procedure Read (or the Read attribute)
if the value read cannot be interpreted as a value of the required
subtype.
Erroneous Execution
17. If the element read by the procedure Read (or by the Read attribute)
cannot be interpreted as a value of the required subtype, but this is not
detected and Data_Error is not propagated, then the resulting value can
be abnormal, and subsequent references to the value can lead to erroneous
execution, as explained in 13.9.1.
ΓòÉΓòÉΓòÉ 17.14. File Sharing ΓòÉΓòÉΓòÉ
Dynamic Semantics
1. It is not specified by the language whether the same external file can be
associated with more than one file object. If such sharing is supported
by the implementation, the following effects are defined:
a. Operations on one text file object do not affect the column, line,
and page numbers of any other file object.
b. Standard_Input and Standard_Output are associated with distinct
external files, so operations on one of these files cannot affect
operations on the other file. In particular, reading from
Standard_Input does not affect the current page, line, and column
numbers for Standard_Output, nor does writing to Standard_Output
affect the current page, line, and column numbers for
Standard_Input.
c. For direct and stream files, the current index is a property of each
file object; an operation on one file object does not affect the
current index of any other file object.
d. For direct and stream files, the current size of the file is a
property of the external file.
All other effects are identical.
ΓòÉΓòÉΓòÉ 17.15. The Package Command_Line ΓòÉΓòÉΓòÉ
1. The package Command_Line allows a program to obtain the values of its
arguments and to set the exit status code to be returned on normal
termination.
Static Semantics
2. The library package Ada.Command_Line has the following declaration:
3.
package Ada.Command_Line is
pragma Preelaborate(Command_Line);
4.
function Argument_Count return Natural;
5.
function Argument (Number : in Positive) return String;
6.
function Command_Name return String;
7.
type Exit_Status is implementation-defined integer type;
8.
Success : constant Exit_Status;
Failure : constant Exit_Status;
9.
procedure Set_Exit_Status (Code : in Exit_Status);
10.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Command_Line;
11.
function Argument_Count return Natural;
a. If the external execution environment supports passing arguments to
a program, then Argument_Count returns the number of arguments
passed to the program invoking the function. Otherwise it returns 0.
The meaning of ``number of arguments'' is implementation defined.
1.
function Argument (Number : in Positive) return String;
a. If the external execution environment supports passing arguments to
a program, then Argument returns an implementation-defined value
corresponding to the argument at relative position Number. If Number
is outside the range 1┬╖┬╖Argument_Count, then Constraint_Error is
propagated.
1.
function Command_Name return String;
a. If the external execution environment supports passing arguments to
a program, then Command_Name returns an implementation-defined value
corresponding to the name of the command invoking the program;
otherwise Command_Name returns the null string.
b. The type Exit_Status represents the range of exit status values
supported by the external execution environment. The constants
Success and Failure correspond to success and failure, respectively.
1.
procedure Set_Exit_Status (Code : in Exit_Status);
a. If the external execution environment supports returning an exit
status from a program, then Set_Exit_Status sets Code as the status.
Normal termination of a program returns as the exit status the value
most recently set by Set_Exit_Status, or, if no such value has been
set, then the value Success. If a program terminates abnormally, the
status set by Set_Exit_Status is ignored, and an
implementation-defined exit status value is set.
b. If the external execution environment does not support returning an
exit value from a program, then Set_Exit_Status does nothing.
Implementation Permissions
1. An alternative declaration is allowed for package Command_Line if
different functionality is appropriate for the external execution
environment.
NOTES
2. (36) Argument_Count, Argument, and Command_Name correspond to the C
language's argc, argv[n] (for n>0) and argv[0], respectively.
ΓòÉΓòÉΓòÉ 18. Interface to Other Languages (normative) ΓòÉΓòÉΓòÉ
1. This Annex describes features for writing mixed-language programs.
General interface support is presented first; then specific support for
C, COBOL, and Fortran is defined, in terms of language interface packages
for each of these languages.
B.1 Interfacing Pragmas
B.2 The Package Interfaces
B.3 Interfacing with C
B.4 Interfacing with COBOL
B.5 Interfacing with Fortran --- The Detailed Node
Listing ---
B.1 Interfacing Pragmas
B.2 The Package Interfaces
B.3 Interfacing with C
B.3.1 The Package Interfaces.C.Strings
B.3.2 The Generic Package Interfaces.C.Pointers
B.4 Interfacing with COBOL
B.5 Interfacing with Fortran
ΓòÉΓòÉΓòÉ 18.1. Interfacing Pragmas ΓòÉΓòÉΓòÉ
1. A pragma Import is used to import an entity defined in a foreign language
into an Ada program, thus allowing a foreign-language subprogram to be
called from Ada, or a foreign-language variable to be accessed from Ada.
In contrast, a pragma Export is used to export an Ada entity to a foreign
language, thus allowing an Ada subprogram to be called from a foreign
language, or an Ada object to be accessed from a foreign language. The
pragmas Import and Export are intended primarily for objects and
subprograms, although implementations are allowed to support other
entities.
2. A pragma Convention is used to specify that an Ada entity should use the
conventions of another language. It is intended primarily for types and
``callback'' subprograms. For example, ``pragma Convention(Fortran,
Matrix);'' implies that Matrix should be represented according to the
conventions of the supported Fortran implementation, namely column-major
order.
3. A pragma Linker_Options is used to specify the system linker parameters
needed when a given compilation unit is included in a partition.
Syntax
4. An interfacing pragma is a representation pragma that is one of the
pragmas Import, Export, or Convention. Their forms, together with that of
the related pragma Linker_Options, are as follows:
5.
pragma Import
([Convention =>] convention_identifier,
[Entity =>] local_name [,
[External_Name =>] string_expression] [,
[Link_Name =>] string_expression]);
6.
pragma Export
([Convention =>] convention_identifier,
[Entity =>] local_name [,
[External_Name =>] string_expression] [,
[Link_Name =>] string_expression]);
7.
pragma Convention
([Convention =>] convention_identifier,
[Entity =>] local_name);
8.
pragma Linker_Options(string_expression);
a. A pragma Linker_Options is allowed only at the place of a
declarative_item.
Name Resolution Rules
1. The expected type for a string_expression in an interfacing pragma or in
pragma Linker_Options is String.
Legality Rules
2. The convention_identifier of an interfacing pragma shall be the name of a
convention. The convention names are implementation defined, except for
certain language-defined ones, such as Ada and Intrinsic, as explained in
6.3.1: ``Conformance Rules''. Additional convention names generally
represent the calling conventions of foreign languages, language
implementations, or specific run-time models. The convention of a
callable entity is its calling convention.
3. If L is a convention_identifier for a language, then a type T is said to
be compatible with convention L, (alternatively, is said to be an
L-compatible type) if any of the following conditions are met:
a. T is declared in a language interface package corresponding to L and
is defined to be L-compatible, see B.3, B.3.1, B.3.2, B.4 and B.5
b. Convention L has been specified for T in a pragma Convention, and T
is eligible for convention L; that is:
1. T is an array type with either an unconstrained or
statically-constrained first subtype, and its component type is
L-compatible,
2. T is a record type that has no discriminants and that only has
components with statically-constrained subtypes, and each
component type is L-compatible,
3. T is an access-to-object type, and its designated type is
L-compatible,
4. T is an access-to-subprogram type, and its designated profile's
parameter and result types are all L-compatible.
a. T is derived from an L-compatible type,
b. The implementation permits T as an L-compatible type.
1. If pragma Convention applies to a type, then the type shall either be
compatible with or eligible for the convention specified in the pragma.
2. A pragma Import shall be the completion of a declaration. Notwithstanding
any rule to the contrary, a pragma Import may serve as the completion of
any kind of (explicit) declaration if supported by an implementation for
that kind of declaration. If a completion is a pragma Import, then it
shall appear in the same declarative_part, package_specification,
task_definition or protected_definition as the declaration. For a library
unit, it shall appear in the same compilation, before any subsequent
compilation_units other than pragmas. If the local_name denotes more than
one entity, then the pragma Import is the completion of all of them.
3. An entity specified as the Entity argument to a pragma Import (or pragma
Export) is said to be imported (respectively, exported).
4. The declaration of an imported object shall not include an explicit
initialization expression. Default initializations are not performed.
5. The type of an imported or exported object shall be compatible with the
convention specified in the corresponding pragma.
6. For an imported or exported subprogram, the result and parameter types
shall each be compatible with the convention specified in the
corresponding pragma.
7. The external name and link name string_expressions of a pragma Import or
Export, and the string_expression of a pragma Linker_Options, shall be
static.
Static Semantics
8. Import, Export, and Convention pragmas are representation pragmas that
specify the convention aspect of representation. In addition, Import and
Export pragmas specify the imported and exported aspects of
representation, respectively.
9. An interfacing pragma is a program unit pragma when applied to a program
unit, see 10.1.5.
10. An interfacing pragma defines the convention of the entity denoted by the
local_name. The convention represents the calling convention or
representation convention of the entity. For an access-to-subprogram
type, it represents the calling convention of designated subprograms. In
addition:
a. A pragma Import specifies that the entity is defined externally
(that is, outside the Ada program).
b. A pragma Export specifies that the entity is used externally.
c. A pragma Import or Export optionally specifies an entity's external
name, link name, or both.
1. An external name is a string value for the name used by a foreign
language program either for an entity that an Ada program imports, or for
referring to an entity that an Ada program exports.
2. A link name is a string value for the name of an exported or imported
entity, based on the conventions of the foreign language's compiler in
interfacing with the system's linker tool.
3. The meaning of link names is implementation defined. If neither a link
name nor the Address attribute of an imported or exported entity is
specified, then a link name is chosen in an implementation-defined
manner, based on the external name if one is specified.
4. Pragma Linker_Options has the effect of passing its string argument as a
parameter to the system linker (if one exists), if the immediately
enclosing compilation unit is included in the partition being linked. The
interpretation of the string argument, and the way in which the string
arguments from multiple Linker_Options pragmas are combined, is
implementation defined.
Dynamic Semantics
5. Notwithstanding what this International Standard says elsewhere, the
elaboration of a declaration denoted by the local_name of a pragma Import
does not create the entity. Such an elaboration has no other effect than
to allow the defining name to denote the external entity.
Implementation Advice
6. If an implementation supports pragma Export to a given language, then it
should also allow the main subprogram to be written in that language. It
should support some mechanism for invoking the elaboration of the Ada
library units included in the system, and for invoking the finalization
of the environment task. On typical systems, the recommended mechanism is
to provide two subprograms whose link names are "adainit" and "adafinal".
Adainit should contain the elaboration code for library units. Adafinal
should contain the finalization code. These subprograms should have no
effect the second and subsequent time they are called.
7. Automatic elaboration of preelaborated packages should be provided when
pragma Export is supported.
8. For each supported convention L other than Intrinsic, an implementation
should support Import and Export pragmas for objects of L-compatible
types and for subprograms, and pragma Convention for L-eligible types and
for subprograms, presuming the other language has corresponding features.
Pragma Convention need not be supported for scalar types.
NOTES
9. (1) Implementations may place restrictions on interfacing pragmas; for
example, requiring each exported entity to be declared at the library
level.
10. (2) A pragma Import specifies the conventions for accessing external
entities. It is possible that the actual entity is written in assembly
language, but reflects the conventions of a particular language. For
example, pragma Import(Ada, ┬╖┬╖┬╖) can be used to interface to an assembly
language routine that obeys the Ada compiler's calling conventions.
11. (3) To obtain ``call-back'' to an Ada subprogram from a foreign language
environment, pragma Convention should be specified both for the
access-to-subprogram type and the specific subprogram(s) to which 'Access
is applied.
12. (4) It is illegal to specify more than one of Import, Export, or
Convention for a given entity.
13. (5) The local_name in an interfacing pragma can denote more than one
entity in the case of overloading. Such a pragma applies to all of the
denoted entities.
14. (6) Also 13.8: ``Machine Code Insertions''.
15. (7) If both External_Name and Link_Name are specified for an Import or
Export pragma, then the External_Name is ignored.
16. (8) An interfacing pragma might result in an effect that violates Ada
semantics.
Examples
17. Example of interfacing pragmas:
18.
package Fortran_Library is
function Sqrt (X : Float) return Float;
function Exp (X : Float) return Float;
private
pragma Import(Fortran, Sqrt);
pragma Import(Fortran, Exp);
end Fortran_Library;
ΓòÉΓòÉΓòÉ 18.2. The Package Interfaces ΓòÉΓòÉΓòÉ
1. Package Interfaces is the parent of several library packages that declare
types and other entities useful for interfacing to foreign languages. It
also contains some implementation-defined types that are useful across
more than one language (in particular for interfacing to assembly
language).
Static Semantics
2. The library package Interfaces has the following skeletal declaration:
3.
package Interfaces is
pragma Pure(Interfaces);
4.
type Integer_n is range -2**(n-1) ┬╖┬╖ 2**(n-1) - 1;
-- 2's complement
5.
type Unsigned_n is mod 2**n;
6.
function Shift_Left (Value : Unsigned_n;
Amount : Natural) return Unsigned_n;
function Shift_Right (Value : Unsigned_n;
Amount : Natural) return Unsigned_n;
function Shift_Right_Arithmetic (Value : Unsigned_n;
Amount : Natural)
return Unsigned_n;
function Rotate_Left (Value : Unsigned_n;
Amount : Natural) return Unsigned_n;
function Rotate_Right (Value : Unsigned_n;
Amount : Natural) return Unsigned_n;
┬╖┬╖┬╖
end Interfaces;
Implementation Requirements
7. An implementation shall provide the following declarations in the visible
part of package Interfaces:
a. Signed and modular integer types of n bits, if supported by the
target architecture, for each n that is at least the size of a
storage element and that is a factor of the word size. The names of
these types are of the form Integer_n for the signed types, and
Unsigned_n for the modular types;
b. For each such modular type in Interfaces, shifting and rotating
subprograms as specified in the declaration of Interfaces above.
These subprograms are Intrinsic. They operate on a bit-by-bit basis,
using the binary representation of the value of the operands to
yield a binary representation for the result. The Amount parameter
gives the number of bits by which to shift or rotate. For shifting,
zero bits are shifted in, except in the case of
Shift_Right_Arithmetic, where one bits are shifted in if Value is at
least half the modulus.
c. Floating point types corresponding to each floating point format
fully supported by the hardware.
Implementation Permissions
1. An implementation may provide implementation-defined library units that
are children of Interfaces, and may add declarations to the visible part
of Interfaces in addition to the ones defined above.
2. Implementation Advice
3. For each implementation-defined convention identifier, there should be a
child package of package Interfaces with the corresponding name. This
package should contain any declarations that would be useful for
interfacing to the language (implementation) represented by the
convention. Any declarations useful for interfacing to any language on
the given hardware architecture should be provided directly in
Interfaces.
4. An implementation supporting an interface to C, COBOL, or Fortran should
provide the corresponding package or packages described in the following
clauses.
ΓòÉΓòÉΓòÉ 18.3. Interfacing with C ΓòÉΓòÉΓòÉ
1. The facilities relevant to interfacing with the C language are the
package Interfaces.C and its children; and support for the Import,
Export, and Convention pragmas with convention_identifier C.
2. The package Interfaces.C contains the basic types, constants and
subprograms that allow an Ada program to pass scalars and strings to C
functions.
Static Semantics
3. The library package Interfaces.C has the following declaration:
4.
package Interfaces.C is
pragma Pure(C);
5.
-- Declarations based on C's <limits.h>
6.
CHAR_BIT : constant := implementation-defined; -- typically 8
SCHAR_MIN : constant := implementation-defined; -- typically -128
SCHAR_MAX : constant := implementation-defined; -- typically 127
UCHAR_MAX : constant := implementation-defined; -- typically 255
7.
-- Signed and Unsigned Integers
type int is range implementation-defined;
type short is range implementation-defined;
type long is range implementation-defined;
8.
type signed_char is range SCHAR_MIN ┬╖┬╖ SCHAR_MAX;
for signed_char'Size use CHAR_BIT;
9.
type unsigned is mod implementation-defined;
type unsigned_short is mod implementation-defined;
type unsigned_long is mod implementation-defined;
10.
type unsigned_char is mod (UCHAR_MAX+1);
for unsigned_char'Size use CHAR_BIT;
11.
subtype plain_char is implementation-defined;
12.
type ptrdiff_t is range implementation-defined;
13.
type size_t is mod implementation-defined;
14.
-- Floating Point
15.
type C_float is digits implementation-defined;
16.
type double is digits implementation-defined;
17.
type long_double is digits implementation-defined;
18.
-- Characters and Strings
19.
type char is <implementation-defined character type>;
20.
nul : constant char := char'First;
21.
function To_C (Item : in Character) return char;
22.
function To_Ada (Item : in char) return Character;
23.
type char_array is array (size_t range <>) of aliased char;
pragma Pack(char_array);
for char_array'Component_Size use CHAR_BIT;
24.
function Is_Nul_Terminated (Item : in char_array) return Boolean;
25.
function To_C (Item : in String;
Append_Nul : in Boolean := True)
return char_array;
26.
function To_Ada (Item : in char_array;
Trim_Nul : in Boolean := True)
return String;
27.
procedure To_C (Item : in String;
Target : out char_array;
Count : out size_t;
Append_Nul : in Boolean := True);
28.
procedure To_Ada (Item : in char_array;
Target : out String;
Count : out Natural;
Trim_Nul : in Boolean := True);
29.
-- Wide Character and Wide String
30.
type wchar_t is implementation-defined;
31.
wide_nul : constant wchar_t := wchar_t'First;
32.
function To_C (Item : in Wide_Character) return wchar_t;
function To_Ada (Item : in wchar_t ) return Wide_Character;
33.
type wchar_array is array (size_t range <>) of aliased wchar_t;
34.
pragma Pack(wchar_array);
35.
function Is_Nul_Terminated (Item : in wchar_array)
return Boolean;
36.
function To_C (Item : in Wide_String;
Append_Nul : in Boolean := True)
return wchar_array;
37.
function To_Ada (Item : in wchar_array;
Trim_Nul : in Boolean := True)
return Wide_String;
38.
procedure To_C (Item : in Wide_String;
Target : out wchar_array;
Count : out size_t;
Append_Nul : in Boolean := True);
39.
procedure To_Ada (Item : in wchar_array;
Target : out Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
40.
Terminator_Error : exception;
41.
end Interfaces.C;
42. Each of the types declared in Interfaces.C is C-compatible.
43. The types int, short, long, unsigned, ptrdiff_t, size_t, double, char,
and wchar_t correspond respectively to the C types having the same names.
The types signed_char, unsigned_short, unsigned_long, unsigned_char,
C_float, and long_double correspond respectively to the C types signed
char, unsigned short, unsigned long, unsigned char, float, and long
double.
44. The type of the subtype plain_char is either signed_char or
unsigned_char, depending on the C implementation.
45.
function To_C (Item : in Character) return char;
function To_Ada (Item : in char ) return Character;
a. The functions To_C and To_Ada map between the Ada type Character and
the C type char.
1.
function Is_Nul_Terminated (Item : in char_array) return Boolean;
a. The result of Is_Nul_Terminated is True if Item contains nul, and is
False otherwise.
1.
function To_C (Item : in String;
Append_Nul : in Boolean := True)
return char_array;
function To_Ada (Item : in char_array;
Trim_Nul : in Boolean := True)
return String;
a. The result of To_C is a char_array value of length Item'Length (if
Append_Nul is False) or Item'Length+1 (if Append_Nul is True). The
lower bound is 0. For each component Item(I), the corresponding
component in the result is To_C applied to Item(I). The value nul is
appended if Append_Nul is True.
b. The result of To_Ada is a String whose length is Item'Length (if
Trim_Nul is False) or the length of the slice of Item preceding the
first nul (if Trim_Nul is True). The lower bound of the result is 1.
If Trim_Nul is False, then for each component Item(I) the
corresponding component in the result is To_Ada applied to Item(I).
If Trim_Nul is True, then for each component Item(I) before the
first nul the corresponding component in the result is To_Ada
applied to Item(I). The function propagates Terminator_Error if
Trim_Nul is True and Item does not contain nul.
1.
procedure To_C (Item : in String;
Target : out char_array;
Count : out size_t;
Append_Nul : in Boolean := True);
procedure To_Ada (Item : in char_array;
Target : out String;
Count : out Natural;
Trim_Nul : in Boolean := True);
a. For procedure To_C, each element of Item is converted (via the To_C
function) to a char, which is assigned to the corresponding element
of Target. If Append_Nul is True, nul is then assigned to the next
element of Target. In either case, Count is set to the number of
Target elements assigned. If Target is not long enough,
Constraint_Error is propagated.
b. For procedure To_Ada, each element of Item (if Trim_Nul is False) or
each element of Item preceding the first nul (if Trim_Nul is True)
is converted (via the To_Ada function) to a Character, which is
assigned to the corresponding element of Target. Count is set to the
number of Target elements assigned. If Target is not long enough,
Constraint_Error is propagated. If Trim_Nul is True and Item does
not contain nul, then Terminator_Error is propagated.
1.
function Is_Nul_Terminated (Item : in wchar_array) return Boolean;
a. The result of Is_Nul_Terminated is True if Item contains wide_nul,
and is False otherwise.
1.
function To_C (Item : in Wide_Character) return wchar_t;
function To_Ada (Item : in wchar_t ) return Wide_Character;
a. To_C and To_Ada provide the mappings between the Ada and C wide
character types.
1.
function To_C (Item : in Wide_String;
Append_Nul : in Boolean := True)
return wchar_array;
function To_Ada (Item : in wchar_array;
Trim_Nul : in Boolean := True)
return Wide_String;
procedure To_C (Item : in Wide_String;
Target : out wchar_array;
Count : out size_t;
Append_Nul : in Boolean := True);
procedure To_Ada (Item : in wchar_array;
Target : out Wide_String;
Count : out Natural;
Trim_Nul : in Boolean := True);
a. The To_C and To_Ada subprograms that convert between Wide_String and
wchar_array have analogous effects to the To_C and To_Ada
subprograms that convert between String and char_array, except that
wide_nul is used instead of nul.
Implementation Requirements
1. An implementation shall support pragma Convention with a C
convention_identifier for a C-eligible type, see B.1.
Implementation Permissions
2. An implementation may provide additional declarations in the C interface
packages.
Implementation Advice
3. An implementation should support the following interface correspondences
between Ada and C.
a. An Ada procedure corresponds to a void-returning C function.
b. An Ada function corresponds to a non-void C function.
c. An Ada in scalar parameter is passed as a scalar argument to a C
function.
d. An Ada in parameter of an access-to-object type with designated type
T is passed as a t* argument to a C function, where t is the C type
corresponding to the Ada type T.
e. An Ada access T parameter, or an Ada out or in out parameter of an
elementary type T, is passed as a t* argument to a C function, where
t is the C type corresponding to the Ada type T. In the case of an
elementary out or in out parameter, a pointer to a temporary copy is
used to preserve by-copy semantics.
f. An Ada parameter of a record type T, of any mode, is passed as a t*
argument to a C function, where t is the C struct corresponding to
the Ada type T.
g. An Ada parameter of an array type with component type T, of any
mode, is passed as a t* argument to a C function, where t is the C
type corresponding to the Ada type T.
h. An Ada parameter of an access-to-subprogram type is passed as a
pointer to a C function whose prototype corresponds to the
designated subprogram's specification.
NOTES
1. (9) Values of type char_array are not implicitly terminated with nul. If
a char_array is to be passed as a parameter to an imported C function
requiring nul termination, it is the programmer's responsibility to
obtain this effect.
2. (10) To obtain the effect of C's sizeof(item_type), where Item_Type is
the corresponding Ada type, evaluate the expression:
size_t(Item_Type'Size/CHAR_BIT).
3. (11) There is no explicit support for C's union types. Unchecked
conversions can be used to obtain the effect of C unions.
4. (12) A C function that takes a variable number of arguments can
correspond to several Ada subprograms, taking various specific numbers
and types of parameters.
Examples
5. Example of using the Interfaces.C package:
6.
--Calling the C Library Function strcpy
with Interfaces.C;
procedure Test is
package C renames Interfaces.C;
use type C.char_array;
-- Call <string.h> strcpy:
-- C definition of strcpy:
-- char *strcpy(char *s1, const char *s2);
-- This function copies the string pointed to by s2
-- (including the terminating null character) into the array
-- pointed to by s1. If copying takes place between objects that
-- overlap, the behavior is undefined. The strcpy function
-- returns the value of s1.
7.
-- Note: since the C function's return value is of no interest,
-- the Ada interface is a procedure
procedure Strcpy (Target : out C.char_array;
Source : in C.char_array);
8.
pragma Import(C, Strcpy, "strcpy");
9.
Chars1 : C.char_array(1┬╖┬╖20);
Chars2 : C.char_array(1┬╖┬╖20);
10.
begin
Chars2(1┬╖┬╖6) := "qwert" & C.nul;
11.
Strcpy(Chars1, Chars2);
12.
-- Now Chars1(1┬╖┬╖6) = "qwert" & C.Nul
13.
end Test;
B.3.1 The Package Interfaces.C.Strings
B.3.2 The Generic Package Interfaces.C.Pointers
ΓòÉΓòÉΓòÉ 18.3.1. The Package Interfaces.C.Strings ΓòÉΓòÉΓòÉ
1. The package Interfaces.C.Strings declares types and subprograms allowing
an Ada program to allocate, reference, update, and free C-style strings.
In particular, the private type chars_ptr corresponds to a common use of
``char *'' in C programs, and an object of this type can be passed to a
subprogram to which pragma Import(C,┬╖┬╖┬╖) has been applied, and for which
``char *'' is the type of the argument of the C function.
Static Semantics
2. The library package Interfaces.C.Strings has the following declaration:
3.
package Interfaces.C.Strings is
pragma Preelaborate(Strings);
4.
type char_array_access is access all char_array;
5.
type chars_ptr is private;
6.
type chars_ptr_array is array (size_t range <>) of chars_ptr;
7.
Null_Ptr : constant chars_ptr;
8.
function To_Chars_Ptr (Item : in char_array_access;
Nul_Check : in Boolean := False)
return chars_ptr;
9.
function New_Char_Array (Chars : in char_array) return chars_ptr;
10.
function New_String (Str : in String) return chars_ptr;
11.
procedure Free (Item : in out chars_ptr);
12.
Dereference_Error : exception;
13.
function Value (Item : in chars_ptr) return char_array;
14.
function Value (Item : in chars_ptr; Length : in size_t)
return char_array;
15.
function Value (Item : in chars_ptr) return String;
16.
function Value (Item : in chars_ptr; Length : in size_t)
return String;
17.
function Strlen (Item : in chars_ptr) return size_t;
18.
procedure Update (Item : in chars_ptr;
Offset : in size_t;
Chars : in char_array;
Check : in Boolean := True);
19.
procedure Update (Item : in chars_ptr;
Offset : in size_t;
Str : in String;
Check : in Boolean := True);
20.
Update_Error : exception;
21.
private
┬╖┬╖┬╖ -- not specified by the language
end Interfaces.C.Strings;
22. The type chars_ptr is C-compatible and corresponds to the use of C's
``char *'' for a pointer to the first char in a char array terminated by
nul. When an object of type chars_ptr is declared, its value is by
default set to Null_Ptr, unless the object is imported, see B.1.
23.
function To_Chars_Ptr (Item : in char_array_access;
Nul_Check : in Boolean := False)
return chars_ptr;
a. If Item is null, then To_Chars_Ptr returns Null_Ptr. Otherwise, if
Nul_Check is True and Item.all does not contain nul, then the
function propagates Terminator_Error; if Nul_Check is True and
Item.all does contain nul, To_Chars_Ptr performs a pointer
conversion with no allocation of memory.
1.
function New_Char_Array (Chars : in char_array) return chars_ptr;
a. This function returns a pointer to an allocated object initialized
to Chars(Chars'First ┬╖┬╖ Index) & nul, where
b. Index = Chars'Last if Chars does not contain nul, or
c. Index is the smallest size_t value I such that Chars(I+1) = nul.
Storage_Error is propagated if the allocation fails.
1.
function New_String (Str : in String) return chars_ptr;
a. This function is equivalent to New_Char_Array(To_C(Str)).
1.
procedure Free (Item : in out chars_ptr);
a. If Item is Null_Ptr, then Free has no effect. Otherwise, Free
releases the storage occupied by Value(Item), and resets Item to
Null_Ptr.
1.
function Value (Item : in chars_ptr) return char_array;
a. If Item = Null_Ptr then Value propagates Dereference_Error.
Otherwise Value returns the prefix of the array of chars pointed to
by Item, up to and including the first nul. The lower bound of the
result is 0. If Item does not point to a nul-terminated string, then
execution of Value is erroneous.
1.
function Value (Item : in chars_ptr; Length : in size_t)
return char_array;
a. If Item = Null_Ptr then Value(Item) propagates Dereference_Error.
Otherwise Value returns the shorter of two arrays: the first Length
chars pointed to by Item, and Value(Item). The lower bound of the
result is 0.
1.
function Value (Item : in chars_ptr) return String;
a. Equivalent to To_Ada(Value(Item), Trim_Nul=>True).
1.
function Value (Item : in chars_ptr; Length : in size_t)
return String;
a. Equivalent to To_Ada(Value(Item, Length), Trim_Nul=>True).
1.
function Strlen (Item : in chars_ptr) return size_t;
a. Returns Val'Length-1 where Val = Value(Item); propagates
Dereference_Error if Item = Null_Ptr.
1.
procedure Update (Item : in chars_ptr;
Offset : in size_t;
Chars : in char_array;
Check : Boolean := True);
a. This procedure updates the value pointed to by Item, starting at
position Offset, using Chars as the data to be copied into the
array. Overwriting the nul terminator, and skipping with the Offset
past the nul terminator, are both prevented if Check is True, as
follows:
1. Let N = Strlen(Item). If Check is True, then:
a. If Offset+Chars'Length>N, propagate Update_Error.
b. Otherwise, overwrite the data in the array pointed to by
Item, starting at the char at position Offset, with the
data in Chars.
1. If Check is False, then processing is as above, but with no
check that Offset+Chars'Length>N.
1.
procedure Update (Item : in chars_ptr;
Offset : in size_t;
Str : in String;
Check : in Boolean := True);
a. Equivalent to Update(Item, Offset, To_C(Str), Check).
Erroneous Execution
1. Execution of any of the following is erroneous if the Item parameter is
not null_ptr and Item does not point to a nul-terminated array of chars.
a. a Value function not taking a Length parameter,
b. the Free procedure,
c. the Strlen function.
1. Execution of Free(X) is also erroneous if the chars_ptr X was not
returned by New_Char_Array or New_String.
2. Reading or updating a freed char_array is erroneous.
3. Execution of Update is erroneous if Check is False and a call with Check
equal to True would have propagated Update_Error.
NOTES
4. (13) New_Char_Array and New_String might be implemented either through
the allocation function from the C environment (``malloc'') or through
Ada dynamic memory allocation (``new''). The key points are
a. the returned value (a chars_ptr) is represented as a C ``char *'' so
that it may be passed to C functions;
b. the allocated object should be freed by the programmer via a call of
Free, not by a called C function.
ΓòÉΓòÉΓòÉ 18.3.2. The Generic Package Interfaces.C.Pointers ΓòÉΓòÉΓòÉ
1. The generic package Interfaces.C.Pointers allows the Ada programmer to
perform C-style operations on pointers. It includes an access type
Pointer, Value functions that dereference a Pointer and deliver the
designated array, several pointer arithmetic operations, and ``copy''
procedures that copy the contents of a source pointer into the array
designated by a destination pointer. As in C, it treats an object Ptr of
type Pointer as a pointer to the first element of an array, so that for
example, adding 1 to Ptr yields a pointer to the second element of the
array.
2. The generic allows two styles of usage: one in which the array is
terminated by a special terminator element; and another in which the
programmer needs to keep track of the length.
Static Semantics
3. The generic library package Interfaces.C.Pointers has the following
declaration:
4.
generic
type Index is (<>);
type Element is private;
type Element_Array is array (Index range <>) of aliased Element;
Default_Terminator : Element;
package Interfaces.C.Pointers is
pragma Preelaborate(Pointers);
5.
type Pointer is access all Element;
6.
function Value(Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return Element_Array;
7.
function Value(Ref : in Pointer;
Length : in ptrdiff_t)
return Element_Array;
8.
Pointer_Error : exception;
9.
-- C-style Pointer arithmetic
10.
function "+" (Left : in Pointer;
Right : in ptrdiff_t) return Pointer;
function "+" (Left : in ptrdiff_t;
Right : in Pointer) return Pointer;
function "-" (Left : in Pointer;
Right : in ptrdiff_t) return Pointer;
function "-" (Left : in Pointer;
Right : in Pointer) return ptrdiff_t;
11.
procedure Increment (Ref : in out Pointer);
procedure Decrement (Ref : in out Pointer);
12.
pragma Convention (Intrinsic, "+");
pragma Convention (Intrinsic, "-");
pragma Convention (Intrinsic, Increment);
pragma Convention (Intrinsic, Decrement);
13.
function Virtual_Length
(Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return ptrdiff_t;
14.
procedure Copy_Terminated_Array
(Source : in Pointer;
Target : in Pointer;
Limit : in ptrdiff_t := ptrdiff_t'Last;
Terminator : in Element := Default_Terminator);
15.
procedure Copy_Array (Source : in Pointer;
Target : in Pointer;
Length : in ptrdiff_t);
16.
end Interfaces.C.Pointers;
17. The type Pointer is C-compatible and corresponds to one use of C's
``Element *''. An object of type Pointer is interpreted as a pointer to
the initial Element in an Element_Array. Two styles are supported:
a. Explicit termination of an array value with Default_Terminator (a
special terminator value);
b. Programmer-managed length, with Default_Terminator treated simply as
a data element.
1.
function Value(Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return Element_Array;
a. This function returns an Element_Array whose value is the array
pointed to by Ref, up to and including the first Terminator; the
lower bound of the array is Index'First.
Interfaces.C.Strings.Dereference_Error is propagated if Ref is null.
1.
function Value(Ref : in Pointer;
Length : in ptrdiff_t)
return Element_Array;
a. This function returns an Element_Array comprising the first Length
elements pointed to by Ref. The exception
Interfaces.C.Strings.Dereference_Error is propagated if Ref is null.
1. The "+" and "-" functions perform arithmetic on Pointer values, based on
the Size of the array elements. In each of these functions, Pointer_Error
is propagated if a Pointer parameter is null.
2.
procedure Increment (Ref : in out Pointer);
a. Equivalent to Ref := Ref+1.
1.
procedure Decrement (Ref : in out Pointer);
a. Equivalent to Ref := Ref-1.
1.
function Virtual_Length
(Ref : in Pointer;
Terminator : in Element := Default_Terminator)
return ptrdiff_t;
a. Returns the number of Elements, up to the one just before the first
Terminator, in Value(Ref, Terminator).
1.
procedure Copy_Terminated_Array
(Source : in Pointer;
Target : in Pointer;
Limit : in ptrdiff_t := ptrdiff_t'Last;
Terminator : in Element := Default_Terminator);
a. This procedure copies Value(Source, Terminator) into the array
pointed to by Target; it stops either after Terminator has been
copied, or the number of elements copied is Limit, whichever occurs
first. Dereference_Error is propagated if either Source or Target is
null.
1.
procedure Copy_Array (Source : in Pointer;
Target : in Pointer;
Length : in ptrdiff_t);
a. This procedure copies the first Length elements from the array
pointed to by Source, into the array pointed to by Target.
Dereference_Error is propagated if either Source or Target is null.
Erroneous Execution
1. It is erroneous to dereference a Pointer that does not designate an
aliased Element.
2. Execution of Value(Ref, Terminator) is erroneous if Ref does not
designate an aliased Element in an Element_Array terminated by
Terminator.
3. Execution of Value(Ref, Length) is erroneous if Ref does not designate an
aliased Element in an Element_Array containing at least Length Elements
between the designated Element and the end of the array, inclusive.
4. Execution of Virtual_Length(Ref, Terminator) is erroneous if Ref does not
designate an aliased Element in an Element_Array terminated by
Terminator.
5. Execution of Copy_Terminated_Array(Source, Target, Limit, Terminator) is
erroneous in either of the following situations:
a. Execution of both Value(Source,Terminator) and Value(Source,Limit)
are erroneous, or
b. Copying writes past the end of the array containing the Element
designated by Target.
1. Execution of Copy_Array(Source, Target, Length) is erroneous if either
Value(Source, Length) is erroneous, or copying writes past the end of the
array containing the Element designated by Target.
NOTES
2. (14) To compose a Pointer from an Element_Array, use 'Access on the first
element. For example (assuming appropriate instantiations):
3.
Some_Array : Element_Array(0┬╖┬╖5) ;
Some_Pointer : Pointer := Some_Array(0)'Access;
Examples
4. Example of Interfaces.C.Pointers:
5.
with Interfaces.C.Pointers;
with Interfaces.C.Strings;
procedure Test_Pointers is
package C renames Interfaces.C;
package Char_Ptrs is
new C.Pointers (Index => C.size_t,
Element => C.char,
Element_Array => C.char_array,
Default_Terminator => C.nul);
6.
use type Char_Ptrs.Pointer;
subtype Char_Star is Char_Ptrs.Pointer;
7.
procedure Strcpy (Target_Ptr, Source_Ptr : Char_Star) is
Target_Temp_Ptr : Char_Star := Target_Ptr;
Source_Temp_Ptr : Char_Star := Source_Ptr;
Element : C.char;
begin
if Target_Temp_Ptr = null or Source_Temp_Ptr = null then
raise C.Strings.Dereference_Error;
end if;
8.
loop
Element := Source_Temp_Ptr.all;
Target_Temp_Ptr.all := Element;
exit when Element = C.nul;
Char_Ptrs.Increment(Target_Temp_Ptr);
Char_Ptrs.Increment(Source_Temp_Ptr);
end loop;
end Strcpy;
begin
┬╖┬╖┬╖
end Test_Pointers;
ΓòÉΓòÉΓòÉ 18.4. Interfacing with COBOL ΓòÉΓòÉΓòÉ
1. The facilities relevant to interfacing with the COBOL language are the
package Interfaces.COBOL and support for the Import, Export and
Convention pragmas with convention_identifier COBOL.
2. The COBOL interface package supplies several sets of facilities:
a. A set of types corresponding to the native COBOL types of the
supported COBOL implementation (so-called ``internal COBOL
representations''), allowing Ada data to be passed as parameters to
COBOL programs
b. A set of types and constants reflecting external data
representations such as might be found in files or databases,
allowing COBOL-generated data to be read by an Ada program, and
Ada-generated data to be read by COBOL programs
c. A generic package for converting between an Ada decimal type value
and either an internal or external COBOL representation
Static Semantics
1. The library package Interfaces.COBOL has the following declaration:
2.
package Interfaces.COBOL is
pragma Preelaborate(COBOL);
3.
-- Types and operations for internal data representations
4.
type Floating is digits implementation-defined;
type Long_Floating is digits implementation-defined;
5.
type Binary is range implementation-defined;
type Long_Binary is range implementation-defined;
6.
Max_Digits_Binary : constant := implementation-defined;
Max_Digits_Long_Binary : constant := implementation-defined;
7.
type Decimal_Element is mod implementation-defined;
type Packed_Decimal is
array (Positive range <>) of Decimal_Element;
pragma Pack(Packed_Decimal);
8.
type COBOL_Character is implementation-defined character type;
9.
Ada_To_COBOL : array (Character) of COBOL_Character
:= implementation-defined;
10.
COBOL_To_Ada : array (COBOL_Character) of Character
:= implementation-defined;
11.
type Alphanumeric is
array (Positive range <>) of COBOL_Character;
pragma Pack(Alphanumeric);
12.
function To_COBOL (Item : in String) return Alphanumeric;
function To_Ada (Item : in Alphanumeric) return String;
13.
procedure To_COBOL (Item : in String;
Target : out Alphanumeric;
Last : out Natural);
14.
procedure To_Ada (Item : in Alphanumeric;
Target : out String;
Last : out Natural);
15.
type Numeric is array (Positive range <>) of COBOL_Character;
pragma Pack(Numeric);
16.
-- Formats for COBOL data representations
17.
type Display_Format is private;
18.
Unsigned : constant Display_Format;
Leading_Separate : constant Display_Format;
Trailing_Separate : constant Display_Format;
Leading_Nonseparate : constant Display_Format;
Trailing_Nonseparate : constant Display_Format;
19.
type Binary_Format is private;
20.
High_Order_First : constant Binary_Format;
Low_Order_First : constant Binary_Format;
Native_Binary : constant Binary_Format;
21.
type Packed_Format is private;
22.
Packed_Unsigned : constant Packed_Format;
Packed_Signed : constant Packed_Format;
23.
-- Types for external representation of COBOL binary data
24.
type Byte is mod 2**COBOL_Character'Size;
type Byte_Array is array (Positive range <>) of Byte;
pragma Pack (Byte_Array);
25.
Conversion_Error : exception;
26.
generic
type Num is delta <> digits <>;
package Decimal_Conversions is
27.
-- Display Formats: data values are represented as Numeric
28.
function Valid (Item : in Numeric;
Format : in Display_Format) return Boolean;
29.
function Length (Format : in Display_Format) return Natural;
30.
function To_Decimal (Item : in Numeric;
Format : in Display_Format) return Num;
31.
function To_Display (Item : in Num;
Format : in Display_Format)
return Numeric;
32.
-- Packed Formats:
-- data values are represented as Packed_Decimal
33.
function Valid (Item : in Packed_Decimal;
Format : in Packed_Format) return Boolean;
34.
function Length (Format : in Packed_Format) return Natural;
35.
function To_Decimal (Item : in Packed_Decimal;
Format : in Packed_Format) return Num;
36.
function To_Packed (Item : in Num;
Format : in Packed_Format)
return Packed_Decimal;
37.
-- Binary Formats:
-- external data values are represented as Byte_Array
38.
function Valid (Item : in Byte_Array;
Format : in Binary_Format) return Boolean;
39.
function Length (Format : in Binary_Format) return Natural;
function To_Decimal (Item : in Byte_Array;
Format : in Binary_Format) return Num;
40.
function To_Binary (Item : in Num;
Format : in Binary_Format)
return Byte_Array;
41.
-- Internal Binary formats:
-- data values are of type Binary or Long_Binary
42.
function To_Decimal (Item : in Binary) return Num;
function To_Decimal (Item : in Long_Binary) return Num;
43.
function To_Binary (Item : in Num) return Binary;
function To_Long_Binary (Item : in Num) return Long_Binary;
44.
end Decimal_Conversions;
45.
private
┬╖┬╖┬╖ -- not specified by the language
end Interfaces.COBOL;
46. Each of the types in Interfaces.COBOL is COBOL-compatible.
47. The types Floating and Long_Floating correspond to the native types in
COBOL for data items with computational usage implemented by floating
point. The types Binary and Long_Binary correspond to the native types in
COBOL for data items with binary usage, or with computational usage
implemented by binary.
48. Max_Digits_Binary is the largest number of decimal digits in a numeric
value that is represented as Binary. Max_Digits_Long_Binary is the
largest number of decimal digits in a numeric value that is represented
as Long_Binary.
49. The type Packed_Decimal corresponds to COBOL's packed-decimal usage.
50. The type COBOL_Character defines the run-time character set used in the
COBOL implementation. Ada_To_COBOL and COBOL_To_Ada are the mappings
between the Ada and COBOL run-time character sets.
51. Type Alphanumeric corresponds to COBOL's alphanumeric data category.
52. Each of the functions To_COBOL and To_Ada converts its parameter based on
the mappings Ada_To_COBOL and COBOL_To_Ada, respectively. The length of
the result for each is the length of the parameter, and the lower bound
of the result is 1. Each component of the result is obtained by applying
the relevant mapping to the corresponding component of the parameter.
53. Each of the procedures To_COBOL and To_Ada copies converted elements from
Item to Target, using the appropriate mapping (Ada_To_COBOL or
COBOL_To_Ada, respectively). The index in Target of the last element
assigned is returned in Last (0 if Item is a null array). If Item'Length
exceeds Target'Length, Constraint_Error is propagated.
54. Type Numeric corresponds to COBOL's numeric data category with display
usage.
55. The types Display_Format, Binary_Format, and Packed_Format are used in
conversions between Ada decimal type values and COBOL internal or
external data representations. The value of the constant Native_Binary is
either High_Order_First or Low_Order_First, depending on the
implementation.
56.
function Valid (Item : in Numeric;
Format : in Display_Format) return Boolean;
a. The function Valid checks that the Item parameter has a value
consistent with the value of Format. If the value of Format is other
than Unsigned, Leading_Separate, and Trailing_Separate, the effect
is implementation defined. If Format does have one of these values,
the following rules apply:
1. Format=Unsigned: if Item comprises zero or more leading space
characters followed by one or more decimal digit characters
then Valid returns True, else it returns False.
2. Format=Leading_Separate: if Item comprises zero or more leading
space characters, followed by a single occurrence of the plus
or minus sign character, and then one or more decimal digit
characters, then Valid returns True, else it returns False.
3. Format=Trailing_Separate: if Item comprises zero or more
leading space characters, followed by one or more decimal digit
characters and finally a plus or minus sign character, then
Valid returns True, else it returns False.
1.
function Length (Format : in Display_Format) return Natural;
a. The Length function returns the minimal length of a Numeric value
sufficient to hold any value of type Num when represented as Format.
1.
function To_Decimal (Item : in Numeric;
Format : in Display_Format) return Num;
a. Produces a value of type Num corresponding to Item as represented by
Format. The number of digits after the assumed radix point in Item
is Num'Scale. Conversion_Error is propagated if the value
represented by Item is outside the range of Num.
1.
function To_Display (Item : in Num;
Format : in Display_Format) return Numeric;
a. This function returns the Numeric value for Item, represented in
accordance with Format. Conversion_Error is propagated if Num is
negative and Format is Unsigned.
1.
function Valid (Item : in Packed_Decimal;
Format : in Packed_Format) return Boolean;
a. This function returns True if Item has a value consistent with
Format, and False otherwise. The rules for the formation of
Packed_Decimal values are implementation defined.
1.
function Length (Format : in Packed_Format) return Natural;
a. This function returns the minimal length of a Packed_Decimal value
sufficient to hold any value of type Num when represented as Format.
1.
function To_Decimal (Item : in Packed_Decimal;
Format : in Packed_Format) return Num;
a. Produces a value of type Num corresponding to Item as represented by
Format. Num'Scale is the number of digits after the assumed radix
point in Item. Conversion_Error is propagated if the value
represented by Item is outside the range of Num.
1.
function To_Packed (Item : in Num;
Format : in Packed_Format)
return Packed_Decimal;
a. This function returns the Packed_Decimal value for Item, represented
in accordance with Format. Conversion_Error is propagated if Num is
negative and Format is Packed_Unsigned.
1.
function Valid (Item : in Byte_Array;
Format : in Binary_Format) return Boolean;
a. This function returns True if Item has a value consistent with
Format, and False otherwise.
1.
function Length (Format : in Binary_Format) return Natural;
a. This function returns the minimal length of a Byte_Array value
sufficient to hold any value of type Num when represented as Format.
1.
function To_Decimal (Item : in Byte_Array;
Format : in Binary_Format) return Num;
a. Produces a value of type Num corresponding to Item as represented by
Format. Num'Scale is the number of digits after the assumed radix
point in Item. Conversion_Error is propagated if the value
represented by Item is outside the range of Num.
1.
function To_Binary (Item : in Num;
Format : in Binary_Format) return Byte_Array;
a. This function returns the Byte_Array value for Item, represented in
accordance with Format.
1.
function To_Decimal (Item : in Binary) return Num;
function To_Decimal (Item : in Long_Binary) return Num;
a. These functions convert from COBOL binary format to a corresponding
value of the decimal type Num. Conversion_Error is propagated if
Item is too large for Num.
1.
function To_Binary (Item : in Num) return Binary;
function To_Long_Binary (Item : in Num) return Long_Binary;
a. These functions convert from Ada decimal to COBOL binary format.
Conversion_Error is propagated if the value of Item is too large to
be represented in the result type.
Implementation Requirements
1. An implementation shall support pragma Convention with a COBOL
convention_identifier for a COBOL-eligible type, see B.1.
Implementation Permissions
2. An implementation may provide additional constants of the private types
Display_Format, Binary_Format, or Packed_Format.
3. An implementation may provide further floating point and integer types in
Interfaces.COBOL to match additional native COBOL types, and may also
supply corresponding conversion functions in the generic package
Decimal_Conversions.
Implementation Advice
4. An Ada implementation should support the following interface
correspondences between Ada and COBOL.
a. An Ada access T parameter is passed as a ``BY REFERENCE'' data item
of the COBOL type corresponding to T.
b. An Ada in scalar parameter is passed as a ``BY CONTENT'' data item
of the corresponding COBOL type.
c. Any other Ada parameter is passed as a ``BY REFERENCE'' data item of
the COBOL type corresponding to the Ada parameter type; for scalars,
a local copy is used if necessary to ensure by-copy semantics.
NOTES
1. (15) An implementation is not required to support pragma Convention for
access types, nor is it required to support pragma Import, Export or
Convention for functions.
2. (16) If an Ada subprogram is exported to COBOL, then a call from COBOL
call may specify either ``BY CONTENT'' or ``BY REFERENCE''.
Examples
3. Examples of Interfaces.COBOL:
4.
with Interfaces.COBOL;
procedure Test_Call is
5.
-- Calling a foreign COBOL program
-- Assume that a COBOL program PROG has the following declaration
-- in its LINKAGE section:
-- 01 Parameter-Area
-- 05 NAME PIC X(20).
-- 05 SSN PIC X(9).
-- 05 SALARY PIC 99999V99 USAGE COMP.
-- The effect of PROG is to update SALARY based on some algorithm
6.
package COBOL renames Interfaces.COBOL;
7.
type Salary_Type is delta 0.01 digits 7;
8.
type COBOL_Record is
record
Name : COBOL.Numeric(1┬╖┬╖20);
SSN : COBOL.Numeric(1┬╖┬╖9);
Salary : COBOL.Binary; -- Assume Binary = 32 bits
end record;
pragma Convention (COBOL, COBOL_Record);
9.
procedure Prog (Item : in out COBOL_Record);
pragma Import (COBOL, Prog, "PROG");
10.
package Salary_Conversions is
new COBOL.Decimal_Conversions(Salary_Type);
11.
Some_Salary : Salary_Type := 12_345.67;
Some_Record : COBOL_Record :=
(Name => "Johnson, John ",
SSN => "111223333",
Salary => Salary_Conversions.To_Binary(Some_Salary));
12.
begin
Prog (Some_Record);
┬╖┬╖┬╖
end Test_Call;
13.
with Interfaces.COBOL;
with COBOL_Sequential_IO;
-- Assumed to be supplied by implementation
procedure Test_External_Formats is
14.
-- Using data created by a COBOL program
-- Assume that a COBOL program has created a sequential file with
-- the following record structure, and that we need to
-- process the records in an Ada program
-- 01 EMPLOYEE-RECORD
-- 05 NAME PIC X(20).
-- 05 SSN PIC X(9).
-- 05 SALARY PIC 99999V99 USAGE COMP.
-- 05 ADJUST PIC S999V999 SIGN LEADING SEPARATE.
-- The COMP data is binary (32 bits), high-order byte first
15.
package COBOL renames Interfaces.COBOL;
16.
type Salary_Type is delta 0.01 digits 7;
type Adjustments_Type is delta 0.001 digits 6;
17.
type COBOL_Employee_Record_Type is -- External representation
record
Name : COBOL.Alphanumeric(1┬╖┬╖20);
SSN : COBOL.Alphanumeric(1┬╖┬╖9);
Salary : COBOL.Byte_Array(1┬╖┬╖4);
Adjust : COBOL.Numeric(1┬╖┬╖7); -- Sign and 6 digits
end record;
pragma Convention (COBOL, COBOL_Employee_Record_Type);
18.
package COBOL_Employee_IO is
new COBOL_Sequential_IO(COBOL_Employee_Record_Type);
use COBOL_Employee_IO;
19.
COBOL_File : File_Type;
20.
type Ada_Employee_Record_Type is -- Internal representation
record
Name : String(1┬╖┬╖20);
SSN : String(1┬╖┬╖9);
Salary : Salary_Type;
Adjust : Adjustments_Type;
end record;
21.
COBOL_Record : COBOL_Employee_Record_Type;
Ada_Record : Ada_Employee_Record_Type;
22.
package Salary_Conversions is
new COBOL.Decimal_Conversions(Salary_Type);
use Salary_Conversions;
23.
package Adjustments_Conversions is
new COBOL.Decimal_Conversions(Adjustments_Type);
use Adjustments_Conversions;
24.
begin
Open (COBOL_File, Name => "Some_File");
25.
loop
Read (COBOL_File, COBOL_Record);
26.
Ada_Record.Name := To_Ada(COBOL_Record.Name);
Ada_Record.SSN := To_Ada(COBOL_Record.SSN);
Ada_Record.Salary :=
To_Decimal(COBOL_Record.Salary, COBOL.High_Order_First);
Ada_Record.Adjust :=
To_Decimal(COBOL_Record.Adjust, COBOL.Leading_Separate);
┬╖┬╖┬╖ -- Process Ada_Record
end loop;
exception
when End_Error => ┬╖┬╖┬╖
end Test_External_Formats;
ΓòÉΓòÉΓòÉ 18.5. Interfacing with Fortran ΓòÉΓòÉΓòÉ
1. The facilities relevant to interfacing with the Fortran language are the
package Interfaces.Fortran and support for the Import, Export and
Convention pragmas with convention_identifier Fortran.
2. The package Interfaces.Fortran defines Ada types whose representations
are identical to the default representations of the Fortran intrinsic
types Integer, Real, Double Precision, Complex, Logical, and Character in
a supported Fortran implementation. These Ada types can therefore be used
to pass objects between Ada and Fortran programs.
Static Semantics
3. The library package Interfaces.Fortran has the following declaration:
4.
with Ada.Numerics.Generic_Complex_Types; -- see G.1.1.
pragma Elaborate_All(Ada.Numerics.Generic_Complex_Types);
package Interfaces.Fortran is
pragma Pure(Fortran);
5.
type Fortran_Integer is range implementation-defined;
6.
type Real is digits implementation-defined;
type Double_Precision is digits implementation-defined;
7.
type Logical is new Boolean;
8.
package Single_Precision_Complex_Types is
new Ada.Numerics.Generic_Complex_Types (Real);
9.
type Complex is new Single_Precision_Complex_Types.Complex;
10.
subtype Imaginary is Single_Precision_Complex_Types.Imaginary;
i : Imaginary renames Single_Precision_Complex_Types.i;
j : Imaginary renames Single_Precision_Complex_Types.j;
11.
type Character_Set is implementation-defined character type;
12.
type Fortran_Character is
array (Positive range <>) of Character_Set;
pragma Pack (Fortran_Character);
13.
function To_Fortran (Item : in Character) return Character_Set;
function To_Ada (Item : in Character_Set) return Character;
14.
function To_Fortran (Item : in String) return Fortran_Character;
function To_Ada (Item : in Fortran_Character) return String;
15.
procedure To_Fortran (Item : in String;
Target : out Fortran_Character;
Last : out Natural);
16.
procedure To_Ada (Item : in Fortran_Character;
Target : out String;
Last : out Natural);
17.
end Interfaces.Fortran;
18. The types Fortran_Integer, Real, Double_Precision, Logical, Complex, and
Fortran_Character are Fortran-compatible.
19. The To_Fortran and To_Ada functions map between the Ada type Character
and the Fortran type Character_Set, and also between the Ada type String
and the Fortran type Fortran_Character. The To_Fortran and To_Ada
procedures have analogous effects to the string conversion subprograms
found in Interfaces.COBOL.
Implementation Requirements
20. An implementation shall support pragma Convention with a Fortran
convention_identifier for a Fortran-eligible type, see B.1.
Implementation Permissions
21. An implementation may add additional declarations to the Fortran
interface packages. For example, the Fortran interface package for an
implementation of Fortran 77 (ANSI X3.9-1978) that defines types like
Integer*n, Real*n, Logical*n, and Complex*n may contain the declarations
of types named Integer_Star_n, Real_Star_n, Logical_Star_n, and
Complex_Star_n. (This convention should not apply to Character*n, for
which the Ada analog is the constrained array subtype Fortran_Character
(1┬╖┬╖n).) Similarly, the Fortran interface package for an implementation
of Fortran 90 that provides multiple kinds of intrinsic types, e.g.
Integer (Kind=n), Real (Kind=n), Logical (Kind=n), Complex (Kind=n), and
Character (Kind=n), may contain the declarations of types with the
recommended names Integer_Kind_n, Real_Kind_n, Logical_Kind_n,
Complex_Kind_n, and Character_Kind_n.
Implementation Advice
22. An Ada implementation should support the following interface
correspondences between Ada and Fortran:
a. An Ada procedure corresponds to a Fortran subroutine.
b. An Ada function corresponds to a Fortran function.
c. An Ada parameter of an elementary, array, or record type T is passed
as a T(F) argument to a Fortran procedure, where T(F) is the Fortran
type corresponding to the Ada type T, and where the INTENT attribute
of the corresponding dummy argument matches the Ada formal parameter
mode; the Fortran implementation's parameter passing conventions are
used. For elementary types, a local copy is used if necessary to
ensure by-copy semantics.
d. An Ada parameter of an access-to-subprogram type is passed as a
reference to a Fortran procedure whose interface corresponds to the
designated subprogram's specification.
NOTES
1. (17) An object of a Fortran-compatible record type, declared in a library
package or subprogram, can correspond to a Fortran common block; the type
also corresponds to a Fortran ``derived type''.
Examples
2. Example of Interfaces.Fortran:
3.
with Interfaces.Fortran;
use Interfaces.Fortran;
procedure Ada_Application is
4.
type Fortran_Matrix is array
(Integer range <>,
Integer range <>) of Double_Precision;
pragma Convention (Fortran, Fortran_Matrix);
-- stored in Fortran's column-major order
procedure Invert
(Rank : in Fortran_Integer;
X : in out Fortran_Matrix);
pragma Import (Fortran, Invert);
-- a Fortran subroutine
5.
Rank : constant Fortran_Integer := 100;
My_Matrix : Fortran_Matrix (1 ┬╖┬╖ Rank, 1 ┬╖┬╖ Rank);
6.
begin
7.
┬╖┬╖┬╖
My_Matrix := ┬╖┬╖┬╖;
┬╖┬╖┬╖
Invert (Rank, My_Matrix);
┬╖┬╖┬╖
8.
end Ada_Application;
ΓòÉΓòÉΓòÉ 19. Systems Programming (normative) ΓòÉΓòÉΓòÉ
1. The Systems Programming Annex specifies additional capabilities provided
for low-level programming. These capabilities are also required in many
real-time, embedded, distributed, and information systems.
C.1 Access to Machine Operations
C.2 Required Representation Support
C.3 Interrupt Support
C.4 Preelaboration Requirements
C.5 Pragma Discard_Names
C.6 Shared Variable Control
C.7 Task Identification and Attributes --- The
Detailed Node Listing ---
C.1 Access to Machine Operations
C.2 Required Representation Support
C.3 Interrupt Support
C.3.1 Protected Procedure Handlers
C.3.2 The Package Interrupts
C.4 Preelaboration Requirements
C.5 Pragma Discard_Names
C.6 Shared Variable Control
C.7 Task Identification and Attributes
C.7.1 The Package Task_Identification
C.7.2 The Package Task_Attributes
ΓòÉΓòÉΓòÉ 19.1. Access to Machine Operations ΓòÉΓòÉΓòÉ
1. This clause specifies rules regarding access to machine instructions from
within an Ada program.
Implementation Requirements
2. The implementation shall support machine code insertions, see 13.8, or
intrinsic subprograms, see 6.3.1, (or both). Implementation-defined
attributes shall be provided to allow the use of Ada entities as
operands.
Implementation Advice
3. The machine code or intrinsics support should allow access to all
operations normally available to assembly language programmers for the
target environment, including privileged instructions, if any.
4. The interfacing pragmas (see B) should support interface to assembler;
the default assembler should be associated with the convention identifier
Assembler.
5. If an entity is exported to assembly language, then the implementation
should allocate it at an addressable location, and should ensure that it
is retained by the linking process, even if not otherwise referenced from
the Ada code. The implementation should assume that any call to a machine
code or assembler subprogram is allowed to read or update every object
that is specified as exported.
Documentation Requirements
6. The implementation shall document the overhead associated with calling
machine-code or intrinsic subprograms, as compared to a fully-inlined
call, and to a regular out-of-line call.
7. The implementation shall document the types of the package
System.Machine_Code usable for machine code insertions, and the
attributes to be used in machine code insertions for references to Ada
entities.
8. The implementation shall document the subprogram calling conventions
associated with the convention identifiers available for use with the
interfacing pragmas (Ada and Assembler, at a minimum), including register
saving, exception propagation, parameter passing, and function value
returning.
9. For exported and imported subprograms, the implementation shall document
the mapping between the Link_Name string, if specified, or the Ada
designator, if not, and the external link name used for such a
subprogram.
Implementation Advice
10. The implementation should ensure that little or no overhead is associated
with calling intrinsic and machine-code subprograms.
11. It is recommended that intrinsic subprograms be provided for convenient
access to any machine operations that provide special capabilities or
efficiency and that are not otherwise available through the language
constructs. Examples of such instructions include:
a. Atomic read-modify-write operations -- e.g., test and set, compare
and swap, decrement and test, enqueue/dequeue.
b. Standard numeric functions -- e.g., sin, log.
c. String manipulation operations -- e.g., translate and test.
d. Vector operations -- e.g., compare vector against thresholds.
e. Direct operations on I/O ports.
ΓòÉΓòÉΓòÉ 19.2. Required Representation Support ΓòÉΓòÉΓòÉ
1. This clause specifies minimal requirements on the implementation's
support for representation items and related features.
Implementation Requirements
2. The implementation shall support at least the functionality defined by
the recommended levels of support in 13.
ΓòÉΓòÉΓòÉ 19.3. Interrupt Support ΓòÉΓòÉΓòÉ
1. This clause specifies the language-defined model for hardware interrupts
in addition to mechanisms for handling interrupts.
Dynamic Semantics
2. An interrupt represents a class of events that are detected by the
hardware or the system software. Interrupts are said to occur. An
occurrence of an interrupt is separable into generation and delivery.
Generation of an interrupt is the event in the underlying hardware or
system that makes the interrupt available to the program. Delivery is the
action that invokes part of the program as response to the interrupt
occurrence. Between generation and delivery, the interrupt occurrence (or
interrupt) is pending. Some or all interrupts may be blocked. When an
interrupt is blocked, all occurrences of that interrupt are prevented
from being delivered. Certain interrupts are reserved. The set of
reserved interrupts is implementation defined. A reserved interrupt is
either an interrupt for which user-defined handlers are not supported, or
one which already has an attached handler by some other
implementation-defined means. Program units can be connected to
non-reserved interrupts. While connected, the program unit is said to be
attached to that interrupt. The execution of that program unit, the
interrupt handler, is invoked upon delivery of the interrupt occurrence.
3. While a handler is attached to an interrupt, it is called once for each
delivered occurrence of that interrupt. While the handler executes, the
corresponding interrupt is blocked.
4. While an interrupt is blocked, all occurrences of that interrupt are
prevented from being delivered. Whether such occurrences remain pending
or are lost is implementation defined.
5. Each interrupt has a default treatment which determines the system's
response to an occurrence of that interrupt when no user-defined handler
is attached. The set of possible default treatments is implementation
defined, as is the method (if one exists) for configuring the default
treatments for interrupts.
6. An interrupt is delivered to the handler (or default treatment) that is
in effect for that interrupt at the time of delivery.
7. An exception propagated from a handler that is invoked by an interrupt
has no effect.
8. If the Ceiling_Locking policy, see D.3, is in effect, the interrupt
handler executes with the active priority that is the ceiling priority of
the corresponding protected object.
Implementation Requirements
9. The implementation shall provide a mechanism to determine the minimum
stack space that is needed for each interrupt handler and to reserve that
space for the execution of the handler. This space should accommodate
nested invocations of the handler where the system permits this.
10. If the hardware or the underlying system holds pending interrupt
occurrences, the implementation shall provide for later delivery of these
occurrences to the program.
11. If the Ceiling_Locking policy is not in effect, the implementation shall
provide means for the application to specify whether interrupts are to be
blocked during protected actions.
Documentation Requirements
12. The implementation shall document the following items:
a. For each interrupt, which interrupts are blocked from delivery when
a handler attached to that interrupt executes (either as a result of
an interrupt delivery or of an ordinary call on a procedure of the
corresponding protected object).
b. Any interrupts that cannot be blocked, and the effect of attaching
handlers to such interrupts, if this is permitted.
c. Which run-time stack an interrupt handler uses when it executes as a
result of an interrupt delivery; if this is configurable, what is
the mechanism to do so; how to specify how much space to reserve on
that stack.
d. Any implementation- or hardware-specific activity that happens
before a user-defined interrupt handler gets control (e.g., reading
device registers, acknowledging devices).
e. Any timing or other limitations imposed on the execution of
interrupt handlers.
f. The state (blocked/unblocked) of the non-reserved interrupts when
the program starts; if some interrupts are unblocked, what is the
mechanism a program can use to protect itself before it can attach
the corresponding handlers.
g. Whether the interrupted task is allowed to resume execution before
the interrupt handler returns.
h. The treatment of interrupt occurrences that are generated while the
interrupt is blocked; i.e., whether one or more occurrences are held
for later delivery, or all are lost.
i. Whether predefined or implementation-defined exceptions are raised
as a result of the occurrence of any interrupt, and the mapping
between the machine interrupts (or traps) and the predefined
exceptions.
j. On a multi-processor, the rules governing the delivery of an
interrupt to a particular processor.
Implementation Permissions
1. If the underlying system or hardware does not allow interrupts to be
blocked, then no blocking is required as part of the execution of
subprograms of a protected object whose one of its subprograms is an
interrupt handler.
2. In a multi-processor with more than one interrupt subsystem, it is
implementation defined whether (and how) interrupt sources from separate
subsystems share the same Interrupt_ID type, see C.3.2. In particular,
the meaning of a blocked or pending interrupt may then be applicable to
one processor only.
3. Implementations are allowed to impose timing or other limitations on the
execution of interrupt handlers.
4. Other forms of handlers are allowed to be supported, in which case, the
rules of this subclause should be adhered to.
5. The active priority of the execution of an interrupt handler is allowed
to vary from one occurrence of the same interrupt to another.
Implementation Advice
6. If the Ceiling_Locking policy is not in effect, the implementation should
provide means for the application to specify which interrupts are to be
blocked during protected actions, if the underlying system allows for a
finer-grain control of interrupt blocking.
NOTES
7. (1) The default treatment for an interrupt can be to keep the interrupt
pending or to deliver it to an implementation-defined handler. Examples
of actions that an implementation-defined handler is allowed to perform
include aborting the partition, ignoring (i.e., discarding occurrences
of) the interrupt, or queuing one or more occurrences of the interrupt
for possible later delivery when a user-defined handler is attached to
that interrupt.
8. (2) It is a bounded error to call Task_Identification.Current_Task (see
C.7.1) from an interrupt handler.
9. (3) The rule that an exception propagated from an interrupt handler has
no effect is modeled after the rule about exceptions propagated out of
task bodies.
C.3.1 Protected Procedure Handlers
C.3.2 The Package Interrupts
ΓòÉΓòÉΓòÉ 19.3.1. Protected Procedure Handlers ΓòÉΓòÉΓòÉ
Syntax
1. The form of a pragma Interrupt_Handler is as follows:
2.
pragma Interrupt_Handler(handler_name);
3. The form of a pragma Attach_Handler is as follows:
4.
pragma Attach_Handler(handler_name, expression);
Name Resolution Rules
5. For the Interrupt_Handler and Attach_Handler pragmas, the handler_name
shall resolve to denote a protected procedure with a parameterless
profile.
6. For the Attach_Handler pragma, the expected type for the expression is
Interrupts.Interrupt_ID, see C.3.2.
Legality Rules
7. The Attach_Handler pragma is only allowed immediately within the
protected_definition where the corresponding subprogram is declared. The
corresponding protected_type_declaration or single_protected_declaration
shall be a library level declaration.
8. The Interrupt_Handler pragma is only allowed immediately within a
protected_definition. The corresponding protected_type_declaration shall
be a library level declaration. In addition, any object_declaration of
such a type shall be a library level declaration.
Dynamic Semantics
9. If the pragma Interrupt_Handler appears in a protected_definition, then
the corresponding procedure can be attached dynamically, as a handler, to
interrupts, see C.3.2. Such procedures are allowed to be attached to
multiple interrupts.
10. The expression in the Attach_Handler pragma as evaluated at object
creation time specifies an interrupt. As part of the initialization of
that object, if the Attach_Handler pragma is specified, the handler
procedure is attached to the specified interrupt. A check is made that
the corresponding interrupt is not reserved. Program_Error is raised if
the check fails, and the existing treatment for the interrupt is not
affected.
11. If the Ceiling_Locking policy, see D.3 is in effect then upon the
initialization of a protected object that either an Attach_Handler or
Interrupt_Handler pragma applies to one of its procedures, a check is
made that the ceiling priority defined in the protected_definition is in
the range of System.Interrupt_Priority. If the check fails, Program_Error
is raised.
12. When a protected object is finalized, for any of its procedures that are
attached to interrupts, the handler is detached. If the handler was
attached by a procedure in the Interrupts package or if no user handler
was previously attached to the interrupt, the default treatment is
restored. Otherwise, that is, if an Attach_Handler pragma was used, the
previous handler is restored.
13. When a handler is attached to an interrupt, the interrupt is blocked
(subject to the Implementation Permission in C.3, during the execution of
every protected action on the protected object containing the handler.
Erroneous Execution
14. If the Ceiling_Locking policy, see D.3, is in effect and an interrupt is
delivered to a handler, and the interrupt hardware priority is higher
than the ceiling priority of the corresponding protected object, the
execution of the program is erroneous.
Metrics
15. The following metric shall be documented by the implementation:
a. The worst case overhead for an interrupt handler that is a
parameterless protected procedure, in clock cycles. This is the
execution time not directly attributable to the handler procedure or
the interrupted execution. It is estimated as C - (A+B), where A is
how long it takes to complete a given sequence of instructions
without any interrupt, B is how long it takes to complete a normal
call to a given protected procedure, and C is how long it takes to
complete the same sequence of instructions when it is interrupted by
one execution of the same procedure called via an interrupt.
Implementation Permissions
1. When the pragmas Attach_Handler or Interrupt_Handler apply to a protected
procedure, the implementation is allowed to impose implementation-defined
restrictions on the corresponding protected_type_declaration and
protected_body.
2. An implementation may use a different mechanism for invoking a protected
procedure in response to a hardware interrupt than is used for a call to
that protected procedure from a task.
3. Notwithstanding what this subclause says elsewhere, the Attach_Handler
and Interrupt_Handler pragmas are allowed to be used for other,
implementation defined, forms of interrupt handlers.
Implementation Advice
4. Whenever possible, the implementation should allow interrupt handlers to
be called directly by the hardware.
5. Whenever practical, the implementation should detect violations of any
implementation-defined restrictions before run time.
NOTES
6. (4) The Attach_Handler pragma can provide static attachment of handlers
to interrupts if the implementation supports preelaboration of protected
objects (see C.4).
7. (5) The ceiling priority of a protected object that one of its procedures
is attached to an interrupt should be at least as high as the highest
processor priority at which that interrupt will ever be delivered.
8. (6) Protected procedures can also be attached dynamically to interrupts
via operations declared in the predefined package Interrupts.
9. (7) An example of a possible implementation-defined restriction is
disallowing the use of the standard storage pools within the body of a
protected procedure that is an interrupt handler.
ΓòÉΓòÉΓòÉ 19.3.2. The Package Interrupts ΓòÉΓòÉΓòÉ
Static Semantics
1. The following language-defined packages exist:
2.
with System;
package Ada.Interrupts is
type Interrupt_ID is implementation-defined;
type Parameterless_Handler is
access protected procedure;
1.
function Is_Reserved (Interrupt : Interrupt_ID)
return Boolean;
2.
function Is_Attached (Interrupt : Interrupt_ID)
return Boolean;
3.
function Current_Handler (Interrupt : Interrupt_ID)
return Parameterless_Handler;
4.
procedure Attach_Handler
(New_Handler : in Parameterless_Handler;
Interrupt : in Interrupt_ID);
5.
procedure Exchange_Handler
(Old_Handler : out Parameterless_Handler;
New_Handler : in Parameterless_Handler;
Interrupt : in Interrupt_ID);
6.
procedure Detach_Handler
(Interrupt : in Interrupt_ID);
7.
function Reference(Interrupt : Interrupt_ID)
return System.Address;
8.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Interrupts;
9.
package Ada.Interrupts.Names is
implementation-defined : constant Interrupt_ID :=
implementation-defined;
. . .
implementation-defined : constant Interrupt_ID :=
implementation-defined;
end Ada.Interrupts.Names;
Dynamic Semantics
10. The Interrupt_ID type is an implementation-defined discrete type used to
identify interrupts.
11. The Is_Reserved function returns True if and only if the specified
interrupt is reserved.
12. The Is_Attached function returns True if and only if a user-specified
interrupt handler is attached to the interrupt.
13. The Current_Handler function returns a value that represents the attached
handler of the interrupt. If no user-defined handler is attached to the
interrupt, Current_Handler returns a value that designates the default
treatment; calling Attach_Handler or Exchange_Handler with this value
restores the default treatment.
14. The Attach_Handler procedure attaches the specified handler to the
interrupt, overriding any existing treatment (including a user handler)
in effect for that interrupt. If New_Handler is null, the default
treatment is restored. If New_Handler designates a protected procedure to
which the pragma Interrupt_Handler does not apply, Program_Error is
raised. In this case, the operation does not modify the existing
interrupt treatment.
15. The Exchange_Handler procedure operates in the same manner as
Attach_Handler with the addition that the value returned in Old_Handler
designates the previous treatment for the specified interrupt.
16. The Detach_Handler procedure restores the default treatment for the
specified interrupt.
17. For all operations defined in this package that take a parameter of type
Interrupt_ID, with the exception of Is_Reserved and Reference, a check is
made that the specified interrupt is not reserved. Program_Error is
raised if this check fails.
18. If, by using the Attach_Handler, Detach_Handler, or Exchange_Handler
procedures, an attempt is made to detach a handler that was attached
statically (using the pragma Attach_Handler), the handler is not detached
and Program_Error is raised.
19. The Reference function returns a value of type System.Address that can be
used to attach a task entry, via an address clause, see J.7.1, to
theinterrupt specified by Interrupt. This function raises Program_Error
if attaching task entries to interrupts (or to this particular interrupt)
is not supported.
Implementation Requirements
20. At no time during attachment or exchange of handlers shall the current
handler of the corresponding interrupt be undefined.
Documentation Requirements
21. If the Ceiling_Locking policy, see D.3, is in effect the implementation
shall document the default ceiling priority assigned to a protected
object that contains either the Attach_Handler or Interrupt_Handler
pragmas, but not the Interrupt_Priority pragma. This default need not be
the same for all interrupts.
Implementation Advice
22. If implementation-defined forms of interrupt handler procedures are
supported, such as protected procedures with parameters, then for each
such form of a handler, a type analogous to Parameterless_Handler should
be specified in a child package of Interrupts, with the same operations
as in the predefined package Interrupts.
NOTES
23. (8) The package Interrupts.Names contains implementation-defined names
(and constant values) for the interrupts that are supported by the
implementation.
Examples
24. Example of interrupt handlers:
25.
Device_Priority : constant
array (1┬╖┬╖5) of System.Interrupt_Priority := ( ┬╖┬╖┬╖ );
protected type Device_Interface
(Int_ID : Ada.Interrupts.Interrupt_ID) is
procedure Handler;
pragma Attach_Handler(Handler, Int_ID);
┬╖┬╖┬╖
pragma Interrupt_Priority(Device_Priority(Int_ID));
end Device_Interface;
┬╖┬╖┬╖
Device_1_Driver : Device_Interface(1);
┬╖┬╖┬╖
Device_5_Driver : Device_Interface(5);
┬╖┬╖┬╖
ΓòÉΓòÉΓòÉ 19.4. Preelaboration Requirements ΓòÉΓòÉΓòÉ
1. This clause specifies additional implementation and documentation
requirements for the Preelaborate pragma, see 10.2.1.
Implementation Requirements
2. The implementation shall not incur any run-time overhead for the
elaboration checks of subprograms and protected_bodies declared in
preelaborated library units.
3. The implementation shall not execute any memory write operations after
load time for the elaboration of constant objects declared immediately
within the declarative region of a preelaborated library package, so long
as the subtype and initial expression (or default initial expressions if
initialized by default) of the object_declaration satisfy the following
restrictions. The meaning of load time is implementation defined.
a. Any subtype_mark denotes a statically constrained subtype, with
statically constrained subcomponents, if any;
b. any constraint is a static constraint;
c. any allocator is for an access-to-constant type;
d. any uses of predefined operators appear only within static
expressions;
e. any primaries that are names, other than attribute_references for
the Access or Address attributes, appear only within static
expressions;
f. any name that is not part of a static expression is an expanded name
or direct_name that statically denotes some entity;
g. any discrete_choice of an array_aggregate is static;
h. no language-defined check associated with the elaboration of the
object_declaration can fail.
Documentation Requirements
1. The implementation shall document any circumstances under which the
elaboration of a preelaborated package causes code to be executed at run
time.
2. The implementation shall document whether the method used for
initialization of preelaborated variables allows a partition to be
restarted without reloading.
Implementation Advice
3. It is recommended that preelaborated packages be implemented in such a
way that there should be little or no code executed at run time for the
elaboration of entities not already covered by the Implementation
Requirements.
ΓòÉΓòÉΓòÉ 19.5. Pragma Discard_Names ΓòÉΓòÉΓòÉ
1. A pragma Discard_Names may be used to request a reduction in storage used
for the names of certain entities.
Syntax
2. The form of a pragma Discard_Names is as follows:
3.
pragma Discard_Names[([On => ] local_name)];
a. A pragma Discard_Names is allowed only immediately within a
declarative_part, immediately within a package_specification, or as
a configuration pragma.
Legality Rules
1. The local_name (if present) shall denote a non-derived enumeration first
subtype, a tagged first subtype, or an exception. The pragma applies to
the type or exception. Without a local_name, the pragma applies to all
such entities declared after the pragma, within the same declarative
region. Alternatively, the pragma can be used as a configuration pragma.
If the pragma applies to a type, then it applies also to all descendants
of the type.
Static Semantics
2. If a local_name is given, then a pragma Discard_Names is a representation
pragma.
3. If the pragma applies to an enumeration type, then the semantics of the
Wide_Image and Wide_Value attributes are implementation defined for that
type; the semantics of Image and Value are still defined in terms of
Wide_Image and Wide_Value. In addition, the semantics of
Text_IO.Enumeration_IO are implementation defined. If the pragma applies
to a tagged type, then the semantics of the Tags.Expanded_Name function
are implementation defined for that type. If the pragma applies to an
exception, then the semantics of the Exceptions.Exception_Name function
are implementation defined for that exception.
Implementation Advice
4. If the pragma applies to an entity, then the implementation should reduce
the amount of storage used for storing names associated with that entity.
ΓòÉΓòÉΓòÉ 19.6. Shared Variable Control ΓòÉΓòÉΓòÉ
1. This clause specifies representation pragmas that control the use of
shared variables.
Syntax
2. The form for pragmas Atomic, Volatile, Atomic_Components, and
Volatile_Components is as follows:
3.
pragma Atomic(local_name);
4.
pragma Volatile(local_name);
5.
pragma Atomic_Components(array_local_name);
6.
pragma Volatile_Components(array_local_name);
7. An atomic type is one to which a pragma Atomic applies. An atomic object
(including a component) is one to which a pragma Atomic applies, or a
component of an array to which a pragma Atomic_Components applies, or any
object of an atomic type.
8. A volatile type is one to which a pragma Volatile applies. A volatile
object (including a component) is one to which a pragma Volatile applies,
or a component of an array to which a pragma Volatile_Components applies,
or any object of a volatile type. In addition, every atomic type or
object is also defined to be volatile. Finally, if an object is volatile,
then so are all of its subcomponents (the same does not apply to atomic).
Name Resolution Rules
9. The local_name in an Atomic or Volatile pragma shall resolve to denote
either an object_declaration, a non-inherited component_declaration, or a
full_type_declaration. The array_local_name in an Atomic_Components or
Volatile_Components pragma shall resolve to denote the declaration of an
array type or an array object of an anonymous type.
Legality Rules
10. It is illegal to apply either an Atomic or Atomic_Components pragma to an
object or type if the implementation cannot support the indivisible reads
and updates required by the pragma (see below).
11. It is illegal to specify the Size attribute of an atomic object, the
Component_Size attribute for an array type with atomic components, or the
layout attributes of an atomic component, in a way that prevents the
implementation from performing the required indivisible reads and
updates.
12. If an atomic object is passed as a parameter, then the type of the formal
parameter shall either be atomic or allow pass by copy (that is, not be a
nonatomic by-reference type). If an atomic object is used as an actual
for a generic formal object of mode in out, then the type of the generic
formal object shall be atomic. If the prefix of an attribute_reference
for an Access attribute denotes an atomic object (including a component),
then the designated type of the resulting access type shall be atomic. If
an atomic type is used as an actual for a generic formal derived type,
then the ancestor of the formal type shall be atomic or allow pass by
copy. Corresponding rules apply to volatile objects and types.
13. If a pragma Volatile, Volatile_Components, Atomic, or Atomic_Components
applies to a stand-alone constant object, then a pragma Import shall also
apply to it.
Static Semantics
14. These pragmas are representation pragmas, see 13.1.
Dynamic Semantics
15. For an atomic object (including an atomic component) all reads and
updates of the object as a whole are indivisible.
16. For a volatile object all reads and updates of the object as a whole are
performed directly to memory.
17. Two actions are sequential, see 9.10, if each is the read or update of
the same atomic object.
18. If a type is atomic or volatile and it is not a by-copy type, then the
type is defined to be a by-reference type. If any subcomponent of a type
is atomic or volatile, then the type is defined to be a by-reference
type.
19. If an actual parameter is atomic or volatile, and the corresponding
formal parameter is not, then the parameter is passed by copy.
Implementation Requirements
20. The external effect of a program, see 1.1.3, is defined to include each
read and update of a volatile or atomic object. The implementation shall
not generate any memory reads or updates of atomic or volatile objects
other than those specified by the program.
21. If a pragma Pack applies to a type any of whose subcomponents are atomic,
the implementation shall not pack the atomic subcomponents more tightly
than that for which it can support indivisible reads and updates.
NOTES
22. (9) An imported volatile or atomic constant behaves as a constant (i.e.
read-only) with respect to other parts of the Ada program, but can still
be modified by an ``external source.''
ΓòÉΓòÉΓòÉ 19.7. Task Identification and Attributes ΓòÉΓòÉΓòÉ
1. This clause describes operations and attributes that can be used to
obtain the identity of a task. In addition, a package that associates
user-defined information with a task is defined.
C.7.1 The Package Task_Identification
C.7.2 The Package Task_Attributes
ΓòÉΓòÉΓòÉ 19.7.1. The Package Task_Identification ΓòÉΓòÉΓòÉ
Static Semantics
1. The following language-defined library package exists:
2.
package Ada.Task_Identification is
type Task_ID is private;
Null_Task_ID : constant Task_ID;
function "=" (Left, Right : Task_ID) return Boolean;
3.
function Image (T : Task_ID) return String;
function Current_Task return Task_ID;
procedure Abort_Task (T : in out Task_ID);
4.
function Is_Terminated(T : Task_ID) return Boolean;
function Is_Callable (T : Task_ID) return Boolean;
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Task_Identification;
Dynamic Semantics
5. A value of the type Task_ID identifies an existent task. The constant
Null_Task_ID does not identify any task. Each object of the type Task_ID
is default initialized to the value of Null_Task_ID.
6. The function "=" returns True if and only if Left and Right identify the
same task or both have the value Null_Task_ID.
7. The function Image returns an implementation-defined string that
identifies T. If T equals Null_Task_ID, Image returns an empty string.
8. The function Current_Task returns a value that identifies the calling
task.
9. The effect of Abort_Task is the same as the abort_statement for the task
identified by T. In addition, if T identifies the environment task, the
entire partition is aborted, see E.1.
10. The functions Is_Terminated and Is_Callable return the value of the
corresponding attribute of the task identified by T.
11. For a prefix T that is of a task type (after any implicit dereference),
the following attribute is defined:
12. T'Identity
13.
Yields a value of the type Task_ID that identifies the task
denoted by T.
14. For a prefix E that denotes an entry_declaration, the following attribute
is defined:
15. E'Caller
Yields a value of the type Task_ID that identifies the task
whose call is now being serviced. Use of this attribute is
allowed only inside an entry_body or accept_statement
corresponding to the entry_declaration denoted by E.
16. Program_Error is raised if a value of Null_Task_ID is passed as a
parameter to Abort_Task, Is_Terminated, and Is_Callable.
17. Abort_Task is a potentially blocking operation, see 9.5.1.
Bounded (Run-Time) Errors
18. It is a bounded error to call the Current_Task function from an entry
body or an interrupt handler. Program_Error is raised, or an
implementation-defined value of the type Task_ID is returned.
Erroneous Execution
19. If a value of Task_ID is passed as a parameter to any of the operations
declared in this package (or any language-defined child of this package),
and the corresponding task object no longer exists, the execution of the
program is erroneous.
Documentation Requirements
20. The implementation shall document the effect of calling Current_Task from
an entry body or interrupt handler.
NOTES
21. (10) This package is intended for use in writing user-defined task
scheduling packages and constructing server tasks. Current_Task can be
used in conjunction with other operations requiring a task as an argument
such as Set_Priority, see D.5.
22. (11) The function Current_Task and the attribute Caller can return a
Task_ID value that identifies the environment task.
ΓòÉΓòÉΓòÉ 19.7.2. The Package Task_Attributes ΓòÉΓòÉΓòÉ
Static Semantics
1. The following language-defined generic library package exists:
2.
with Ada.Task_Identification; use Ada.Task_Identification;
generic
type Attribute is private;
Initial_Value : in Attribute;
package Ada.Task_Attributes is
3.
type Attribute_Handle is access all Attribute;
4.
function Value(T : Task_ID := Current_Task)
return Attribute;
5.
function Reference(T : Task_ID := Current_Task)
return Attribute_Handle;
6.
procedure Set_Value(Val : in Attribute;
T : in Task_ID := Current_Task);
procedure Reinitialize(T : in Task_ID := Current_Task);
7.
end Ada.Task_Attributes;
Dynamic Semantics
8. When an instance of Task_Attributes is elaborated in a given active
partition, an object of the actual type corresponding to the formal type
Attribute is implicitly created for each task (of that partition) that
exists and is not yet terminated. This object acts as a user-defined
attribute of the task. A task created previously in the partition and not
yet terminated has this attribute from that point on. Each task
subsequently created in the partition will have this attribute when
created. In all these cases, the initial value of the given attribute is
Initial_Value.
9. The Value operation returns the value of the corresponding attribute of
T.
10. The Reference operation returns an access value that designates the
corresponding attribute of T.
11. The Set_Value operation performs any finalization on the old value of the
attribute of T and assigns Val to that attribute, see 5.2, and 7.6.
12. The effect of the Reinitialize operation is the same as Set_Value where
the Val parameter is replaced with Initial_Value.
13. For all the operations declared in this package, Tasking_Error is raised
if the task identified by T is terminated. Program_Error is raised if the
value of T is Null_Task_ID.
Erroneous Execution
14. It is erroneous to dereference the access value returned by a given call
on Reference after a subsequent call on Reinitialize for the same task
attribute, or after the associated task terminates.
15. If a value of Task_ID is passed as a parameter to any of the operations
declared in this package and the corresponding task object no longer
exists, the execution of the program is erroneous.
Implementation Requirements
16. The implementation shall perform each of the above operations for a given
attribute of a given task atomically with respect to any other of the
above operations for the same attribute of the same task.
17. When a task terminates, the implementation shall finalize all attributes
of the task, and reclaim any other storage associated with the
attributes.
Documentation Requirements
18. The implementation shall document the limit on the number of attributes
per task, if any, and the limit on the total storage for attribute values
per task, if such a limit exists.
19. In addition, if these limits can be configured, the implementation shall
document how to configure them.
Metrics
20. The implementation shall document the following metrics: A task calling
the following subprograms shall execute in a sufficiently high priority
as to not be preempted during the measurement period. This period shall
start just before issuing the call and end just after the call completes.
If the attributes of task T are accessed by the measurement tests, no
other task shall access attributes of that task during the measurement
period. For all measurements described here, the Attribute type shall be
a scalar whose size is equal to the size of the predefined integer size.
For each measurement, two cases shall be documented: one where the
accessed attributes are of the calling task (that is, the default value
for the T parameter is used), and the other, where T identifies another,
non-terminated, task.
21. The following calls (to subprograms in the Task_Attributes package) shall
be measured:
a. a call to Value, where the return value is Initial_Value;
b. a call to Value, where the return value is not equal to
Initial_Value;
c. a call to Reference, where the return value designates a value equal
to Initial_Value;
d. a call to Reference, where the return value designates a value not
equal to Initial_Value;
e. a call to Set_Value where the Val parameter is not equal to
Initial_Value and the old attribute value is equal to Initial_Value.
f. a call to Set_Value where the Val parameter is not equal to
Initial_Value and the old attribute value is not equal to
Initial_Value.
Implementation Permissions
1. An implementation need not actually create the object corresponding to a
task attribute until its value is set to something other than that of
Initial_Value, or until Reference is called for the task attribute.
Similarly, when the value of the attribute is to be reinitialized to that
of Initial_Value, the object may instead be finalized and its storage
reclaimed, to be recreated when needed later. While the object does not
exist, the function Value may simply return Initial_Value, rather than
implicitly creating the object.
2. An implementation is allowed to place restrictions on the maximum number
of attributes a task may have, the maximum size of each attribute, and
the total storage size allocated for all the attributes of a task.
Implementation Advice
3. Some implementations are targeted to domains in which memory use at run
time must be completely deterministic. For such implementations, it is
recommended that the storage for task attributes will be pre-allocated
statically and not from the heap. This can be accomplished by either
placing restrictions on the number and the size of the task's attributes,
or by using the pre-allocated storage for the first N attribute objects,
and the heap for the others. In the latter case, N should be documented.
NOTES
4. (12) An attribute always exists (after instantiation), and has the
initial value. It need not occupy memory until the first operation that
potentially changes the attribute value. The same holds true after
Reinitialize.
5. (13) The result of the Reference function should be used with care; it is
always safe to use that result in the task body whose attribute is being
accessed. However, when the result is being used by another task, the
programmer must make sure that the task whose attribute is being accessed
is not yet terminated. Failing to do so could make the program execution
erroneous.
6. (14) As specified in C.7.1, if the parameter T (in a call on a subprogram
of an instance of this package) identifies a nonexistent task, the
execution of the program is erroneous.
ΓòÉΓòÉΓòÉ 20. Real-Time Systems (normative) ΓòÉΓòÉΓòÉ
1. This Annex specifies additional characteristics of Ada implementations
intended for real-time systems software. To conform to this Annex, an
implementation shall also conform to the Systems Programming Annex.
Metrics
2. The metrics are documentation requirements; an implementation shall
document the values of the language-defined metrics for at least one
configuration of hardware or an underlying system supported by the
implementation, and shall document the details of that configuration.
3. The metrics do not necessarily yield a simple number. For some, a range
is more suitable, for others a formula dependent on some parameter is
appropriate, and for others, it may be more suitable to break the metric
into several cases. Unless specified otherwise, the metrics in this annex
are expressed in processor clock cycles. For metrics that require
documentation of an upper bound, if there is no upper bound, the
implementation shall report that the metric is unbounded.
NOTES
4. (1) The specification of the metrics makes a distinction between upper
bounds and simple execution times. Where something is just specified as
``the execution time of'' a piece of code, this leaves one the freedom to
choose a nonpathological case. This kind of metric is of the form ``there
exists a program such that the value of the metric is V''. Conversely,
the meaning of upper bounds is ``there is no program such that the value
of the metric is greater than V''. This kind of metric can only be
partially tested, by finding the value of V for one or more test
programs.
5. (2) The metrics do not cover the whole language; they are limited to
features that are specified in C: ``Systems Programming'', and in this
Annex. The metrics are intended to provide guidance to potential users as
to whether a particular implementation of such a feature is going to be
adequate for a particular real-time application. As such, the metrics are
aimed at known implementation choices that can result in significant
performance differences.
6. (3) The purpose of the metrics is not necessarily to provide fine-grained
quantitative results or to serve as a comparison between different
implementations on the same or different platforms. Instead, their goal
is rather qualitative; to define a standard set of approximate values
that can be measured and used to estimate the general suitability of an
implementation, or to evaluate the comparative utility of certain
features of an implementation for a particular real-time application.
D.1 Task Priorities
D.2 Priority Scheduling
D.3 Priority Ceiling Locking
D.4 Entry Queuing Policies
D.5 Dynamic Priorities
D.6 Preemptive Abort
D.7 Tasking Restrictions
D.8 Monotonic Time
D.9 Delay Accuracy
D.10 Synchronous Task Control
D.11 Asynchronous Task Control
D.12 Other Optimizations and Determinism Rules ---
The Detailed Node Listing ---
D.1 Task Priorities
D.2 Priority Scheduling
D.2.1 The Task Dispatching Model
D.2.2 The Standard Task Dispatching Policy
D.3 Priority Ceiling Locking
D.4 Entry Queuing Policies
D.5 Dynamic Priorities
D.6 Preemptive Abort
D.7 Tasking Restrictions
D.8 Monotonic Time
D.9 Delay Accuracy
D.10 Synchronous Task Control
D.11 Asynchronous Task Control
D.12 Other Optimizations and Determinism Rules
ΓòÉΓòÉΓòÉ 20.1. Task Priorities ΓòÉΓòÉΓòÉ
1. This clause specifies the priority model for real-time systems. In
addition, the methods for specifying priorities are defined.
Syntax
2. The form of a pragma Priority is as follows:
3.
pragma Priority(expression);
4. The form of a pragma Interrupt_Priority is as follows:
5.
pragma Interrupt_Priority[(expression)];
Name Resolution Rules
6. The expected type for the expression in a Priority or Interrupt_Priority
pragma is Integer.
Legality Rules
7. A Priority pragma is allowed only immediately within a task_definition, a
protected_definition, or the declarative_part of a subprogram_body. An
Interrupt_Priority pragma is allowed only immediately within a task_
definition or a protected_definition. At most one such pragma shall
appear within a given construct.
8. For a Priority pragma that appears in the declarative_part of a
subprogram_body, the expression shall be static, and its value shall be
in the range of System.Priority.
Static Semantics
9. The following declarations exist in package System:
10.
subtype Any_Priority is Integer range implementation-defined;
subtype Priority is Any_Priority range
Any_Priority'First ┬╖┬╖ implementation-defined;
subtype Interrupt_Priority is Any_Priority range
Priority'Last+1 ┬╖┬╖ Any_Priority'Last;
11.
Default_Priority : constant Priority
:= (Priority'First + Priority'Last)/2;
12. The full range of priority values supported by an implementation is
specified by the subtype Any_Priority. The subrange of priority values
that are high enough to require the blocking of one or more interrupts is
specified by the subtype Interrupt_Priority. The subrange of priority
values below System.Interrupt_Priority'First is specified by the subtype
System.Priority.
13. The priority specified by a Priority or Interrupt_Priority pragma is the
value of the expression in the pragma, if any. If there is no expression
in an Interrupt_Priority pragma, the priority value is
Interrupt_Priority'Last.
Dynamic Semantics
14. A Priority pragma has no effect if it occurs in the declarative_part of
the subprogram_body of a subprogram other than the main subprogram.
15. A task priority is an integer value that indicates a degree of urgency
and is the basis for resolving competing demands of tasks for resources.
Unless otherwise specified, whenever tasks compete for processors or
other implementation-defined resources, the resources are allocated to
the task with the highest priority value. The base priority of a task is
the priority with which it was created, or to which it was later set by
Dynamic_Priorities.Set_Priority, see D.5. At all times, a task also has
an active priority, which generally reflects its base priority as well as
any priority it inherits from other sources. Priority inheritance is the
process by which the priority of a task or other entity (e.g. a protected
object, see D.3) is used in the evaluation of another task's active
priority.
16. The effect of specifying such a pragma in a protected_definition is
discussed in D.3.
17. The expression in a Priority or Interrupt_Priority pragma that appears in
a task_definition is evaluated for each task object, see 9.1. For a
Priority pragma, the value of the expression is converted to the subtype
Priority; for an Interrupt_Priority pragma, this value is converted to
the subtype Any_Priority. The priority value is then associated with the
task object whose task_definition contains the pragma.
18. Likewise, the priority value is associated with the environment task if
the pragma appears in the declarative_part of the main subprogram.
19. The initial value of a task's base priority is specified by default or by
means of a Priority or Interrupt_Priority pragma. After a task is
created, its base priority can be changed only by a call to
Dynamic_Priorities.Set_Priority, see D.5. The initial base priority of a
task in the absence of a pragma is the base priority of the task that
creates it at the time of creation, see 9.1. If a pragma Priority does
not apply to the main subprogram, the initial base priority of the
environment task is System.Default_Priority. The task's active priority
is used when the task competes for processors. Similarly, the task's
active priority is used to determine the task's position in any queue
when Priority_Queuing is specified, see D.4.
20. At any time, the active priority of a task is the maximum of all the
priorities the task is inheriting at that instant. For a task that is not
held, see D.11, its base priority is always a source of priority
inheritance. Other sources of priority inheritance are specified under
the following conditions:
a. During activation, a task being activated inherits the active
priority of the its activator, see 9.2.
b. During rendezvous, the task accepting the entry call inherits the
active priority of the caller, see 9.5.3.
c. During a protected action on a protected object, a task inherits the
ceiling priority of the protected object, see 9.5, and D.3.
1. In all of these cases, the priority ceases to be inherited as soon as the
condition calling for the inheritance no longer exists.
Implementation Requirements
2. The range of System.Interrupt_Priority shall include at least one value.
3. The range of System.Priority shall include at least 30 values.
NOTES
4. (4) The priority expression can include references to discriminants of
the enclosing type.
5. (5) It is a consequence of the active priority rules that at the point
when a task stops inheriting a priority from another source, its active
priority is re-evaluated. This is in addition to other instances
described in this Annex for such re-evaluation.
6. (6) An implementation may provide a non-standard mode in which tasks
inherit priorities under conditions other than those specified above.
ΓòÉΓòÉΓòÉ 20.2. Priority Scheduling ΓòÉΓòÉΓòÉ
1. This clause describes the rules that determine which task is selected for
execution when more than one task is ready, see 9.2. The rules have two
parts: the task dispatching model, see D.2.1, and a specific task
dispatching policy, see D.2.2.
D.2.1 The Task Dispatching Model
D.2.2 The Standard Task Dispatching Policy
ΓòÉΓòÉΓòÉ 20.2.1. The Task Dispatching Model ΓòÉΓòÉΓòÉ
1. The task dispatching model specifies preemptive scheduling, based on
conceptual priority-ordered ready queues.
Dynamic Semantics
2. A task runs (that is, it becomes a running task) only when it is ready
(see 9.2) and the execution resources required by that task are
available. Processors are allocated to tasks based on each task's active
priority.
3. It is implementation defined whether, on a multiprocessor, a task that is
waiting for access to a protected object keeps its processor busy.
4. Task dispatching is the process by which one ready task is selected for
execution on a processor. This selection is done at certain points during
the execution of a task called task dispatching points. A task reaches a
task dispatching point whenever it becomes blocked, and whenever it
becomes ready. In addition, the completion of an accept_statement, see
9.5.2, and task termination are task dispatching points for the executing
task. Other task dispatching points are defined throughout this Annex.
5. Task dispatching policies are specified in terms of conceptual ready
queues, task states, and task preemption. A ready queue is an ordered
list of ready tasks. The first position in a queue is called the head of
the queue, and the last position is called the tail of the queue. A task
is ready if it is in a ready queue, or if it is running. Each processor
has one ready queue for each priority value. At any instant, each ready
queue of a processor contains exactly the set of tasks of that priority
that are ready for execution on that processor, but are not running on
any processor; that is, those tasks that are ready, are not running on
any processor, and can be executed using that processor and other
available resources. A task can be on the ready queues of more than one
processor.
6. Each processor also has one running task, which is the task currently
being executed by that processor. Whenever a task running on a processor
reaches a task dispatching point, one task is selected to run on that
processor. The task selected is the one at the head of the highest
priority nonempty ready queue; this task is then removed from all ready
queues to which it belongs.
7. A preemptible resource is a resource that while allocated to one task can
be allocated (temporarily) to another instead. Processors are preemptible
resources. Access to a protected object, see 9.5.1, is a nonpreemptible
resource. When a higher-priority task is dispatched to the processor, and
the previously running task is placed on the appropriate ready queue, the
latter task is said to be preempted.
8. A new running task is also selected whenever there is a nonempty ready
queue with a higher priority than the priority of the running task, or
when the task dispatching policy requires a running task to go back to a
ready queue. These are also task dispatching points.
Implementation Permissions
9. An implementation is allowed to define additional resources as execution
resources, and to define the corresponding allocation policies for them.
Such resources may have an implementation defined effect on task
dispatching, see D.2.2.
10. An implementation may place implementation-defined restrictions on tasks
whose active priority is in the Interrupt_Priority range.
NOTES
11. (7) Section 9 specifies under which circumstances a task becomes ready.
The ready state is affected by the rules for task activation and
termination, delay statements, and entry calls. When a task is not ready,
it is said to be blocked.
12. (8) An example of a possible implementation-defined execution resource is
a page of physical memory, which needs to be loaded with a particular
page of virtual memory before a task can continue execution.
13. (9) The ready queues are purely conceptual; there is no requirement that
such lists physically exist in an implementation.
14. (10) While a task is running, it is not on any ready queue. Any time the
task that is running on a processor is added to a ready queue, a new
running task is selected for that processor.
15. (11) In a multiprocessor system, a task can be on the ready queues of
more than one processor. At the extreme, if several processors share the
same set of ready tasks, the contents of their ready queues is identical,
and so they can be viewed as sharing one ready queue, and can be
implemented that way. Thus, the dispatching model covers multiprocessors
where dispatching is implemented using a single ready queue, as well as
those with separate dispatching domains.
16. (12) The priority of a task is determined by rules specified in this
subclause, and under D.1: ``Task Priorities'', D.3: ``Priority Ceiling
Locking'', and D.5: ``Dynamic Priorities''.
ΓòÉΓòÉΓòÉ 20.2.2. The Standard Task Dispatching Policy ΓòÉΓòÉΓòÉ
Syntax
1. The form of a pragma Task_Dispatching_Policy is as follows:
2.
pragma Task_Dispatching_Policy(policy_identifier );
Legality Rules
3. The policy_identifier shall either be FIFO_Within_Priorities or an
implementation-defined identifier.
Post-Compilation Rules
4. A Task_Dispatching_Policy pragma is a configuration pragma.
5. If the FIFO_Within_Priorities policy is specified for a partition, then
the Ceiling_Locking policy, see D.3 shall also be specified for the
partition.
Dynamic Semantics
6. A task dispatching policy specifies the details of task dispatching that
are not covered by the basic task dispatching model. These rules govern
when tasks are inserted into and deleted from the ready queues, and
whether a task is inserted at the head or the tail of the queue for its
active priority. The task dispatching policy is specified by a
Task_Dispatching_Policy configuration pragma. If no such pragma appears
in any of the program units comprising a partition, the task dispatching
policy for that partition is unspecified.
7. The language defines only one task dispatching policy,
FIFO_Within_Priorities; when this policy is in effect, modifications to
the ready queues occur only as follows:
a. When a blocked task becomes ready, it is added at the tail of the
ready queue for its active priority.
b. When the active priority of a ready task that is not running
changes, or the setting of its base priority takes effect, the task
is removed from the ready queue for its old active priority and is
added at the tail of the ready queue for its new active priority,
except in the case where the active priority is lowered due to the
loss of inherited priority, in which case the task is added at the
head of the ready queue for its new active priority.
c. When the setting of the base priority of a running task takes
effect, the task is added to the tail of the ready queue for its
active priority.
d. When a task executes a delay_statement that does not result in
blocking, it is added to the tail of the ready queue for its active
priority.
1. Each of the events specified above is a task dispatching point (see
D.2.1).
2. In addition, when a task is preempted, it is added at the head of the
ready queue for its active priority.
Documentation Requirements
3. Priority inversion is the duration for which a task remains at the head
of the highest priority ready queue while the processor executes a lower
priority task. The implementation shall document:
a. The maximum priority inversion a user task can experience due to
activity of the implementation (on behalf of lower priority tasks),
and
b. whether execution of a task can be preempted by the implementation
processing of delay expirations for lower priority tasks, and if so,
for how long.
Implementation Permissions
1. Implementations are allowed to define other task dispatching policies,
but need not support more than one such policy per partition.
2. For optimization purposes, an implementation may alter the points at
which task dispatching occurs, in an implementation defined manner.
However, a delay_statement always corresponds to at least one task
dispatching point.
NOTES
3. (13) If the active priority of a running task is lowered due to loss of
inherited priority (as it is on completion of a protected operation) and
there is a ready task of the same active priority that is not running,
the running task continues to run (provided that there is no higher
priority task).
4. (14) The setting of a task's base priority as a result of a call to
Set_Priority does not always take effect immediately when Set_Priority is
called. The effect of setting the task's base priority is deferred while
the affected task performs a protected action.
5. (15) Setting the base priority of a ready task causes the task to move to
the end of the queue for its active priority, regardless of whether the
active priority of the task actually changes.
ΓòÉΓòÉΓòÉ 20.3. Priority Ceiling Locking ΓòÉΓòÉΓòÉ
1. This clause specifies the interactions between priority task scheduling
and protected object ceilings. This interaction is based on the concept
of the ceiling priority of a protected object.
Syntax
2. The form of a pragma Locking_Policy is as follows:
3.
pragma Locking_Policy(policy_identifier);
Legality Rules
4. The policy_identifier shall either be Ceiling_Locking or an
implementation-defined identifier.
Post-Compilation Rules
5. A Locking_Policy pragma is a configuration pragma.
Dynamic Semantics
6. A locking policy specifies the details of protected object locking. These
rules specify whether or not protected objects have priorities, and the
relationships between these priorities and task priorities. In addition,
the policy specifies the state of a task when it executes a protected
action, and how its active priority is affected by the locking. The
locking policy is specified by a Locking_Policy pragma. For
implementation-defined locking policies, the effect of a Priority or
Interrupt_Priority pragma on a protected object is implementation
defined. If no Locking_Policy pragma appears in any of the program units
comprising a partition, the locking policy for that partition, as well as
the effect of specifying either a Priority or Interrupt_Priority pragma
for a protected object, are implementation defined.
7. There is one predefined locking policy, Ceiling_Locking; this policy is
defined as follows:
a. Every protected object has a ceiling priority, which is determined
by either a Priority or Interrupt_Priority pragma as defined in D.1.
The ceiling priority of a protected object (or ceiling, for short)
is an upper bound on the active priority a task can have when it
calls protected operations of that protected object.
b. The expression of a Priority or Interrupt_Priority pragma is
evaluated as part of the creation of the corresponding protected
object and converted to the subtype System.Any_Priority or
System.Interrupt_Priority, respectively. The value of the expression
is the ceiling priority of the corresponding protected object.
c. If an Interrupt_Handler or Attach_Handler pragma, see C.3.1, appears
in a protected_definition without an Interrupt_Priority pragma, the
ceiling priority of protected objects of that type is implementation
defined, but in the range of the subtype System.Interrupt_Priority.
d. If no pragma Priority, Interrupt_Priority, Interrupt_Handler, or
Attach_Handler is specified in the protected_definition, then the
ceiling priority of the corresponding protected object is
System.Priority'Last.
e. While a task executes a protected action, it inherits the ceiling
priority of the corresponding protected object.
f. When a task calls a protected operation, a check is made that its
active priority is not higher than the ceiling of the corresponding
protected object; Program_Error is raised if this check fails.
Implementation Permissions
1. The implementation is allowed to round all ceilings in a certain subrange
of System.Priority or System.Interrupt_Priority up to the top of that
subrange, uniformly.
2. Implementations are allowed to define other locking policies, but need
not support more than one such policy per partition.
3. Since implementations are allowed to place restrictions on code that runs
at an interrupt-level active priority, see C.3.1, and D.2.1, the
implementation may implement a language feature in terms of a protected
object with an implementation-defined ceiling, but the ceiling shall be
no less than Priority'Last.
Implementation Advice
4. The implementation should use names that end with ``_Locking'' for
implementation-defined locking policies.
NOTES
5. (16) While a task executes in a protected action, it can be preempted
only by tasks whose active priorities are higher than the ceiling
priority of the protected object.
6. (17) If a protected object has a ceiling priority in the range of
Interrupt_Priority, certain interrupts are blocked while protected
actions of that object execute. In the extreme, if the ceiling is
Interrupt_Priority'Last, all blockable interrupts are blocked during that
time.
7. (18) The ceiling priority of a protected object has to be in the
Interrupt_Priority range if one of its procedures is to be used as an
interrupt handler, see C.3.
8. (19) When specifying the ceiling of a protected object, one should choose
a value that is at least as high as the highest active priority at which
tasks can be executing when they call protected operations of that
object. In determining this value the following factors, which can affect
active priority, should be considered: the effect of Set_Priority, nested
protected operations, entry calls, task activation, and other
implementation-defined factors.
9. (20) Attaching a protected procedure whose ceiling is below the interrupt
hardware priority to an interrupt causes the execution of the program to
be erroneous, see C.3.1.
10. (21) On a single processor implementation, the ceiling priority rules
guarantee that there is no possibility of deadlock involving only
protected subprograms (excluding the case where a protected operation
calls another protected operation on the same protected object).
ΓòÉΓòÉΓòÉ 20.4. Entry Queuing Policies ΓòÉΓòÉΓòÉ
1. This clause specifies a mechanism for a user to choose an entry queuing
policy. It also defines one such policy. Other policies are
implementation defined.
Syntax
2. The form of a pragma Queuing_Policy is as follows:
3.
pragma Queuing_Policy(policy_identifier);
Legality Rules
4. The policy_identifier shall be either FIFO_Queuing, Priority_Queuing or
an implementation-defined identifier.
Post-Compilation Rules
5. A Queuing_Policy pragma is a configuration pragma.
Dynamic Semantics
6. A queuing policy governs the order in which tasks are queued for entry
service, and the order in which different entry queues are considered for
service. The queuing policy is specified by a Queuing_Policy pragma.
7. Two queuing policies, FIFO_Queuing and Priority_Queuing, are language
defined. If no Queuing_Policy pragma appears in any of the program units
comprising the partition, the queuing policy for that partition is
FIFO_Queuing. The rules for this policy are specified in 9.5.3, and
9.7.1.
8. The Priority_Queuing policy is defined as follows:
a. The calls to an entry (including a member of an entry family) are
queued in an order consistent with the priorities of the calls. The
priority of an entry call is initialized from the active priority of
the calling task at the time the call is made, but can change later.
Within the same priority, the order is consistent with the calling
(or requeuing, or priority setting) time (that is, a FIFO order).
b. After a call is first queued, changes to the active priority of a
task do not affect the priority of the call, unless the base
priority of the task is set.
c. When the base priority of a task is set, see D.5, if the task is
blocked on an entry call, and the call is queued, the priority of
the call is updated to the new active priority of the calling task.
This causes the call to be removed from and then reinserted in the
queue at the new active priority.
d. When more than one condition of an entry_barrier of a protected
object becomes True, and more than one of the respective queues is
nonempty, the call with the highest priority is selected. If more
than one such call has the same priority, the call that is queued on
the entry whose declaration is first in textual order in the
protected_definition is selected. For members of the same entry
family, the one with the lower family index is selected.
e. If the expiration time of two or more open delay_alternatives is the
same and no other accept_alternatives are open, the
sequence_of_statements of the delay_alternative that is first in
textual order in the selective_accept is executed.
f. When more than one alternative of a selective_accept is open and has
queued calls, an alternative whose queue has the highest-priority
call at its head is selected. If two or more open alternatives have
equal-priority queued calls, then a call on the entry in the
accept_alternative that is first in textual order in the
selective_accept is selected.
Implementation Permissions
1. Implementations are allowed to define other queuing policies, but need
not support more than one such policy per partition.
Implementation Advice
2. The implementation should use names that end with ``_Queuing'' for
implementation-defined queuing policies.
ΓòÉΓòÉΓòÉ 20.5. Dynamic Priorities ΓòÉΓòÉΓòÉ
1. This clause specifies how the base priority of a task can be modified or
queried at run time.
Static Semantics
2. The following language-defined library package exists:
3.
with System;
with Ada.Task_Identification; -- see C.7.1.
package Ada.Dynamic_Priorities is
4.
procedure Set_Priority
(Priority : in System.Any_Priority;
T : in Ada.Task_Identification.Task_ID :=
Ada.Task_Identification.Current_Task);
5.
function Get_Priority
(T : Ada.Task_Identification.Task_ID :=
Ada.Task_Identification.Current_Task)
return System.Any_Priority;
6.
end Ada.Dynamic_Priorities;
Dynamic Semantics
7. The procedure Set_Priority sets the base priority of the specified task
to the specified Priority value. Set_Priority has no effect if the task
is terminated.
8. The function Get_Priority returns T's current base priority.
Tasking_Error is raised if the task is terminated.
9. Program_Error is raised by Set_Priority and Get_Priority if T is equal to
Null_Task_ID.
10. Setting the task's base priority to the new value takes place as soon as
is practical but not while the task is performing a protected action.
This setting occurs no later then the next abort completion point of the
task T, see 9.8.
Bounded (Run-Time) Errors
11. If a task is blocked on a protected entry call, and the call is queued,
it is a bounded error to raise its base priority above the ceiling
priority of the corresponding protected object. When an entry call is
cancelled, it is a bounded error if the priority of the calling task is
higher than the ceiling priority of the corresponding protected object.
In either of these cases, either Program_Error is raised in the task that
called the entry, or its priority is temporarily lowered, or both, or
neither.
Erroneous Execution
12. If any subprogram in this package is called with a parameter T that
specifies a task object that no longer exists, the execution of the
program is erroneous.
Metrics
13. The implementation shall document the following metric:
a. The execution time of a call to Set_Priority, for the nonpreempting
case, in processor clock cycles. This is measured for a call that
modifies the priority of a ready task that is not running (which
cannot be the calling one), where the new base priority of the
affected task is lower than the active priority of the calling task,
and the affected task is not on any entry queue and is not executing
a protected operation.
NOTES
1. (22) Setting a task's base priority affects task dispatching. First, it
can change the task's active priority. Second, under the standard task
dispatching policy it always causes the task to move to the tail of the
ready queue corresponding to its active priority, even if the new base
priority is unchanged.
2. (23) Under the priority queuing policy, setting a task's base priority
has an effect on a queued entry call if the task is blocked waiting for
the call. That is, setting the base priority of a task causes the
priority of a queued entry call from that task to be updated and the call
to be removed and then reinserted in the entry queue at the new priority,
see D.4, unless the call originated from the triggering_statement of an
asynchronous_select.
3. (24) The effect of two or more Set_Priority calls executed in parallel on
the same task is defined as executing these calls in some serial order.
4. (25) The rule for when Tasking_Error is raised for Set_Priority or
Get_Priority is different from the rule for when Tasking_Error is raised
on an entry call, see 9.5.3. In particular, setting or querying the
priority of a completed or an abnormal task is allowed, so long as the
task is not yet terminated.
5. (26) Changing the priorities of a set of tasks can be performed by a
series of calls to Set_Priority for each task separately. For this to
work reliably, it should be done within a protected operation that has
high enough ceiling priority to guarantee that the operation completes
without being preempted by any of the affected tasks.
ΓòÉΓòÉΓòÉ 20.6. Preemptive Abort ΓòÉΓòÉΓòÉ
1. This clause specifies requirements on the immediacy with which an aborted
construct is completed.
Dynamic Semantics
2. On a system with a single processor, an aborted construct is completed
immediately at the first point that is outside the execution of an
abort-deferred operation.
Documentation Requirements
3. On a multiprocessor, the implementation shall document any conditions
that cause the completion of an aborted construct to be delayed later
than what is specified for a single processor.
Metrics
4. The implementation shall document the following metrics:
a. The execution time, in processor clock cycles, that it takes for an
abort_statement to cause the completion of the aborted task. This is
measured in a situation where a task T2 preempts task T1 and aborts
T1. T1 does not have any finalization code. T2 shall verify that T1
has terminated, by means of the Terminated attribute.
b. On a multiprocessor, an upper bound in seconds, on the time that the
completion of an aborted task can be delayed beyond the point that
it is required for a single processor.
c. An upper bound on the execution time of an asynchronous_select, in
processor clock cycles. This is measured between a point immediately
before a task T1 executes a protected operation Pr.Set that makes
the condition of an entry_barrier Pr.Wait true, and the point where
task T2 resumes execution immediately after an entry call to Pr.Wait
in an asynchronous_select. T1 preempts T2 while T2 is executing the
abortable part, and then blocks itself so that T2 can execute. The
execution time of T1 is measured separately, and subtracted.
d. An upper bound on the execution time of an asynchronous_select, in
the case that no asynchronous transfer of control takes place. This
is measured between a point immediately before a task executes the
asynchronous_select with a nonnull abortable part, and the point
where the task continues execution immediately after it. The
execution time of the abortable part is subtracted.
Implementation Advice
1. Even though the abort_statement is included in the list of potentially
blocking operations, see 9.5.1, it is recommended that this statement be
implemented in a way that never requires the task executing the
abort_statement to block.
2. On a multi-processor, the delay associated with aborting a task on
another processor should be bounded; the implementation should use
periodic polling, if necessary, to achieve this.
NOTES
3. (27) Abortion does not change the active or base priority of the aborted
task.
4. (28) Abortion cannot be more immediate than is allowed by the rules for
deferral of abortion during finalization and in protected actions.
ΓòÉΓòÉΓòÉ 20.7. Tasking Restrictions ΓòÉΓòÉΓòÉ
1. This clause defines restrictions that can be used with a pragma
Restrictions, see 13.12, to facilitate the construction of highly
efficient tasking run-time systems.
Static Semantics
2. The following restriction_identifiers are language defined:
3. No_Task_Hierarchy
All (nonenvironment) tasks depend directly on the environment
task of the partition.
4. No_Nested_Finalization
Objects with controlled parts and access types that designate
such objects shall be declared only at library level.
5. No_Abort_Statements
There are no abort_statements, and there are no calls on
Task_Identification.Abort_Task.
6. No_Terminate_Alternatives
There are no selective_accepts with terminate_alternatives.
7. No_Task_Allocators
There are no allocators for task types or types containing
task subcomponents.
8. No_Implicit_Heap_Allocations
There are no operations that implicitly require heap storage
allocation to be performed by the implementation. The
operations that implicitly require heap storage allocation
are implementation defined.
9. No_Dynamic_Priorities
There are no semantic dependences on the package
Dynamic_Priorities.
10. No_Asynchronous_Control
There are no semantic dependences on the package
Asynchronous_Task_Control.
11. The following restriction_parameter_identifiers are language defined:
12. Max_Select_Alternatives
Specifies the maximum number of alternatives in a
selective_accept.
13. Max_Task_Entries
Specifies the maximum number of entries per task. The bounds
of every entry family of a task unit shall be static, or
shall be defined by a discriminant of a subtype whose
corresponding bound is static. A value of zero indicates
that no rendezvous are possible.
14. Max_Protected_Entries
Specifies the maximum number of entries per protected type.
The bounds of every entry family of a protected unit shall be
static, or shall be defined by a discriminant of a subtype
whose corresponding bound is static.
Dynamic Semantics
15. If the following restrictions are violated, the behavior is
implementation defined. If an implementation chooses to detect such a
violation, Storage_Error should be raised.
16. The following restriction_parameter_identifiers are language defined:
17. Max_Storage_At_Blocking
Specifies the maximum portion (in storage elements) of a
task's Storage_Size that can be retained by a blocked task.
18. Max_Asynchronous_Select_Nesting
Specifies the maximum dynamic nesting level of
asynchronous_selects. A value of zero prevents the use of any
asynchronous_select.
19. Max_Tasks
Specifies the maximum number of task creations that may be
executed over the lifetime of a partition, not counting the
creation of the environment task.
20. It is implementation defined whether the use of pragma Restrictions
results in a reduction in executable program size, storage requirements,
or execution time. If possible, the implementation should provide
quantitative descriptions of such effects for each restriction.
Implementation Advice
21. When feasible, the implementation should take advantage of the specified
restrictions to produce a more efficient implementation.
NOTES
22. (29) The above Storage_Checks can be suppressed with pragma Suppress.
ΓòÉΓòÉΓòÉ 20.8. Monotonic Time ΓòÉΓòÉΓòÉ
1. This clause specifies a high-resolution, monotonic clock package.
Static Semantics
2. The following language-defined library package exists:
3.
package Ada.Real_Time is
4.
type Time is private;
Time_First : constant Time;
Time_Last : constant Time;
Time_Unit : constant := implementation-defined-real-number;
1.
type Time_Span is private;
Time_Span_First : constant Time_Span;
Time_Span_Last : constant Time_Span;
Time_Span_Zero : constant Time_Span;
Time_Span_Unit : constant Time_Span;
2.
Tick : constant Time_Span;
function Clock return Time;
3.
function "+" (Left : Time; Right : Time_Span) return Time;
function "+" (Left : Time_Span; Right : Time) return Time;
function "-" (Left : Time; Right : Time_Span) return Time;
function "-" (Left : Time; Right : Time) return Time_Span;
4.
function "<" (Left, Right : Time) return Boolean;
function "<="(Left, Right : Time) return Boolean;
function ">" (Left, Right : Time) return Boolean;
function ">="(Left, Right : Time) return Boolean;
5.
function "+" (Left, Right : Time_Span) return Time_Span;
function "-" (Left, Right : Time_Span) return Time_Span;
function "-" (Right : Time_Span) return Time_Span;
function "*" (Left : Time_Span; Right : Integer) return Time_Span;
function "*" (Left : Integer; Right : Time_Span) return Time_Span;
function "/" (Left, Right : Time_Span) return Integer;
function "/" (Left : Time_Span; Right : Integer) return Time_Span;
6.
function "abs"(Right : Time_Span) return Time_Span;
7.
function "<" (Left, Right : Time_Span) return Boolean;
function "<="(Left, Right : Time_Span) return Boolean;
function ">" (Left, Right : Time_Span) return Boolean;
function ">="(Left, Right : Time_Span) return Boolean;
8.
function To_Duration (TS : Time_Span) return Duration;
function To_Time_Span (D : Duration) return Time_Span;
9.
function Nanoseconds (NS : Integer) return Time_Span;
function Microseconds (US : Integer) return Time_Span;
function Milliseconds (MS : Integer) return Time_Span;
10.
type Seconds_Count is range implementation-defined;
11.
procedure Split(T : in Time;
SC : out Seconds_Count;
TS : out Time_Span);
function Time_Of(SC : Seconds_Count; TS : Time_Span) return Time;
12.
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Real_Time;
13. In this Annex, real time is defined to be the physical time as observed
in the external environment. The type Time is a time type as defined by
9.6, values of this type may be used in a delay_until_statement. Values
of this type represent segments of an ideal time line. The set of values
of the type Time corresponds one-to-one with an implementation-defined
range of mathematical integers.
14. The Time value I represents the half-open real time interval that starts
with E+I*Time_Unit and is limited by E+(I+1)*Time_Unit, where Time_Unit
is an implementation-defined real number and E is an unspecified origin
point, the epoch, that is the same for all values of the type Time. It is
not specified by the language whether the time values are synchronized
with any standard time reference. For example, E can correspond to the
time of system initialization or it can correspond to the epoch of some
time standard.
15. Values of the type Time_Span represent length of real time duration. The
set of values of this type corresponds one-to-one with an
implementation-defined range of mathematical integers. The Time_Span
value corresponding to the integer I represents the real-time duration
I*Time_Unit.
16. Time_First and Time_Last are the smallest and largest values of the Time
type, respectively. Similarly, Time_Span_First and Time_Span_Last are the
smallest and largest values of the Time_Span type, respectively.
17. A value of type Seconds_Count represents an elapsed time, measured in
seconds, since the epoch.
Dynamic Semantics
18. Time_Unit is the smallest amount of real time representable by the Time
type; it is expressed in seconds. Time_Span_Unit is the difference
between two successive values of the Time type. It is also the smallest
positive value of type Time_Span. Time_Unit and Time_Span_Unit represent
the same real time duration. A clock tick is a real time interval during
which the clock value (as observed by calling the Clock function) remains
constant. Tick is the average length of such intervals.
19. The function To_Duration converts the value TS to a value of type
Duration. Similarly, the function To_Time_Span converts the value D to a
value of type Time_Span. For both operations, the result is rounded to
the nearest exactly representable value (away from zero if exactly
halfway between two exactly representable values).
20. To_Duration(Time_Span_Zero) returns 0.0, and To_Time_Span(0.0) returns
Time_Span_Zero.
21. The functions Nanoseconds, Microseconds, and Milliseconds convert the
input parameter to a value of the type Time_Span. NS, US, and MS are
interpreted as a number of nanoseconds, microseconds, and milliseconds
respectively. The result is rounded to the nearest exactly representable
value (away from zero if exactly halfway between two exactly
representable values).
22. The effects of the operators on Time and Time_Span are as for the
operators defined for integer types.
23. The function Clock returns the amount of time since the epoch.
24. The effects of the Split and Time_Of operations are defined as follows,
treating values of type Time, Time_Span, and Seconds_Count as
mathematical integers. The effect of Split(T,SC,TS) is to set SC and TS
to values such that T*Time_Unit = SC*1.0 + TS*Time_Unit, and 0.0 <=
TS*Time_Unit < 1.0. The value returned by Time_Of(SC,TS) is the value T
such that T*Time_Unit = SC*1.0 + TS*Time_Unit.
Implementation Requirements
25. The range of Time values shall be sufficient to uniquely represent the
range of real times from program start-up to 50 years later. Tick shall
be no greater than 1 millisecond. Time_Unit shall be less than or equal
to 20 microseconds.
26. Time_Span_First shall be no greater than -3600 seconds, and
Time_Span_Last shall be no less than 3600 seconds.
27. A clock jump is the difference between two successive distinct values of
the clock (as observed by calling the Clock function). There shall be no
backward clock jumps.
Documentation Requirements
28. The implementation shall document the values of Time_First, Time_Last,
Time_Span_First, Time_Span_Last, Time_Span_Unit, and Tick.
29. The implementation shall document the properties of the underlying time
base used for the clock and for type Time, such as the range of values
supported and any relevant aspects of the underlying hardware or
operating system facilities used.
30. The implementation shall document whether or not there is any
synchronization with external time references, and if such
synchronization exists, the sources of synchronization information, the
frequency of synchronization, and the synchronization method applied.
31. The implementation shall document any aspects of the the external
environment that could interfere with the clock behavior as defined in
this clause.
Metrics
32. For the purpose of the metrics defined in this clause, real time is
defined to be the International Atomic Time (TAI).
33. The implementation shall document the following metrics:
a.
An upper bound on the real-time duration of a clock tick. This is
a value D such that if t1 and t2 are any real times such that t1 <
t2 and Clock = Clock then t2 - t1 <= D.
t1 t2
b. An upper bound on the size of a clock jump.
c. An upper bound on the drift rate of Clock with respect to real time.
This is a real number D such that
d.
E*(1-D) <= (Clock - Clock ) <= E*(1+D)
t+E t
provided that: Clock + E*(1+D) <= Time_Last.
t
e.
where Clock is the value of Clock at time t, and E is a real time
t
time duration not less than 24 hours. The value of E used for this
metric shall be reported.
f. An upper bound on the execution time of a call to the Clock
function, in processor clock cycles.
g. Upper bounds on the execution times of the operators of the types
Time and Time_Span, in processor clock cycles.
Implementation Permissions
1. Implementations targeted to machines with word size smaller than 32 bits
need not support the full range and granularity of the Time and Time_Span
types.
Implementation Advice
2. When appropriate, implementations should provide configuration mechanisms
to change the value of Tick.
3. It is recommended that Calendar.Clock and Real_Time.Clock be implemented
as transformations of the same time base.
4. It is recommended that the ``best'' time base which exists in the
underlying system be available to the application through Clock. ``Best''
may mean highest accuracy or largest range.
NOTES
5. (30) The rules in this clause do not imply that the implementation can
protect the user from operator or installation errors which could result
in the clock being set incorrectly.
6. (31) Time_Unit is the granularity of the Time type. In contrast, Tick
represents the granularity of Real_Time.Clock. There is no requirement
that these be the same.
ΓòÉΓòÉΓòÉ 20.9. Delay Accuracy ΓòÉΓòÉΓòÉ
1. This clause specifies performance requirements for the delay_statement.
The rules apply both to delay_relative_statement and to
delay_until_statement. Similarly, they apply equally to a simple
delay_statement and to one which appears in a delay_alternative.
Dynamic Semantics
2. The effect of the delay_statement for Real_Time.Time is defined in terms
of Real_Time.Clock:
a.
If C is a value of Clock read before a task executes a
1
delay_relative_statement with duration D, and C is a value of Clock
2
read after the task resumes execution following that delay_statement,
then C - C >= D.
2 1
b. If C is a value of Clock read after a task resumes execution
following a delay_until_statement with Real_Time.Time value T, then
C >= T.
1. A simple delay_statement with a negative or zero value for the expiration
time does not cause the calling task to be blocked; it is nevertheless a
potentially blocking operation, see 9.5.1.
2. When a delay_statement appears in a delay_alternative of a
timed_entry_call the selection of the entry call is attempted, regardless
of the specified expiration time. When a delay_statement appears in a
selective_accept_alternative, and a call is queued on one of the open
entries, the selection of that entry call proceeds, regardless of the
value of the delay expression.
Documentation Requirements
3. The implementation shall document the minimum value of the delay
expression of a delay_relative_statement that causes the task to actually
be blocked.
4. The implementation shall document the minimum difference between the
value of the delay expression of a delay_until_statement and the value of
Real_Time.Clock, that causes the task to actually be blocked.
Metrics
5. The implementation shall document the following metrics:
a. An upper bound on the execution time, in processor clock cycles, of
a delay_relative_statement whose requested value of the delay
expression is less than or equal to zero.
b. An upper bound on the execution time, in processor clock cycles, of
a delay_until_statement whose requested value of the delay
expression is less than or equal to the value of Real_Time.Clock at
the time of executing the statement. Similarly, for Calendar.Clock.
c. An upper bound on the lateness of a delay_relative_statement, for a
positive value of the delay expression, in a situation where the
task has sufficient priority to preempt the processor as soon as it
becomes ready, and does not need to wait for any other execution
resources. The upper bound is expressed as a function of the value
of the delay expression. The lateness is obtained by subtracting the
value of the delay expression from the actual duration. The actual
duration is measured from a point immediately before a task executes
the delay_statement to a point immediately after the task resumes
execution following this statement.
d. An upper bound on the lateness of a delay_until_statement, in a
situation where the value of the requested expiration time is after
the time the task begins executing the statement, the task has
sufficient priority to preempt the processor as soon as it becomes
ready, and it does not need to wait for any other execution
resources. The upper bound is expressed as a function of the
difference between the requested expiration time and the clock value
at the time the statement begins execution. The lateness of a
delay_until_statement is obtained by subtracting the requested
expiration time from the real time that the task resumes execution
following this statement.
NOTES
1. (32) The execution time of a delay_statement that does not cause the task
to be blocked (e.g. ``delay 0.0;'' ) is of interest in situations where
delays are used to achieve voluntary round-robin task dispatching among
equal-priority tasks.
ΓòÉΓòÉΓòÉ 20.10. Synchronous Task Control ΓòÉΓòÉΓòÉ
1. This clause describes a language-defined private semaphore (suspension
object), which can be used for two-stage suspend operations and as a
simple building block for implementing higher-level queues.
Static Semantics
2. The following language-defined package exists:
3.
package Ada.Synchronous_Task_Control is
4.
type Suspension_Object is limited private;
procedure Set_True(S : in out Suspension_Object);
procedure Set_False(S : in out Suspension_Object);
function Current_State(S : Suspension_Object) return Boolean;
procedure Suspend_Until_True(S : in out Suspension_Object);
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Synchronous_Task_Control;
5. The type Suspension_Object is a by-reference type.
Dynamic Semantics
6. An object of the type Suspension_Object has two visible states: true and
false. Upon initialization, its value is set to false.
7. The operations Set_True and Set_False are atomic with respect to each
other and with respect to Suspend_Until_True; they set the state to true
and false respectively.
8. Current_State returns the current state of the object.
9. The procedure Suspend_Until_True blocks the calling task until the state
of the object S is true; at that point the task becomes ready and the
state of the object becomes false.
10. Program_Error is raised upon calling Suspend_Until_True if another task
is already waiting on that suspension object. Suspend_Until_True is a
potentially blocking operation, see 9.5.1.
Implementation Requirements
11. The implementation is required to allow the calling of Set_False and
Set_True during any protected action, even one that has its ceiling
priority in the Interrupt_Priority range.
ΓòÉΓòÉΓòÉ 20.11. Asynchronous Task Control ΓòÉΓòÉΓòÉ
1. This clause introduces a language-defined package to do asynchronous
suspend/resume on tasks. It uses a conceptual held priority value to
represent the task's held state.
Static Semantics
2. The following language-defined library package exists:
3.
with Ada.Task_Identification;
package Ada.Asynchronous_Task_Control is
procedure Hold(T : in Ada.Task_Identification.Task_ID);
procedure Continue(T : in Ada.Task_Identification.Task_ID);
function Is_Held(T : Ada.Task_Identification.Task_ID)
return Boolean;
end Ada.Asynchronous_Task_Control;
Dynamic Semantics
4. After the Hold operation has been applied to a task, the task becomes
held. For each processor there is a conceptual idle task, which is always
ready. The base priority of the idle task is below
System.Any_Priority'First. The held priority is a constant of the type
integer whose value is below the base priority of the idle task.
5. The Hold operation sets the state of T to held. For a held task: the
task's own base priority does not constitute an inheritance source (see
D.1) and the value of the held priority is defined to be such a source
instead.
6. The Continue operation resets the state of T to not-held; T's active
priority is then reevaluated as described in D.1. This time, T's base
priority is taken into account.
7. The Is_Held function returns True if and only if T is in the held state.
8. As part of these operations, a check is made that the task identified by
T is not terminated. Tasking_Error is raised if the check fails.
Program_Error is raised if the value of T is Null_Task_ID.
Erroneous Execution
9. If any operation in this package is called with a parameter T that
specifies a task object that no longer exists, the execution of the
program is erroneous.
Implementation Permissions
10. An implementation need not support Asynchronous_Task_Control if it is
infeasible to support it in the target environment.
NOTES
11. (33) It is a consequence of the priority rules that held tasks cannot be
dispatched on any processor in a partition (unless they are inheriting
priorities) since their priorities are defined to be below the priority
of any idle task.
12. (34) The effect of calling Get_Priority and Set_Priority on a Held task
is the same as on any other task.
13. (35) Calling Hold on a held task or Continue on a non-held task has no
effect.
14. (36) The rules affecting queuing are derived from the above rules, in
addition to the normal priority rules:
a. When a held task is on the ready queue, its priority is so low as to
never reach the top of the queue as long as there are other tasks on
that queue.
b. If a task is executing in a protected action, inside a rendezvous,
or is inheriting priorities from other sources (e.g. when
activated), it continues to execute until it is no longer executing
the corresponding construct.
c. If a task becomes held while waiting (as a caller) for a rendezvous
to complete, the active priority of the accepting task is not
affected.
d. If a task becomes held while waiting in a selective_accept, and a
entry call is issued to one of the open entries, the corresponding
accept body executes. When the rendezvous completes, the active
priority of the accepting task is lowered to the held priority
(unless it is still inheriting from other sources), and the task
does not execute until another Continue.
e. The same holds if the held task is the only task on a protected
entry queue whose barrier becomes open. The corresponding entry body
executes.
ΓòÉΓòÉΓòÉ 20.12. Other Optimizations and Determinism Rules ΓòÉΓòÉΓòÉ
1. This clause describes various requirements for improving the response and
determinism in a real-time system.
Implementation Requirements
2. If the implementation blocks interrupts, see C.3, not as a result of
direct user action (e.g. an execution of a protected action) there shall
be an upper bound on the duration of this blocking.
3. The implementation shall recognize entry-less protected types. The
overhead of acquiring the execution resource of an object of such a type,
see 9.5.1, shall be minimized. In particular, there should not be any
overhead due to evaluating entry_barrier conditions.
4. Unchecked_Deallocation shall be supported for terminated tasks that are
designated by access types, and shall have the effect of releasing all
the storage associated with the task. This includes any run-time system
or heap storage that has been implicitly allocated for the task by the
implementation.
Documentation Requirements
5. The implementation shall document the upper bound on the duration of
interrupt blocking caused by the implementation. If this is different for
different interrupts or interrupt priority levels, it should be
documented for each case.
Metrics
6. The implementation shall document the following metric:
a. The overhead associated with obtaining a mutual-exclusive access to
an entry-less protected object. This shall be measured in the
following way:
1. For a protected object of the form:
2.
protected Lock is
procedure Set;
function Read return Boolean;
private
Flag : Boolean := False;
end Lock;
3.
protected body Lock is
procedure Set is
begin
Flag := True;
end Set;
function Read return Boolean
Begin
return Flag;
end Read;
end Lock;
4. The execution time, in processor clock cycles, of a call to
Set. This shall be measured between the point just before
issuing the call, and the point just after the call completes.
The function Read shall be called later to verify that Set was
indeed called (and not optimized away). The calling task shall
have sufficiently high priority as to not be preempted during
the measurement period. The protected object shall have
sufficiently high ceiling priority to allow the task to call
Set.
5. For a multiprocessor, if supported, the metric shall be
reported for the case where no contention (on the execution
resource) exists from tasks executing on other processors.
ΓòÉΓòÉΓòÉ 21. Distributed Systems (normative) ΓòÉΓòÉΓòÉ
1. This Annex defines facilities for supporting the implementation of
distributed systems using multiple partitions working cooperatively as
part of a single Ada program.
Post-Compilation Rules
2. A distributed system is an interconnection of one or more processing
nodes (a system resource that has both computational and storage
capabilities), and zero or more storage nodes (a system resource that has
only storage capabilities, with the storage addressable by one or more
processing nodes).
3. A distributed program comprises one or more partitions that execute
independently (except when they communicate) in a distributed system.
4. The process of mapping the partitions of a program to the nodes in a
distributed system is called configuring the partitions of the program.
Implementation Requirements
5. The implementation shall provide means for explicitly assigning library
units to a partition and for the configuring and execution of a program
consisting of multiple partitions on a distributed system; the means are
implementation defined.
Implementation Permissions
6. An implementation may require that the set of processing nodes of a
distributed system be homogeneous.
NOTES
7. (1) The partitions comprising a program may be executed on differently
configured distributed systems or on a non-distributed system without
requiring recompilation. A distributed program may be partitioned
differently from the same set of library units without recompilation. The
resulting execution is semantically equivalent.
8. (2) A distributed program retains the same type safety as the equivalent
single partition program.
E.1 Partitions
E.2 Categorization of Library Units
E.3 Consistency of a Distributed System
E.4 Remote Subprogram Calls
E.5 Partition Communication Subsystem --- The
Detailed Node Listing ---
E.1 Partitions
E.2 Categorization of Library Units
E.2.1 Shared Passive Library Units
E.2.2 Remote Types Library Units
E.2.3 Remote Call Interface Library Units
E.3 Consistency of a Distributed System
E.4 Remote Subprogram Calls
E.4.1 Pragma Asynchronous
E.4.2 Example of Use of a Remote Access-to-Class-Wide
Type
E.5 Partition Communication Subsystem
ΓòÉΓòÉΓòÉ 21.1. Partitions ΓòÉΓòÉΓòÉ
1. The partitions of a distributed program are classified as either active
or passive.
Post-Compilation Rules
2. An active partition is a partition as defined in 10.2. A passive
partition is a partition that has no thread of control of its own, whose
library units are all preelaborated, and whose data and subprograms are
accessible to one or more active partitions.
3. A passive partition shall include only library_items that either are
declared pure or are shared passive, see 10.2.1, and E.2.1.
4. An active partition shall be configured on a processing node. A passive
partition shall be configured either on a storage node or on a processing
node.
5. The configuration of the partitions of a program onto a distributed
system shall be consistent with the possibility for data references or
calls between the partitions implied by their semantic dependences. Any
reference to data or call of a subprogram across partitions is called a
remote access.
Dynamic Semantics
6. A library_item is elaborated as part of the elaboration of each partition
that includes it. If a normal library unit, see E.2, has state, then a
separate copy of the state exists in each active partition that
elaborates it. The state evolves independently in each such partition.
7. An active partition terminates when its environment task terminates. A
partition becomes inaccessible if it terminates or if it is aborted. An
active partition is aborted when its environment task is aborted. In
addition, if a partition fails during its elaboration, it becomes
inaccessible to other partitions. Other implementation-defined events can
also result in a partition becoming inaccessible.
8. For a prefix D that denotes a library-level declaration, excepting a
declaration of or within a declared-pure library unit, the following
attribute is defined:
9. D'Partition_ID
Denotes a value of the type universal_integer that
identifies the partition in which D was elaborated. If D
denotes the declaration of a remote call interface
library unit, see E.2.3, the given partition is the
one where the body of D was elaborated.
Bounded (Run-Time) Errors
10. It is a bounded error for there to be cyclic elaboration dependences
between the active partitions of a single distributed program. The
possible effects are deadlock during elaboration, or the raising of
Program_Error in one or all of the active partitions involved.
Implementation Permissions
11. An implementation may allow multiple active or passive partitions to be
configured on a single processing node, and multiple passive partitions
to be configured on a single storage node. In these cases, the scheduling
policies, treatment of priorities, and management of shared resources
between these partitions are implementation defined.
12. An implementation may allow separate copies of an active partition to be
configured on different processing nodes, and to provide appropriate
interactions between the copies to present a consistent state of the
partition to other active partitions.
13. In an implementation, the partitions of a distributed program need not be
loaded and elaborated all at the same time; they may be loaded and
elaborated one at a time over an extended period of time. An
implementation may provide facilities to abort and reload a partition
during the execution of a distributed program.
14. An implementation may allow the state of some of the partitions of a
distributed program to persist while other partitions of the program
terminate and are later reinvoked.
NOTES
15. (3) Library units are grouped into partitions after compile time, but
before run time. At compile time, only the relevant library unit
properties are identified using categorization pragmas.
16. (4) The value returned by the Partition_ID attribute can be used as a
parameter to implementation-provided subprograms in order to query
information about the partition.
ΓòÉΓòÉΓòÉ 21.2. Categorization of Library Units ΓòÉΓòÉΓòÉ
1. Library units can be categorized according to the role they play in a
distributed program. Certain restrictions are associated with each
category to ensure that the semantics of a distributed program remain
close to the semantics for a nondistributed program.
2. A categorization pragma is a library unit pragma, see 10.1.5, that
restricts the declarations, child units, or semantic dependences of the
library unit to which it applies. A categorized library unit is a library
unit to which a categorization pragma applies.
3. The pragmas Shared_Passive, Remote_Types, and Remote_Call_Interface are
categorization pragmas. In addition, for the purposes of this Annex, the
pragma Pure, see 10.2.1 is considered a categorization pragma.
4. A library package or generic library package is called a shared passive
library unit if a Shared_Passive pragma applies to it. A library package
or generic library package is called a remote types library unit if a
Remote_Types pragma applies to it. A library package or generic library
package is called a remote call interface if a Remote_Call_Interface
pragma applies to it. A normal library unit is one to which no
categorization pragma applies.
5. The various categories of library units and the associated restrictions
are described in this clause and its subclauses. The categories are
related hierarchically in that the library units of one category can
depend semantically only on library units of that category or an earlier
one, except that the body of a remote types or remote call interface
library unit is unrestricted.
6. The overall hierarchy (including declared pure) is as follows:
7. Declared Pure
Can depend only on other declared pure library units;
8. Shared Passive
Can depend only on other shared passive or declared pure
library units;
9. Remote Types
The declaration of the library unit can depend only on other
remote types library units, or one of the above; the body of
the library unit is unrestricted;
10. Remote Call Interface
The declaration of the library unit can depend only on other
remote call interfaces, or one of the above; the body of the
library unit is unrestricted;
11. Normal
Unrestricted.
12. Declared pure and shared passive library units are preelaborated. The
declaration of a remote types or remote call interface library unit is
required to be preelaborable.
Implementation Requirements
13. For a given library-level type declared in a preelaborated library unit
or in the declaration of a remote types or remote call interface library
unit, the implementation shall choose the same representation for the
type upon each elaboration of the type's declaration for different
partitions of the same program.
Implementation Permissions
14. Implementations are allowed to define other categorization pragmas.
E.2.1 Shared Passive Library Units
E.2.2 Remote Types Library Units
E.2.3 Remote Call Interface Library Units
ΓòÉΓòÉΓòÉ 21.2.1. Shared Passive Library Units ΓòÉΓòÉΓòÉ
1. A shared passive library unit is used for managing global data shared
between active partitions. The restrictions on shared passive library
units prevent the data or tasks of one active partition from being
accessible to another active partition through references implicit in
objects declared in the shared passive library unit.
Syntax
2. The form of a pragma Shared_Passive is as follows:
3.
pragma Shared_Passive[(library_unit_name)];
Legality Rules
4. A shared passive library unit is a library unit to which a Shared_Passive
pragma applies. The following restrictions apply to such a library unit:
a. it shall be preelaborable, see 10.2.1,
b. it shall depend semantically only upon declared pure or shared
passive library units;
c. it shall not contain a library-level declaration of an access type
that designates a class-wide type, task type, or protected type with
entry_declarations; if the shared passive library unit is generic,
it shall not contain a declaration for such an access type unless
the declaration is nested within a body other than a package_body.
1. Notwithstanding the definition of accessibility given in 3.10.2, the
declaration of a library unit P1 is not accessible from within the
declarative region of a shared passive library unit P2, unless the shared
passive library unit P2 depends semantically on P1.
Static Semantics
2. A shared passive library unit is preelaborated.
Compilation Rules
3. A shared passive library unit shall be assigned to at most one partition
within a given program.
4. Notwithstanding the rule given in 10.2, a compilation unit in a given
partition does not need (in the sense of 10.2.) the shared passive
library units on which it depends semantically to be included in that
same partition; they will typically reside in separate passive
partitions.
ΓòÉΓòÉΓòÉ 21.2.2. Remote Types Library Units ΓòÉΓòÉΓòÉ
1. A remote types library unit supports the definition of types intended for
use in communication between active partitions.
Syntax
2. The form of a pragma Remote_Types is as follows:
3.
pragma Remote_Types[(library_unit_name)];
Legality Rules
4. A remote types library unit is a library unit to which the pragma
Remote_Types applies. The following restrictions apply to the declaration
of such a library unit:
a. it shall be preelaborable;
b. it shall depend semantically only on declared pure, shared passive,
or other remote types library units;
c. it shall not contain the declaration of any variable within the
visible part of the library unit;
d. if the full view of a type declared in the visible part of the
library unit has a part that is of a non-remote access type, then
that access type, or the type of some part that includes the access
type subcomponent, shall have user-specified Read and Write
attributes.
1. An access type declared in the visible part of a remote types or remote
call interface library unit is called a remote access type. Such a type
shall be either an access-to-subprogram type or a general access type
that designates a class-wide limited private type.
2. The following restrictions apply to the use of a remote
access-to-subprogram type:
a. A value of a remote access-to-subprogram type shall be converted
only to another (subtype-conformant) remote access-to-subprogram
type;
b. The prefix of an Access attribute_reference that yields a value of a
remote access-to-subprogram type shall statically denote a
(subtype-conformant) remote subprogram.
1. The following restrictions apply to the use of a remote
access-to-class-wide type:
a. The primitive subprograms of the corresponding specific limited
private type shall only have access parameters if they are
controlling formal parameters; the types of all the non-controlling
formal parameters shall have Read and Write attributes.
b. A value of a remote access-to-class-wide type shall be explicitly
converted only to another remote access-to-class-wide type;
c. A value of a remote access-to-class-wide type shall be dereferenced
(or implicitly converted to an anonymous access type) only as part
of a dispatching call where the value designates a controlling
operand of the call, see E.4: ``Remote Subprogram Calls'',
d. The Storage_Pool and Storage_Size attributes are not defined for
remote access-to-class-wide types; the expected type for an
allocator shall not be a remote access-to-class-wide type; a remote
access-to-class-wide type shall not be an actual parameter for a
generic formal access type;
NOTES
1. (5) A remote types library unit need not be pure, and the types it
defines may include levels of indirection implemented by using access
types. User-specified Read and Write attributes, see 13.13.2 provide for
sending values of such a type between active partitions, with Write
marshalling the representation, and Read unmarshalling any levels of
indirection.
ΓòÉΓòÉΓòÉ 21.2.3. Remote Call Interface Library Units ΓòÉΓòÉΓòÉ
1. A remote call interface library unit can be used as an interface for
remote procedure calls (RPCs) (or remote function calls) between active
partitions.
Syntax
2. The form of a pragma Remote_Call_Interface is as follows:
3.
pragma Remote_Call_Interface[(library_unit_name)];
4. The form of a pragma All_Calls_Remote is as follows:
5.
pragma All_Calls_Remote[(library_unit_name)];
a. A pragma All_Calls_Remote is a library unit pragma.
Legality Rules
1. A remote call interface (RCI) is a library unit to which the pragma
Remote_Call_Interface applies. A subprogram declared in the visible part
of such a library unit is called a remote subprogram.
2. The declaration of an RCI library unit shall be preelaborable (see
10.2.1) and shall depend semantically only upon declared pure, shared
passive, remote types, or other remote call interface library units.
3. In addition, the following restrictions apply to the visible part of an
RCI library unit:
a. it shall not contain the declaration of a variable;
b. it shall not contain the declaration of a limited type;
c. it shall not contain a nested generic_declaration;
d. it shall not contain the declaration of a subprogram to which a
pragma Inline applies;
e. it shall not contain a subprogram (or access-to-subprogram)
declaration whose profile has an access parameter, or a formal
parameter of a limited type unless that limited type has
user-specified Read and Write attributes;
f. any public child of the library unit shall be a remote call
interface library unit.
1. If a pragma All_Calls_Remote applies to a library unit, the library unit
shall be a remote call interface.
Post-Compilation Rules
2. A remote call interface library unit shall be assigned to at most one
partition of a given program. A remote call interface library unit whose
parent is also an RCI library unit shall be assigned only to the same
partition as its parent.
3. Notwithstanding the rule given in 10.2, a compilation unit in a given
partition that semantically depends on the declaration of an RCI library
unit, needs (in the sense of 10.2.) only the declaration of the RCI
library unit, not the body, to be included in that same partition.
Therefore, the body of an RCI library unit is included only in the
partition to which the RCI library unit is explicitly assigned.
Implementation Requirements
4. If a pragma All_Calls_Remote applies to a given RCI library package, then
the implementation shall route any call to a subprogram of the RCI
package from outside the declarative region of the package through the
Partition Communication Subsystem (PCS); see E.5. Calls to such
subprograms from within the declarative region of the package are defined
to be local and shall not go through the PCS.
Implementation Permissions
5. An implementation need not support the Remote_Call_Interface pragma nor
the All_Calls_Remote pragma. Explicit message-based communication between
active partitions can be supported as an alternative to RPC.
ΓòÉΓòÉΓòÉ 21.3. Consistency of a Distributed System ΓòÉΓòÉΓòÉ
1. This clause defines attributes and rules associated with verifying the
consistency of a distributed program.
Static Semantics
2. For a prefix P that statically denotes a program unit, the following
attributes are defined:
3. P'Version
Yields a value of the predefined type String that identifies
the version of the compilation unit that contains the
declaration of the program unit.
4. P'Body_Version
Yields a value of the predefined type String that identifies
the version of the compilation unit that contains the body
(but not any subunits) of the program unit.
5. The version of a compilation unit changes whenever the version changes
for any compilation unit on which it depends semantically. The version
also changes whenever the compilation unit itself changes in a
semantically significant way. It is implementation defined whether there
are other events (such as recompilation) that result in the version of a
compilation unit changing.
Bounded (Run-Time) Errors
6. In a distributed program, a library unit is consistent if the same
version of its declaration is used throughout. It is a bounded error to
elaborate a partition of a distributed program that contains a
compilation unit that depends on a different version of the declaration
of a shared passive or RCI library unit than that included in the
partition to which the shared passive or RCI library unit was assigned.
As a result of this error, Program_Error can be raised in one or both
partitions during elaboration; in any case, the partitions become
inaccessible to one another.
ΓòÉΓòÉΓòÉ 21.4. Remote Subprogram Calls ΓòÉΓòÉΓòÉ
1. A remote subprogram call is a subprogram call that invokes the execution
of a subprogram in another partition. The partition that originates the
remote subprogram call is the calling partition, and the partition that
executes the corresponding subprogram body is the called partition. Some
remote procedure calls are allowed to return prior to the completion of
subprogram execution. These are called asynchronous remote procedure
calls.
2. There are three different ways of performing a remote subprogram call:
a. As a direct call on a (remote) subprogram explicitly declared in a
remote call interface;
b. As an indirect call through a value of a remote access-to-subprogram
type;
c. As a dispatching call with a controlling operand designated by a
value of a remote access-to-class-wide type.
1. The first way of calling corresponds to a static binding between the
calling and the called partition. The latter two ways correspond to a
dynamic binding between the calling and the called partition.
2. A remote call interface library unit, see E.2.3, defines the remote
subprograms or remote access types used for remote subprogram calls.
Legality Rules
3. In a dispatching call with two or more controlling operands, if one
controlling operand is designated by a value of a remote
access-to-class-wide type, then all shall be.
Dynamic Semantics
4. For the execution of a remote subprogram call, subprogram parameters (and
later the results, if any) are passed using a stream-oriented
representation, see 13.13.1, which is suitable for transmission between
partitions. This action is called marshalling. Unmarshalling is the
reverse action of reconstructing the parameters or results from the
stream-oriented representation. Marshalling is performed initially as
part of the remote subprogram call in the calling partition;
unmarshalling is done in the called partition. After the remote
subprogram completes, marshalling is performed in the called partition,
and finally unmarshalling is done in the calling partition.
5. A calling stub is the sequence of code that replaces the subprogram body
of a remotely called subprogram in the calling partition. A receiving
stub is the sequence of code (the ``wrapper'') that receives a remote
subprogram call on the called partition and invokes the appropriate
subprogram body.
6. Remote subprogram calls are executed at most once, that is, if the
subprogram call returns normally, then the called subprogram's body was
executed exactly once.
7. The task executing a remote subprogram call blocks until the subprogram
in the called partition returns, unless the call is asynchronous. For an
asynchronous remote procedure call, the calling task can become ready
before the procedure in the called partition returns.
8. If a construct containing a remote call is aborted, the remote subprogram
call is cancelled. Whether the execution of the remote subprogram is
immediately aborted as a result of the cancellation is implementation
defined.
9. If a remote subprogram call is received by a called partition before the
partition has completed its elaboration, the call is kept pending until
the called partition completes its elaboration (unless the call is
cancelled by the calling partition prior to that).
10. If an exception is propagated by a remotely called subprogram, and the
call is not an asynchronous call, the corresponding exception is reraised
at the point of the remote subprogram call. For an asynchronous call, if
the remote procedure call returns prior to the completion of the remotely
called subprogram, any exception is lost.
11. The exception Communication_Error, see E.5 is raised if a remote call
cannot be completed due to difficulties in communicating with the called
partition.
12. All forms of remote subprogram calls are potentially blocking operations,
see 9.5.1.
13. In a remote subprogram call with a formal parameter of a class-wide type,
a check is made that the tag of the actual parameter identifies a tagged
type declared in a declared-pure or shared passive library unit, or in
the visible part of a remote types or remote call interface library unit.
Program_Error is raised if this check fails.
14. In a dispatching call with two or more controlling operands that are
designated by values of a remote access-to-class-wide type, a check is
made (in addition to the normal Tag_Check -- see 11.5.) that all the
remote access-to-class-wide values originated from Access
attribute_references that were evaluated by tasks of the same active
partition. Constraint_Error is raised if this check fails.
Implementation Requirements
15. The implementation of remote subprogram calls shall conform to the PCS
interface as defined by the specification of the language-defined package
System.RPC, see E.5. The calling stub shall use the Do_RPC procedure
unless the remote procedure call is asynchronous in which case Do_APC
shall be used. On the receiving side, the corresponding receiving stub
shall be invoked by the RPC-receiver.
NOTES
16. (6) A given active partition can both make and receive remote subprogram
calls. Thus, an active partition can act as both a client and a server.
17. (7) If a given exception is propagated by a remote subprogram call, but
the exception does not exist in the calling partition, the exception can
be handled by an others choice or be propagated to and handled by a third
partition.
E.4.1 Pragma Asynchronous
E.4.2 Example of Use of a Remote Access-to-Class-Wide
Type
ΓòÉΓòÉΓòÉ 21.4.1. Pragma Asynchronous ΓòÉΓòÉΓòÉ
1. This subclause introduces the pragma Asynchronous which allows a remote
subprogram call to return prior to completion of the execution of the
corresponding remote subprogram body.
Syntax
2. The form of a pragma Asynchronous is as follows:
3.
pragma Asynchronous(local_name);
Legality Rules
4. The local_name of a pragma Asynchronous shall denote either:
a. One or more remote procedures; the formal parameters of the
procedure(s) shall all be of mode in;
b. The first subtype of a remote access-to-procedure type; the formal
parameters of the designated profile of the type shall all be of
mode in;
c. The first subtype of a remote access-to-class-wide type.
Static Semantics
1. A pragma Asynchronous is a representation pragma. When applied to a type,
it specifies the type-related asynchronous aspect of the type.
Dynamic Semantics
2. A remote call is asynchronous if it is a call to a procedure, or a call
through a value of an access-to-procedure type, to which a pragma
Asynchronous applies. In addition, if a pragma Asynchronous applies to a
remote access-to-class-wide type, then a dispatching call on a procedure
with a controlling operand designated by a value of the type is
asynchronous if the formal parameters of the procedure are all of mode
in.
Implementation Requirements
3. Asynchronous remote procedure calls shall be implemented such that the
corresponding body executes at most once as a result of the call.
ΓòÉΓòÉΓòÉ 21.4.2. Example of Use of a Remote Access-to-Class-Wide Type ΓòÉΓòÉΓòÉ
Examples
1. Example of using a remote access-to-class-wide type to achieve dynamic
binding across active partitions:
2.
package Tapes is
pragma Pure(Tapes);
type Tape is abstract tagged limited private;
-- Primitive dispatching operations where
-- Tape is controlling operand
procedure Copy (From, To : access Tape;
Num_Recs : in Natural) is abstract;
procedure Rewind (T : access Tape) is abstract;
-- More operations
private
type Tape is ┬╖┬╖┬╖
end Tapes;
3.
with Tapes;
package Name_Server is
pragma Remote_Call_Interface;
-- Dynamic binding to remote operations is achieved
-- using the access-to-limited-class-wide type Tape_Ptr
type Tape_Ptr is access all Tapes.Tape'Class;
-- The following statically bound remote operations
-- allow for a name-server capability in this example
function Find (Name : String) return Tape_Ptr;
procedure Register (Name : in String; T : in Tape_Ptr);
procedure Remove (T : in Tape_Ptr);
-- More operations
end Name_Server;
4.
package Tape_Driver is
-- Declarations are not shown, they are irrelevant here
end Tape_Driver;
5.
with Tapes, Name_Server;
package body Tape_Driver is
type New_Tape is new Tapes.Tape with ┬╖┬╖┬╖
procedure Copy
(From, To : access New_Tape; Num_Recs: in Natural) is
begin
. . .
end Copy;
procedure Rewind (T : access New_Tape) is
begin
. . .
end Rewind;
-- Objects remotely accessible through use
-- of Name_Server operations
Tape1, Tape2 : aliased New_Tape;
begin
Name_Server.Register ("NINE-TRACK", Tape1'Access);
Name_Server.Register ("SEVEN-TRACK", Tape2'Access);
end Tape_Driver;
6.
with Tapes, Name_Server;
-- Tape_Driver is not needed
-- and thus not mentioned in the with_clause
procedure Tape_Client is
T1, T2 : Name_Server.Tape_Ptr;
begin
T1 := Name_Server.Find ("NINE-TRACK");
T2 := Name_Server.Find ("SEVEN-TRACK");
Tapes.Rewind (T1);
Tapes.Rewind (T2);
Tapes.Copy (T1, T2, 3);
end Tape_Client;
7. Notes on the example:
a. The package Tapes provides the necessary declarations of the type
and its primitive operations.
b. Name_Server is a remote call interface package and is elaborated in
a separate active partition to provide the necessary naming services
(such as Register and Find) to the entire distributed program
through remote subprogram calls.
c. Tape_Driver is a normal package that is elaborated in a partition
configured on the processing node that is connected to the tape
device(s). The abstract operations are overridden to support the
locally declared tape devices (Tape1, Tape2). The package is not
visible to its clients, but it exports the tape devices (as remote
objects) through the services of the Name_Server. This allows for
tape devices to be dynamically added, removed or replaced without
requiring the modification of the clients' code.
d. The Tape_Client procedure references only declarations in the Tapes
and Name_Server packages. Before using a tape for the first time, it
needs to query the Name_Server for a system-wide identity for that
tape. From then on, it can use that identity to access the tape
device.
e. Values of remote access type Tape_Ptr include the necessary
information to complete the remote dispatching operations that
result from dereferencing the controlling operands T1 and T2.
ΓòÉΓòÉΓòÉ 21.5. Partition Communication Subsystem ΓòÉΓòÉΓòÉ
1. The Partition Communication Subsystem (PCS) provides facilities for
supporting communication between the active partitions of a distributed
program. The package System.RPC is a language-defined interface to the
PCS. An implementation conforming to this Annex shall use the RPC
interface to implement remote subprogram calls.
Static Semantics
2. The following language-defined library package exists:
3.
with Ada.Streams; -- see 13.13.1.
package System.RPC is
4.
type Partition_ID is range 0 ┬╖┬╖ implementation-defined;
5.
Communication_Error : exception;
6.
type Params_Stream_Type(
Initial_Size : Ada.Streams.Stream_Element_Count) is new
Ada.Streams.Root_Stream_Type with private;
7.
procedure Read(
Stream : in out Params_Stream_Type;
Item : out Ada.Streams.Stream_Element_Array;
Last : out Ada.Streams.Stream_Element_Offset);
8.
procedure Write(
Stream : in out Params_Stream_Type;
Item : in Ada.Streams.Stream_Element_Array);
9.
-- Synchronous call
procedure Do_RPC(
Partition : in Partition_ID;
Params : access Params_Stream_Type;
Result : access Params_Stream_Type);
10.
-- Asynchronous call
procedure Do_APC(
Partition : in Partition_ID;
Params : access Params_Stream_Type);
11.
-- The handler for incoming RPCs
type RPC_Receiver is access procedure(
Params : access Params_Stream_Type;
Result : access Params_Stream_Type);
12.
procedure Establish_RPC_Receiver(
Partition : in Partition_ID;
Receiver : in RPC_Receiver);
13.
private
┬╖┬╖┬╖ -- not specified by the language
end System.RPC;
14. A value of the type Partition_ID is used to identify a partition.
15. An object of the type Params_Stream_Type is used for identifying the
particular remote subprogram that is being called, as well as marshalling
and unmarshalling the parameters or result of a remote subprogram call,
as part of sending them between partitions.
16. The Read and Write procedures override the corresponding abstract
operations for the type Params_Stream_Type.
Dynamic Semantics
17. The Do_RPC and Do_APC procedures send a message to the active partition
identified by the Partition parameter.
18. After sending the message, Do_RPC blocks the calling task until a reply
message comes back from the called partition or some error is detected by
the underlying communication system in which case Communication_Error is
raised at the point of the call to Do_RPC.
19. Do_APC operates in the same way as Do_RPC except that it is allowed to
return immediately after sending the message.
20. Upon normal return, the stream designated by the Result parameter of
Do_RPC contains the reply message.
21. The procedure System.RPC.Establish_RPC_Receiver is called once,
immediately after elaborating the library units of an active partition
(that is, right after the elaboration of the partition) if the partition
includes an RCI library unit, but prior to invoking the main subprogram,
if any. The Partition parameter is the Partition_ID of the active
partition being elaborated. The Receiver parameter designates an
implementation-provided procedure called the RPC-receiver which will
handle all RPCs received by the partition from the PCS.
Establish_RPC_Receiver saves a reference to the RPC-receiver; when a
message is received at the called partition, the RPC-receiver is called
with the Params stream containing the message. When the RPC-receiver
returns, the contents of the stream designated by Result is placed in a
message and sent back to the calling partition.
22. If a call on Do_RPC is aborted, a cancellation message is sent to the
called partition, to request that the execution of the remotely called
subprogram be aborted.
23. The subprograms declared in System.RPC are potentially blocking
operations.
Implementation Requirements
24. The implementation of the RPC-receiver shall be reentrant, thereby
allowing concurrent calls on it from the PCS to service concurrent remote
subprogram calls into the partition.
Documentation Requirements
25. The implementation of the PCS shall document whether the RPC-receiver is
invoked from concurrent tasks. If there is an upper limit on the number
of such tasks, this limit shall be documented as well, together with the
mechanisms to configure it (if this is supported).
Implementation Permissions
26. The PCS is allowed to contain implementation-defined interfaces for
explicit message passing, broadcasting, etc. Similarly, it is allowed to
provide additional interfaces to query the state of some remote partition
(given its partition ID) or of the PCS itself, to set timeouts and retry
parameters, to get more detailed error status, etc. These additional
interfaces should be provided in child packages of System.RPC.
27. A body for the package System.RPC need not be supplied by the
implementation.
Implementation Advice
28. Whenever possible, the PCS on the called partition should allow for
multiple tasks to call the RPC-receiver with different messages and
should allow them to block until the corresponding subprogram body
returns.
29. The Write operation on a stream of type Params_Stream_Type should raise
Storage_Error if it runs out of space trying to write the Item into the
stream.
NOTES
30. (8) The package System.RPC is not designed for direct calls by user
programs. It is instead designed for use in the implementation of remote
subprograms calls, being called by the calling stubs generated for a
remote call interface library unit to initiate a remote call, and in turn
calling back to an RPC-receiver that dispatches to the receiving stubs
generated for the body of a remote call interface, to handle a remote
call received from elsewhere.
ΓòÉΓòÉΓòÉ 22. Information Systems (normative) ΓòÉΓòÉΓòÉ
1. This Annex provides a set of facilities relevant to Information Systems
programming. These fall into several categories:
a. an attribute definition clause specifying Machine_Radix for a
decimal subtype;
b. the package Decimal, which declares a set of constants defining the
implementation's capacity for decimal types, and a generic procedure
for decimal division; and
c. the child packages Text_IO.Editing and Wide_Text_IO.Editing, which
support formatted and localized output of decimal data, based on
``picture String'' values.
1. See also: 3.5.9: ``Fixed Point Types'', 3.5.10: ``Operations of Fixed
Point Types'', 4.6: ``Type Conversions'', See 13.3: ``Representation
Attributes'', A.10.9: ``Input-Output for Real Types'', B.4: ``Interfacing
with COBOL'', B.3: ``Interfacing with C'', and G: ``Numerics''.
2. The character and string handling packages in A: ``Predefined Language
Environment'', are also relevant for Information Systems.
Implementation Advice
3. If COBOL (respectively, C) is widely supported in the target environment,
implementations supporting the Information Systems Annex should provide
the child package Interfaces.COBOL (respectively, Interfaces.C) specified
in Annex B and should support a convention_identifier of COBOL
(respectively, C) in the interfacing pragmas, see B, thus allowing Ada
programs to interface with programs written in that language.
F.1 Machine_Radix Attribute Definition Clause
F.2 The Package Decimal
F.3 Edited Output for Decimal Types --- The Detailed
Node Listing ---
F.1 Machine_Radix Attribute Definition Clause
F.2 The Package Decimal
F.3 Edited Output for Decimal Types
F.3.1 Picture String Formation
F.3.2 Edited Output Generation
F.3.3 The Package Text_IO.Editing
F.3.4 The Package Wide_Text_IO.Editing
ΓòÉΓòÉΓòÉ 22.1. Machine_Radix Attribute Definition Clause ΓòÉΓòÉΓòÉ
Static Semantics
1. Machine_Radix may be specified for a decimal first subtype (see 3.5.9)
via an attribute_definition_clause; the expression of such a clause shall
be static, and its value shall be 2 or 10. A value of 2 implies a binary
base range; a value of 10 implies a decimal base range.
Implementation Advice
2. Packed decimal should be used as the internal representation for objects
of subtype S when S'Machine_Radix = 10.
Examples
3. Example of Machine_Radix attribute definition clause:
4.
type Money is delta 0.01 digits 15;
for Money'Machine_Radix use 10;
ΓòÉΓòÉΓòÉ 22.2. The Package Decimal ΓòÉΓòÉΓòÉ
Static Semantics
1. The library package Decimal has the following declaration:
2.
package Ada.Decimal is
pragma Pure(Decimal);
3.
Max_Scale : constant := implementation-defined;
Min_Scale : constant := implementation-defined;
4.
Min_Delta : constant := 10.0**(-Max_Scale);
Max_Delta : constant := 10.0**(-Min_Scale);
5.
Max_Decimal_Digits : constant := implementation-defined;
6.
generic
type Dividend_Type is delta <> digits <>;
type Divisor_Type is delta <> digits <>;
type Quotient_Type is delta <> digits <>;
type Remainder_Type is delta <> digits <>;
procedure Divide (Dividend : in Dividend_Type;
Divisor : in Divisor_Type;
Quotient : out Quotient_Type;
Remainder : out Remainder_Type);
pragma Convention(Intrinsic, Divide);
7.
end Ada.Decimal;
8. Max_Scale is the largest N such that 10.0**(-N) is allowed as a decimal
type's delta. Its type is universal_integer.
9. Min_Scale is the smallest N such that 10.0**(-N) is allowed as a decimal
type's delta. Its type is universal_integer.
10. Min_Delta is the smallest value allowed for delta in a
decimal_fixed_point_definition. Its type is universal_real.
11. Max_Delta is the largest value allowed for delta in a
decimal_fixed_point_definition. Its type is universal_real.
12. Max_Decimal_Digits is the largest value allowed for digits in a
decimal_fixed_point_definition. Its type is universal_integer.
Static Semantics
13. The effect of Divide is as follows. The value of Quotient is
Quotient_Type(Dividend/Divisor). The value of Remainder is
Remainder_Type(Intermediate), where Intermediate is the difference
between Dividend and the product of Divisor and Quotient; this result is
computed exactly.
Implementation Requirements
14. Decimal.Max_Decimal_Digits shall be at least 18.
15. Decimal.Max_Scale shall be at least 18.
16. Decimal.Min_Scale shall be at most 0.
NOTES
17. (1) The effect of division yielding a quotient with control over rounding
versus truncation is obtained by applying either the function attribute
Quotient_Type'Round or the conversion Quotient_Type to the expression
Dividend/Divisor.
ΓòÉΓòÉΓòÉ 22.3. Edited Output for Decimal Types ΓòÉΓòÉΓòÉ
1. The child packages Text_IO.Editing and Wide_Text_IO.Editing provide
localizable formatted text output, known as edited output , for decimal
types. An edited output string is a function of a numeric value,
program-specifiable locale elements, and a format control value. The
numeric value is of some decimal type. The locale elements are:
a. the currency string;
b. the digits group separator character;
c. the radix mark character; and
d. the fill character that replaces leading zeros of the numeric value.
1. For Text_IO.Editing the edited output and currency strings are of type
String, and the locale characters are of type Character. For
Wide_Text_IO.Editing their types are Wide_String and Wide_Character,
respectively.
2. Each of the locale elements has a default value that can be replaced or
explicitly overridden.
3. A format-control value is of the private type Picture; it determines the
composition of the edited output string and controls the form and
placement of the sign, the position of the locale elements and the
decimal digits, the presence or absence of a radix mark, suppression of
leading zeros, and insertion of particular character values.
4. A Picture object is composed from a String value, known as a picture
String, that serves as a template for the edited output string, and a
Boolean value that controls whether a string of all space characters is
produced when the number's value is zero. A picture String comprises a
sequence of one- or two-Character symbols, each serving as a placeholder
for a character or string at a corresponding position in the edited
output string. The picture String symbols fall into several categories
based on their effect on the edited output string:
5.
Decimal Digit: '9'
Radix Control: '.' 'V'
Sign Control: '+' '-' '<' '>' "CR" "DB"
Currency Control: '$' '#'
Zero Suppression: 'Z' '*'
Simple Insertion: '_' 'B' '0' '/'
6. The entries are not case-sensitive. Mixed- or lower-case forms for "CR"
and "DB", and lower-case forms for 'V', 'Z', and 'B', have the same
effect as the upper-case symbols shown.
7. An occurrence of a '9' Character in the picture String represents a
decimal digit position in the edited output string.
8. A radix control Character in the picture String indicates the position of
the radix mark in the edited output string: an actual character position
for '.', or an assumed position for 'V'.
9. A sign control Character in the picture String affects the form of the
sign in the edited output string. The '<' and '>' Character values
indicate parentheses for negative values. A Character '+', '-', or '<'
appears either singly, signifying a fixed-position sign in the edited
output, or repeated, signifying a floating-position sign that is preceded
by zero or more space characters and that replaces a leading 0.
10. A currency control Character in the picture String indicates an
occurrence of the currency string in the edited output string. The '$'
Character represents the complete currency string; the '#' Character
represents one character of the currency string. A '$' Character appears
either singly, indicating a fixed-position currency string in the edited
output, or repeated, indicating a floating-position currency string that
occurs in place of a leading 0. A sequence of '#' Character values
indicates either a fixed- or floating-position currency string, depending
on context.
11. A zero suppression Character in the picture String allows a leading zero
to be replaced by either the space character (for 'Z') or the fill
character (for '*').
12. A simple insertion Character in the picture String represents, in
general, either itself (if '/' or '0'), the space character (if 'B'), or
the digits group separator character (if '_'). In some contexts it is
treated as part of a floating sign, floating currency, or zero
suppression string.
13. An example of a picture String is "<###Z_ZZ9.99>". If the currency string
is "FF", the separator character is ',', and the radix mark is '.' then
the edited output string values for the decimal values 32.10 and -5432.10
are "bbFFbbb32.10b" and "(bFF5,432.10)", respectively, where 'b'
indicates the space character.
14. The generic packages Text_IO.Decimal_IO and Wide_Text_IO.Decimal_IO (see
A.10.9: ``Input-Output for Real Types'') provide text input and
non-edited text output for decimal types.
NOTES
15. (2) A picture String is of type Standard.String, both for Text_IO.Editing
and Wide_Text_IO.Editing.
F.3.1 Picture String Formation
F.3.2 Edited Output Generation
F.3.3 The Package Text_IO.Editing
F.3.4 The Package Wide_Text_IO.Editing
ΓòÉΓòÉΓòÉ 22.3.1. Picture String Formation ΓòÉΓòÉΓòÉ
1. A well-formed picture String, or simply picture String, is a String value
that conforms to the syntactic rules, composition constraints, and
character replication conventions specified in this clause.
Dynamic Semantics
1.
picture_string ::=
fixed_$_picture_string
| fixed_#_picture_string
| floating_currency_picture_string
| non_currency_picture_string
2.
fixed_$_picture_string ::=
[fixed_LHS_sign] fixed_$_char {direct_insertion}
[zero_suppression] number [RHS_sign]
| [fixed_LHS_sign {direct_insertion}] [zero_suppression]
number fixed_$_char {direct_insertion} [RHS_sign]
| floating_LHS_sign number fixed_$_char {direct_insertion}
[RHS_sign]
| [fixed_LHS_sign] fixed_$_char {direct_insertion}
all_zero_suppression_number {direct_insertion} [RHS_sign]
| [fixed_LHS_sign {direct_insertion}] all_zero_suppression_number
{direct_insertion} fixed_$_char {direct_insertion}
[RHS_sign]
| all_sign_number {direct_insertion} fixed_$_char
{direct_insertion} [RHS_sign]
3.
fixed_#_picture_string ::=
[fixed_LHS_sign] single_#_currency {direct_insertion}
[zero_suppression] number [RHS_sign]
| [fixed_LHS_sign] multiple_#_currency {direct_insertion}
zero_suppression number [RHS_sign]
| [fixed_LHS_sign {direct_insertion}] [zero_suppression]
number fixed_#_currency {direct_insertion} [RHS_sign]
| floating_LHS_sign number fixed_#_currency {direct_insertion}
[RHS_sign]
| [fixed_LHS_sign] single_#_currency {direct_insertion}
all_zero_suppression_number {direct_insertion} [RHS_sign]
| [fixed_LHS_sign] multiple_#_currency {direct_insertion}
all_zero_suppression_number {direct_insertion} [RHS_sign]
| [fixed_LHS_sign {direct_insertion}] all_zero_suppression_number
{direct_insertion} fixed_#_currency {direct_insertion}
[RHS_sign]
| all_sign_number {direct_insertion} fixed_#_currency
{direct_insertion} [RHS_sign]
4.
floating_currency_picture_string ::=
[fixed_LHS_sign] {direct_insertion} floating_$_currency
number [RHS_sign]
| [fixed_LHS_sign] {direct_insertion} floating_#_currency
number [RHS_sign]
| [fixed_LHS_sign] {direct_insertion} all_currency_number
{direct_insertion} [RHS_sign]
5.
non_currency_picture_string ::=
[fixed_LHS_sign {direct_insertion}] zero_suppression
number [RHS_sign]
| [floating_LHS_sign]
number [RHS_sign]
| [fixed_LHS_sign {direct_insertion}]
all_zero_suppression_number {direct_insertion} [RHS_sign]
| all_sign_number {direct_insertion}
| fixed_LHS_sign direct_insertion {direct_insertion}
number [RHS_sign]
6.
fixed_LHS_sign ::= LHS_Sign
7.
LHS_Sign ::= + | - | <
8.
fixed_$_char ::= $
9.
direct_insertion ::= simple_insertion
10.
simple_insertion ::= _ | B | 0 | /
11.
zero_suppression ::= Z {Z
| context_sensitive_insertion}
| fill_string
12.
context_sensitive_insertion ::= simple_insertion
13.
fill_string ::= * {* | context_sensitive_insertion}
14.
number ::=
fore_digits [radix [aft_digits] {direct_insertion}]
| radix aft_digits {direct_insertion}
15.
fore_digits ::= 9 {9 | direct_insertion}
16.
aft_digits ::= {9 | direct_insertion} 9
17.
radix ::= . | V
18.
RHS_sign ::= + | - | > | CR | DB
19.
floating_LHS_sign ::=
LHS_Sign {context_sensitive_insertion} LHS_Sign
{LHS_Sign | context_sensitive_insertion}
20.
single_#_currency ::= #
21.
multiple_#_currency ::= ## {#}
22.
fixed_#_currency ::= single_#_currency | multiple_#_currency
23.
floating_$_currency ::=
$ {context_sensitive_insertion} $ {$
| context_sensitive_insertion}
24.
floating_#_currency ::=
# {context_sensitive_insertion} # {#
| context_sensitive_insertion}
25.
all_sign_number ::= all_sign_fore [radix [all_sign_aft]] [>]
26.
all_sign_fore ::=
sign_char {context_sensitive_insertion} sign_char {sign_char
| context_sensitive_insertion}
27.
all_sign_aft ::= {all_sign_aft_char} sign_char
all_sign_aft_char ::= sign_char | context_sensitive_insertion
28.
sign_char ::= + | - | <
29.
all_currency_number ::= all_currency_fore
[radix [all_currency_aft]]
30.
all_currency_fore ::=
currency_char {context_sensitive_insertion}
currency_char {currency_char | context_sensitive_insertion}
31.
all_currency_aft ::= {all_currency_aft_char} currency_char
all_currency_aft_char ::= currency_char
| context_sensitive_insertion
32.
currency_char ::= $ | #
33.
all_zero_suppression_number ::= all_zero_suppression_fore
[ radix [all_zero_suppression_aft]]
34.
all_zero_suppression_fore ::=
zero_suppression_char {zero_suppression_char
| context_sensitive_insertion}
35.
all_zero_suppression_aft ::= {all_zero_suppression_aft_char}
zero_suppression_char
all_zero_suppression_aft_char ::= zero_suppression_char
| context_sensitive_insertion
36.
zero_suppression_char ::= Z | *
37. The following composition constraints apply to a picture String:
a. A floating_LHS_sign does not have occurrences of different LHS_Sign
Character values.
b. If a picture String has '<' as fixed_LHS_sign, then it has '>' as
RHS_sign.
c. If a picture String has '<' in a floating_LHS_sign or in an
all_sign_number, then it has an occurrence of '>'.
d. If a picture String has '+' or '-' as fixed_LHS_sign, in a
floating_LHS_sign, or in an all_sign_number, then it has no
RHS_sign.
e. An instance of all_sign_number does not have occurrences of
different sign_char Character values.
f. An instance of all_currency_number does not have occurrences of
different currency_char Character values.
g. An instance of all_zero_suppression_number does not have occurrences
of different zero_suppression_char Character values, except for
possible case differences between 'Z' and 'z'.
1. A replicable Character is a Character that, by the above rules, can occur
in two consecutive positions in a picture String.
2. A Character replication is a String
3.
char & '(' & spaces & count_string & ')'
4. where char is a replicable Character, spaces is a String (possibly empty)
comprising only space Character values, and count_string is a String of
one or more decimal digit Character values. A Character replication in a
picture String has the same effect as (and is said to be equivalent to) a
String comprising n consecutive occurrences of char, where
n=Integer'Value(count_string).
5. An expanded picture String is a picture String containing no Character
replications.
NOTES
6. (3) Although a sign to the left of the number can float, a sign to the
right of the number is in a fixed position.
ΓòÉΓòÉΓòÉ 22.3.2. Edited Output Generation ΓòÉΓòÉΓòÉ
Dynamic Semantics
1. The contents of an edited output string are based on:
a. A value, Item, of some decimal type Num,
b. An expanded picture String Pic_String,
c. A Boolean value, Blank_When_Zero,
d. A Currency string,
e. A Fill character,
f. A Separator character, and
g. A Radix_Mark character.
1. The combination of a True value for Blank_When_Zero and a '*' character
in Pic_String is inconsistent; no edited output string is defined.
2. A layout error is identified in the rules below if leading non-zero
digits of Item, character values of the Currency string, or a negative
sign would be truncated; in such cases no edited output string is
defined.
3. The edited output string has lower bound 1 and upper bound N where N =
Pic_String'Length + Currency_Length_Adjustment - Radix_Adjustment, and
a. Currency_Length_Adjustment = Currency'Length - 1 if there is some
occurrence of '$' in Pic_String, and 0 otherwise.
b. Radix_Adjustment = 1 if there is an occurrence of 'V' or 'v' in
Pic_Str, and 0 otherwise.
c.
Let the magnitude of Item be expressed as a base-10 number
I ***I .F ***F , called the displayed magnitude of Item, where:
p 1 1 q
d. q = Min(Max(Num'Scale, 0), n) where n is 0 if Pic_String has no
radix and is otherwise the number of digit positions following radix
in Pic_String, where a digit position corresponds to an occurrence
of '9', a zero_suppression_char (for an
all_zero_suppression_number), a currency_char (for an
all_currency_number), or a sign_char (for an all_sign_number).
e.
I /= 0 if p>0.
p
1. If n < Num'Scale, then the above number is the result of rounding (away
from 0 if exactly midway between values).
2. If Blank_When_Zero = True and the displayed magnitude of Item is zero,
then the edited output string comprises all space character values.
Otherwise, the picture String is treated as a sequence of instances of
syntactic categories based on the rules in F.3.1, and the edited output
string is the concatenation of string values derived from these
categories according to the following mapping rules.
3. Table F-1 shows the mapping from a sign control symbol to a corresponding
character or string in the edited output. In the columns showing the
edited output, a lower-case 'b' represents the space character. If there
is no sign control symbol but the value of Item is negative, a layout
error occurs and no edited output string is produced.
+---------------------------------------------------+
| |
| Table F-1: Edited Output for Sign Control Symbols |
| |
+----------------+------------------+---------------+
| | | |
| Sign Control | Edited Output | Edited Output |
| Symbol | for Non-Negative | for Negative |
| | Number | Number |
| | | |
+----------------+------------------+---------------+
| | | |
| '+' | '+' | '-' |
| | | |
| '-' | 'b' | '-' |
| | | |
| '<' | 'b' | '(' |
| | | |
| '>' | 'b' | ')' |
| | | |
| "CR" | "bb" | "CR" |
| | | |
| "DB" | "bb" | "DB" |
| | | |
+----------------+------------------+---------------+
4. An instance of fixed_LHS_sign maps to a character as shown in Table F-1.
5. An instance of fixed_$_char maps to Currency.
6. An instance of direct_insertion maps to Separator if direct_insertion =
'_', and to the direct_insertion Character otherwise.
7. An instance of number maps to a string integer_part & radix_part &
fraction_part where:
a. The string for integer_part is obtained as follows:
1.
Occurrences of '9' in fore_digits of number are replaced
from right to left with the decimal digit character values
for I , ┬╖┬╖┬╖, I , respectively.
1 p
2. Each occurrence of '9' in fore_digits to the left of the
leftmost '9' replaced according to rule 1 is replaced with '0'.
3. If p exceeds the number of occurrences of '9' in fore_digits of
number, then the excess leftmost digits are eligible for use in
the mapping of an instance of zero_suppression,
floating_LHS_sign, floating_$_currency, or floating_#_currency
to the left of number; if there is no such instance, then a
layout error occurs and no edited output string is produced.
a. The radix_part is:
1. "" if number does not include a radix, if radix = 'V', or if
radix = 'v'
2. Radix_Mark if number includes '.' as radix
a. The string for fraction_part is obtained as follows:
1.
Occurrences of '9' in aft_digits of number are replaced
from left to right with the decimal digit character values
for F , ┬╖┬╖┬╖ F .
1 q
2. Each occurrence of '9' in aft_digits to the right of the
rightmost '9' replaced according to rule 1 is replaced by '0'.
1. An instance of zero_suppression maps to the string obtained as follows:
a. The rightmost 'Z', 'z', or '*' Character values are replaced with
the excess digits (if any) from the integer_part of the mapping of
the number to the right of the zero_suppression instance,
b. A context_sensitive_insertion Character is replaced as though it
were a direct_insertion Character, if it occurs to the right of some
'Z', 'z', or '*' in zero_suppression that has been mapped to an
excess digit,
c. Each Character to the left of the leftmost Character replaced
according to rule 1 above is replaced by:
1. the space character if the zero suppression Character is 'Z' or
'z', or
2. the Fill character if the zero suppression Character is '*'.
a. A layout error occurs if some excess digits remain after all 'Z',
'z', and '*' Character values in zero_suppression have been replaced
via rule 1; no edited output string is produced.
1. An instance of RHS_sign maps to a character or string as shown in Table
F-1.
2. An instance of floating_LHS_sign maps to the string obtained as follows.
a. Up to all but one of the rightmost LHS_Sign Character values are
replaced by the excess digits (if any) from the integer_part of the
mapping of the number to the right of the floating_LHS_sign
instance.
b. The next Character to the left is replaced with the character given
by the entry in Table F-1 corresponding to the LHS_Sign Character.
c. A context_sensitive_insertion Character is replaced as though it
were a direct_insertion Character, if it occurs to the right of the
leftmost LHS_Sign character replaced according to rule 1.
d. Any other Character is replaced by the space character┬╖┬╖
e. A layout error occurs if some excess digits remain after replacement
via rule 1; no edited output string is produced.
1. An instance of fixed_#_currency maps to the Currency string with n space
character values concatenated on the left (if the instance does not
follow a radix) or on the right (if the instance does follow a radix),
where n is the difference between the length of the fixed_#_currency
instance and Currency'Length. A layout error occurs if Currency'Length
exceeds the length of the fixed_#_currency instance; no edited output
string is produced.
2. An instance of floating_$_currency maps to the string obtained as
follows:
a. Up to all but one of the rightmost '$' Character values are replaced
with the excess digits (if any) from the integer_part of the mapping
of the number to the right of the floating_$_currency instance.
b. The next Character to the left is replaced by the Currency string.
c. A context_sensitive_insertion Character is replaced as though it
were a direct_insertion Character, if it occurs to the right of the
leftmost '$' Character replaced via rule 1.
d. Each other Character is replaced by the space character.
e. A layout error occurs if some excess digits remain after replacement
by rule 1; no edited output string is produced.
1. An instance of floating_#_currency maps to the string obtained as
follows:
a. Up to all but one of the rightmost '#' Character values are replaced
with the excess digits (if any) from the integer_part of the mapping
of the number to the right of the floating_#_currency instance.
b. The substring whose last Character occurs at the position
immediately preceding the leftmost Character replaced via rule 1,
and whose length is Currency'Length, is replaced by the Currency
string.
c. A context_sensitive_insertion Character is replaced as though it
were a direct_insertion Character, if it occurs to the right of the
leftmost '#' replaced via rule 1.
d. Any other Character is replaced by the space character.
e. A layout error occurs if some excess digits remain after replacement
rule 1, or if there is no substring with the required length for
replacement rule 2; no edited output string is produced.
1. An instance of all_zero_suppression_number maps to:
a. a string of all spaces if the displayed magnitude of Item is zero,
the zero_suppression_char is 'Z' or 'z', and the instance of
all_zero_suppression_number does not have a radix at its last
character position;
b. a string containing the Fill character in each position except for
the character (if any) corresponding to radix, if
zero_suppression_char = '*' and the displayed magnitude of Item is
zero;
c. otherwise, the same result as if each zero_suppression_char in
all_zero_suppression_aft were '9', interpreting the instance of
all_zero_suppression_number as either zero_suppression number (if a
radix and all_zero_suppression_aft are present), or as
zero_suppression otherwise.
1. An instance of all_sign_number maps to:
a. a string of all spaces if the displayed magnitude of Item is zero
and the instance of all_sign_number does not have a radix at its
last character position;
b. otherwise, the same result as if each sign_char in
all_sign_number_aft were '9', interpreting the instance of
all_sign_number as either floating_LHS_sign number (if a radix and
all_sign_number_aft are present), or as floating_LHS_sign otherwise.
1. An instance of all_currency_number maps to:
a. a string of all spaces if the displayed magnitude of Item is zero
and the instance of all_currency_number does not have a radix at its
last character position;
b. otherwise, the same result as if each currency_char in
all_currency_number_aft were '9', interpreting the instance of
all_currency_number as floating_$_currency number or
floating_#_currency number (if a radix and all_currency_number_aft
are present), or as floating_$_currency or floating_#_currency
otherwise.
Examples
1. In the result string values shown below, 'b' represents the space
character.
2.
Item: Picture and Result Strings:
3.
123456.78 Picture: "-###**_***_**9.99"
"bbb$***123,456.78"
"bbFF***123.456,78" (currency = "FF",
separator = '.',
radix mark = ',')
4.
123456.78 Picture: "-$$$**_***_**9.99"
Result: "bbb$***123,456.78"
"bbbFF***123.456,78" (currency = "FF",
separator = '.',
radix mark = ',')
5.
0.0 Picture: "-$$$$$$.$$"
Result: "bbbbbbbbbb"
6.
0.20 Picture: "-$$$$$$.$$"
Result: "bbbbbb$.20"
7.
-1234.565 Picture: "<<<<_<<<.<<###>"
Result: "bb(1,234.57DMb)" (currency = "DM")
8.
12345.67 Picture: "###_###_##9.99"
Result: "bbCHF12,345.67" (currency = "CHF")
ΓòÉΓòÉΓòÉ 22.3.3. The Package Text_IO.Editing ΓòÉΓòÉΓòÉ
1. The package Text_IO.Editing provides a private type Picture with
associated operations, and a generic package Decimal_Output. An object of
type Picture is composed from a well-formed picture String (see F.3.1)
and a Boolean item indicating whether a zero numeric value will result in
an edited output string of all space characters. The package
Decimal_Output contains edited output subprograms implementing the
effects defined in F.3.2.
Static Semantics
2. The library package Text_IO.Editing has the following declaration:
3.
package Ada.Text_IO.Editing is
4.
type Picture is private;
5.
function Valid (Pic_String : in String;
Blank_When_Zero : in Boolean := False)
return Boolean;
6.
function To_Picture (Pic_String : in String;
Blank_When_Zero : in Boolean := False)
return Picture;
7.
function Pic_String (Pic : in Picture) return String;
function Blank_When_Zero (Pic : in Picture) return Boolean;
8.
Max_Picture_Length : constant := implementation_defined;
9.
Picture_Error : exception;
10.
Default_Currency : constant String := "$";
Default_Fill : constant Character := '*';
Default_Separator : constant Character := ',';
Default_Radix_Mark : constant Character := '.';
11.
generic
type Num is delta <> digits <>;
Default_Currency : in String
:= Text_IO.Editing.Default_Currency;
Default_Fill : in Character
:= Text_IO.Editing.Default_Fill;
Default_Separator : in Character
:= Text_IO.Editing.Default_Separator;
Default_Radix_Mark : in Character
:= Text_IO.Editing.Default_Radix_Mark;
package Decimal_Output is
function Length (Pic : in Picture;
Currency : in String := Default_Currency)
return Natural;
12.
function Valid (Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency)
return Boolean;
13.
function Image
(Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark)
return String;
14.
procedure Put
(File : in File_Type;
Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark);
15.
procedure Put
(Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark);
16.
procedure Put
(To : out String;
Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark);
end Decimal_Output;
private
┬╖┬╖┬╖ -- not specified by the language
end Ada.Text_IO.Editing;
17. The exception Constraint_Error is raised if the Image function or any of
the Put procedures is invoked with a null string for Currency.
18.
function Valid (Pic_String : in String;
Blank_When_Zero : in Boolean := False)
return Boolean;
a. Valid returns True if Pic_String is a well-formed picture String
(see F.3.1) the length of whose expansion does not exceed
Max_Picture_Length, and if either Blank_When_Zero is False or
Pic_String contains no '*'.
1.
function To_Picture (Pic_String : in String;
Blank_When_Zero : in Boolean := False)
return Picture;
a. To_Picture returns a result Picture such that the application of the
function Pic_String to this result yields an expanded picture String
equivalent to Pic_String, and such that Blank_When_Zero applied to
the result Picture is the same value as the parameter
Blank_When_Zero. Picture_Error is raised if not Valid(Pic_String,
Blank_When_Zero).
1.
function Pic_String (Pic : in Picture) return String;
function Blank_When_Zero (Pic : in Picture) return Boolean;
a. If Pic is To_Picture(String_Item, Boolean_Item) for some String_Item
and Boolean_Item, then:
1. Pic_String(Pic) returns an expanded picture String equivalent
to String_Item and with any lower-case letter replaced with its
corresponding upper-case form, and
2. Blank_When_Zero(Pic) returns Boolean_Item.
a. If Pic_1 and Pic_2 are objects of type Picture, then "="(Pic_1,
Pic_2) is True when
1. Pic_String(Pic_1) = Pic_String(Pic_2), and
2. Blank_When_Zero(Pic_1) = Blank_When_Zero(Pic_2).
1.
function Length (Pic : in Picture;
Currency : in String := Default_Currency)
return Natural;
a. Length returns Pic_String(Pic)'Length + Currency_Length_Adjustment -
Radix_Adjustment where
1. Currency_Length_Adjustment =
a. Currency'Length - 1 if there is some occurrence of '$' in
Pic_String(Pic), and
b. 0 otherwise.
1. Radix_Adjustment =
a. 1 if there is an occurrence of 'V' or 'v' in Pic_Str(Pic),
and
b. 0 otherwise.
1.
function Valid (Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency)
return Boolean;
a. Valid returns True if Image(Item, Pic, Currency) does not raise
Layout_Error, and returns False otherwise.
1.
function Image (Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark)
return String;
a. Image returns the edited output String as defined in F.3.2, for
Item, Pic_String(Pic), Blank_When_Zero(Pic), Currency, Fill,
Separator, and Radix_Mark. If these rules identify a layout error,
then Image raises the exception Layout_Error.
1.
procedure Put (File : in File_Type;
Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark);
procedure Put (Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark);
a. Each of these Put procedures outputs Image(Item, Pic, Currency,
Fill, Separator, Radix_Mark) consistent with the conventions for Put
for other real types in case of bounded line length, see A.10.6:
``Get and Put Procedures''.
1.
procedure Put (To : out String;
Item : in Num;
Pic : in Picture;
Currency : in String := Default_Currency;
Fill : in Character := Default_Fill;
Separator : in Character := Default_Separator;
Radix_Mark : in Character := Default_Radix_Mark);
a. Put copies Image(Item, Pic, Currency, Fill, Separator, Radix_Mark)
to the given string, right justified. Otherwise unassigned Character
values in To are assigned the space character. If To'Length is less
than the length of the string resulting from Image, then
Layout_Error is raised.
Implementation Requirements
1. Max_Picture_Length shall be at least 30. The implementation shall support
currency strings of length up to at least 10, both for Default_Currency
in an instantiation of Decimal_Output, and for Currency in an invocation
of Image or any of the Put procedures.
NOTES
2. (4) The rules for edited output are based on COBOL (ANSI X3.23:1985,
endorsed by ISO as ISO 1989-1985), with the following differences:
a. The COBOL provisions for picture string localization and for 'P'
format are absent from Ada.
b. The following Ada facilities are not in COBOL:
1. currency symbol placement after the number,
2. localization of edited output string for multi-character
currency string values, including support for both
length-preserving and length-expanding currency symbols in
picture strings
3. localization of the radix mark, digits separator, and fill
character, and
4. parenthesization of negative values.
The value of 30 for Max_Picture_Length is the same limit as in COBOL.
ΓòÉΓòÉΓòÉ 22.3.4. The Package Wide_Text_IO.Editing ΓòÉΓòÉΓòÉ
Static Semantics
1. The child package Wide_Text_IO.Editing has the same contents as
Text_IO.Editing, except that:
a. each occurrence of Character is replaced by Wide_Character,
b. each occurrence of Text_IO is replaced by Wide_Text_IO,
c. the subtype of Default_Currency is Wide_String rather than String,
and
d. each occurrence of String in the generic package Decimal_Output is
replaced by Wide_String.
NOTES
1. (5) Each of the functions Wide_Text_IO.Editing.Valid, To_Picture, and
Pic_String has String (versus Wide_String) as its parameter or result
subtype, since a picture String is not localizable.
ΓòÉΓòÉΓòÉ 23. Numerics (normative) ΓòÉΓòÉΓòÉ
1. The Numerics Annex specifies
a. features for complex arithmetic, including complex I/O;
b. a mode (``strict mode''), in which the predefined arithmetic
operations of floating point and fixed point types and the functions
and operations of various predefined packages have to provide
guaranteed accuracy or conform to other numeric performance
requirements, which the Numerics Annex also specifies;
c. a mode (``relaxed mode''), in which no accuracy or other numeric
performance requirements need be satisfied, as for implementations
not conforming to the Numerics Annex;
d. models of floating point and fixed point arithmetic on which the
accuracy requirements of strict mode are based; and
e. the definitions of the model-oriented attributes of floating point
types that apply in the strict mode.
Implementation Advice
1. If Fortran (respectively, C) is widely supported in the target
environment, implementations supporting the Numerics Annex should provide
the child package Interfaces.Fortran (respectively, Interfaces.C)
specified in Annex B and should support a convention_identifier of
Fortran (respectively, C) in the interfacing pragmas, see B: ``Annex B'',
thus allowing Ada programs to interface with programs written in that
language.
G.1 Complex Arithmetic
G.2 Numeric Performance Requirements --- The
Detailed Node Listing ---
G.1 Complex Arithmetic
G.1.1 Complex Types
G.1.2 Complex Elementary Functions
G.1.3 Complex Input-Output
G.1.4 The Package Wide_Text_IO.Complex_IO
G.2 Numeric Performance Requirements
G.2.1 Model of Floating Point Arithmetic
G.2.2 Model-Oriented Attributes of Floating Point
Types
G.2.3 Model of Fixed Point Arithmetic
G.2.4 Accuracy Requirements for the Elementary
Functions
G.2.5 Performance Requirements for Random Number
Generation
G.2.6 Accuracy Requirements for Complex Arithmetic
ΓòÉΓòÉΓòÉ 23.1. Complex Arithmetic ΓòÉΓòÉΓòÉ
1. Types and arithmetic operations for complex arithmetic are provided in
Generic_Complex_Types, which is defined in G.1.1. Implementation-defined
approximations to the complex analogs of the mathematical functions known
as the ``elementary functions'' are provided by the subprograms in
Generic_Complex_Elementary_Functions, which is defined in G.1.2. Both of
these library units are generic children of the predefined package
Numerics, see A.5. Nongeneric equivalents of these generic packages for
each of the predefined floating point types are also provided as children
of Numerics.
G.1.1 Complex Types
G.1.2 Complex Elementary Functions
G.1.3 Complex Input-Output
G.1.4 The Package Wide_Text_IO.Complex_IO
ΓòÉΓòÉΓòÉ 23.1.1. Complex Types ΓòÉΓòÉΓòÉ
Static Semantics
1. The generic library package Numerics.Generic_Complex_Types has the
following declaration:
2.
generic
type Real is digits <>;
package Ada.Numerics.Generic_Complex_Types is
pragma Pure(Generic_Complex_Types);
3.
type Complex is
record
Re, Im : Real'Base;
end record;
4.
type Imaginary is private;
5.
i : constant Imaginary;
j : constant Imaginary;
6.
function Re (X : Complex) return Real'Base;
function Im (X : Complex) return Real'Base;
function Im (X : Imaginary) return Real'Base;
7.
procedure Set_Re (X : in out Complex;
Re : in Real'Base);
procedure Set_Im (X : in out Complex;
Im : in Real'Base);
procedure Set_Im (X : out Imaginary;
Im : in Real'Base);
8.
function Compose_From_Cartesian (Re, Im : Real'Base)
return Complex;
function Compose_From_Cartesian (Re : Real'Base)
return Complex;
function Compose_From_Cartesian (Im : Imaginary)
return Complex;
9.
function Modulus (X : Complex) return Real'Base;
function "abs" (Right : Complex) return Real'Base
renames Modulus;
10.
function Argument (X : Complex) return Real'Base;
function Argument (X : Complex;
Cycle : Real'Base) return Real'Base;
11.
function Compose_From_Polar
(Modulus, Argument : Real'Base)
return Complex;
function Compose_From_Polar
(Modulus, Argument, Cycle : Real'Base)
return Complex;
12.
function "+" (Right : Complex) return Complex;
function "-" (Right : Complex) return Complex;
function Conjugate (X : Complex) return Complex;
13.
function "+" (Left, Right : Complex) return Complex;
function "-" (Left, Right : Complex) return Complex;
function "*" (Left, Right : Complex) return Complex;
function "/" (Left, Right : Complex) return Complex;
14.
function "**" (Left : Complex; Right : Integer) return Complex;
15.
function "+" (Right : Imaginary) return Imaginary;
function "-" (Right : Imaginary) return Imaginary;
function Conjugate (X : Imaginary) return Imaginary
renames "-";
function "abs" (Right : Imaginary) return Real'Base;
16.
function "+" (Left, Right : Imaginary) return Imaginary;
function "-" (Left, Right : Imaginary) return Imaginary;
function "*" (Left, Right : Imaginary) return Real'Base;
function "/" (Left, Right : Imaginary) return Real'Base;
17.
function "**" (Left : Imaginary; Right : Integer) return Complex;
18.
function "<" (Left, Right : Imaginary) return Boolean;
function "<=" (Left, Right : Imaginary) return Boolean;
function ">" (Left, Right : Imaginary) return Boolean;
function ">=" (Left, Right : Imaginary) return Boolean;
19.
function "+" (Left : Complex;
Right : Real'Base) return Complex;
function "+" (Left : Real'Base;
Right : Complex) return Complex;
function "-" (Left : Complex;
Right : Real'Base) return Complex;
function "-" (Left : Real'Base;
Right : Complex) return Complex;
function "*" (Left : Complex;
Right : Real'Base) return Complex;
function "*" (Left : Real'Base;
Right : Complex) return Complex;
function "/" (Left : Complex;
Right : Real'Base) return Complex;
function "/" (Left : Real'Base;
Right : Complex) return Complex;
20.
function "+" (Left : Complex;
Right : Imaginary) return Complex;
function "+" (Left : Imaginary;
Right : Complex) return Complex;
function "-" (Left : Complex;
Right : Imaginary) return Complex;
function "-" (Left : Imaginary;
Right : Complex) return Complex;
function "*" (Left : Complex;
Right : Imaginary) return Complex;
function "*" (Left : Imaginary;
Right : Complex) return Complex;
function "/" (Left : Complex;
Right : Imaginary) return Complex;
function "/" (Left : Imaginary;
Right : Complex) return Complex;
21.
function "+" (Left : Imaginary;
Right : Real'Base) return Complex;
function "+" (Left : Real'Base;
Right : Imaginary) return Complex;
function "-" (Left : Imaginary;
Right : Real'Base) return Complex;
function "-" (Left : Real'Base;
Right : Imaginary) return Complex;
function "*" (Left : Imaginary;
Right : Real'Base) return Imaginary;
function "*" (Left : Real'Base;
Right : Imaginary) return Imaginary;
function "/" (Left : Imaginary;
Right : Real'Base) return Imaginary;
function "/" (Left : Real'Base;
Right : Imaginary) return Imaginary;
22.
private
23.
type Imaginary is new Real'Base;
i : constant Imaginary := 1.0;
j : constant Imaginary := 1.0;
24.
end Ada.Numerics.Generic_Complex_Types;
25. The library package Numerics.Complex_Types defines the same types,
constants, and subprograms as Numerics.Generic_Complex_Types, except that
the predefined type Float is systematically substituted for Real'Base
throughout. Nongeneric equivalents of Numerics.Generic_Complex_Types for
each of the other predefined floating point types are defined similarly,
with the names Numerics.Short_Complex_Types, Numerics.Long_Complex_Types,
etc.
26. Complex is a visible type with cartesian components.
27. Imaginary is a private type; its full type is derived from Real'Base.
28. The arithmetic operations and the Re, Im, Modulus, Argument, and
Conjugate functions have their usual mathematical meanings. When applied
to a parameter of pure-imaginary type, the ``imaginary-part'' function Im
yields the value of its parameter, as the corresponding real value. The
remaining subprograms have the following meanings:
a. The Set_Re and Set_Im procedures replace the designated component of
a complex parameter with the given real value; applied to a
parameter of pure-imaginary type, the Set_Im procedure replaces the
value of that parameter with the imaginary value corresponding to
the given real value.
b. The Compose_From_Cartesian function constructs a complex value from
the given real and imaginary components. If only one component is
given, the other component is implicitly zero.
c. The Compose_From_Polar function constructs a complex value from the
given modulus (radius) and argument (angle). When the value of the
parameter Modulus is positive (resp., negative), the result is the
complex value represented by the point in the complex plane lying at
a distance from the origin given by the absolute value of Modulus
and forming an angle measured counterclockwise from the positive
(resp., negative) real axis given by the value of the parameter
Argument.
1. When the Cycle parameter is specified, the result of the Argument
function and the parameter Argument of the Compose_From_Polar function
are measured in units such that a full cycle of revolution has the given
value; otherwise, they are measured in radians.
2. The computed results of the mathematically multivalued functions are
rendered single-valued by the following conventions, which are meant to
imply the principal branch:
a. The result of the Modulus function is nonnegative.
b. The result of the Argument function is in the quadrant containing
the point in the complex plane represented by the parameter X. This
may be any quadrant (I through IV); thus, the range of the Argument
function is approximately -Pi to Pi (-Cycle/2.0 to Cycle/2.0, if the
parameter Cycle is specified). When the point represented by the
parameter X lies on the negative real axis, the result approximates
1. Pi (resp., -Pi) when the sign of the imaginary component of X
is positive (resp., negative), if Real'Signed_Zeros is True;
2. Pi, if Real'Signed_Zeros is False.
a. Because a result lying on or near one of the axes may not be exactly
representable, the approximation inherent in computing the result
may place it in an adjacent quadrant, close to but on the wrong side
of the axis.
Dynamic Semantics
1. The exception Numerics.Argument_Error is raised by the Argument and
Compose_From_Polar functions with specified cycle, signaling a parameter
value outside the domain of the corresponding mathematical function, when
the value of the parameter Cycle is zero or negative.
2. The exception Constraint_Error is raised by the division operator when
the value of the right operand is zero, and by the exponentiation
operator when the value of the left operand is zero and the value of the
exponent is negative, provided that Real'Machine_Overflows is True; when
Real'Machine_Overflows is False, the result is unspecified.
Constraint_Error can also be raised when a finite result overflows (see
G.2.6).
Implementation Requirements
3. In the implementation of Numerics.Generic_Complex_Types, the range of
intermediate values allowed during the calculation of a final result
shall not be affected by any range constraint of the subtype Real.
4. In the following cases, evaluation of a complex arithmetic operation
shall yield the prescribed result, provided that the preceding rules do
not call for an exception to be raised:
a. The results of the Re, Im, and Compose_From_Cartesian functions are
exact.
b. The real (resp., imaginary) component of the result of a binary
addition operator that yields a result of complex type is exact when
either of its operands is of pure-imaginary (resp., real) type.
c. The real (resp., imaginary) component of the result of a binary
subtraction operator that yields a result of complex type is exact
when its right operand is of pure-imaginary (resp., real) type.
d. The real component of the result of the Conjugate function for the
complex type is exact.
e. When the point in the complex plane represented by the parameter X
lies on the nonnegative real axis, the Argument function yields a
result of zero.
f. When the value of the parameter Modulus is zero, the
Compose_From_Polar function yields a result of zero.
g. When the value of the parameter Argument is equal to a multiple of
the quarter cycle, the result of the Compose_From_Polar function
with specified cycle lies on one of the axes. In this case, one of
its components is zero, and the other has the magnitude of the
parameter Modulus.
h. Exponentiation by a zero exponent yields the value one.
Exponentiation by a unit exponent yields the value of the left
operand. Exponentiation of the value one yields the value one.
Exponentiation of the value zero yields the value zero, provided
that the exponent is nonzero. When the left operand is of
pure-imaginary type, one component of the result of the
exponentiation operator is zero.
1. When the result, or a result component, of any operator of
Numerics.Generic_Complex_Types has a mathematical definition in terms of
a single arithmetic or relational operation, that result or result
component exhibits the accuracy of the corresponding operation of the
type Real.
2. Other accuracy requirements for the Modulus, Argument, and
Compose_From_Polar functions, and accuracy requirements for the
multiplication of a pair of complex operands or for division by a complex
operand, all of which apply only in the strict mode, are given in G.2.6.
3. The sign of a zero result or zero result component yielded by a complex
arithmetic operation or function is implementation defined when
Real'Signed_Zeros is True.
Implementation Permissions
4. The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package for the appropriate predefined
type.
5. Implementations may obtain the result of exponentiation of a complex or
pure-imaginary operand by repeated complex multiplication, with arbitrary
association of the factors and with a possible final complex
reciprocation (when the exponent is negative). Implementations are also
permitted to obtain the result of exponentiation of a complex operand,
but not of a pure-imaginary operand, by converting the left operand to a
polar representation; exponentiating the modulus by the given exponent;
multiplying the argument by the given exponent, when the exponent is
positive, or dividing the argument by the absolute value of the given
exponent, when the exponent is negative; and reconverting to a cartesian
representation. Because of this implementation freedom, no accuracy
requirement is imposed on complex exponentiation (except for the
prescribed results given above, which apply regardless of the
implementation method chosen).
Implementation Advice
6. Because the usual mathematical meaning of multiplication of a complex
operand and a real operand is that of the scaling of both components of
the former by the latter, an implementation should not perform this
operation by first promoting the real operand to complex type and then
performing a full complex multiplication. In systems that, in the future,
support an Ada binding to IEC 559:1989, the latter technique will not
generate the required result when one of the components of the complex
operand is infinite. (Explicit multiplication of the infinite component
by the zero component obtained during promotion yields a NaN that
propagates into the final result.) Analogous advice applies in the case
of multiplication of a complex operand and a pure-imaginary operand, and
in the case of division of a complex operand by a real or pure-imaginary
operand.
7. Likewise, because the usual mathematical meaning of addition of a complex
operand and a real operand is that the imaginary operand remains
unchanged, an implementation should not perform this operation by first
promoting the real operand to complex type and then performing a full
complex addition. In implementations in which the Signed_Zeros attribute
of the component type is True (and which therefore conform to IEC
559:1989 in regard to the handling of the sign of zero in predefined
arithmetic operations), the latter technique will not generate the
required result when the imaginary component of the complex operand is a
negatively signed zero. (Explicit addition of the negative zero to the
zero obtained during promotion yields a positive zero.) Analogous advice
applies in the case of addition of a complex operand and a pure-imaginary
operand, and in the case of subtraction of a complex operand and a real
or pure-imaginary operand.
8. Implementations in which Real'Signed_Zeros is True should attempt to
provide a rational treatment of the signs of zero results and result
components. As one example, the result of the Argument function should
have the sign of the imaginary component of the parameter X when the
point represented by that parameter lies on the positive real axis; as
another, the sign of the imaginary component of the Compose_From_Polar
function should be the same as (resp., the opposite of) that of the
Argument parameter when that parameter has a value of zero and the
Modulus parameter has a nonnegative (resp., negative) value.
ΓòÉΓòÉΓòÉ 23.1.2. Complex Elementary Functions ΓòÉΓòÉΓòÉ
Static Semantics
1. The generic library package Numerics.Generic_Complex_Elementary_Functions
has the following declaration:
2.
with Ada.Numerics.Generic_Complex_Types;
generic
with package Complex_Types is new
Ada.Numerics.Generic_Complex_Types (<>);
use Complex_Types;
package Ada.Numerics.Generic_Complex_Elementary_Functions is
pragma Pure(Generic_Complex_Elementary_Functions);
3.
function Sqrt (X : Complex) return Complex;
function Log (X : Complex) return Complex;
function Exp (X : Complex) return Complex;
function Exp (X : Imaginary) return Complex;
function "**" (Left : Complex;
Right : Complex) return Complex;
function "**" (Left : Complex;
Right : Real'Base) return Complex;
function "**" (Left : Real'Base;
Right : Complex) return Complex;
4.
function Sin (X : Complex) return Complex;
function Cos (X : Complex) return Complex;
function Tan (X : Complex) return Complex;
function Cot (X : Complex) return Complex;
5.
function Arcsin (X : Complex) return Complex;
function Arccos (X : Complex) return Complex;
function Arctan (X : Complex) return Complex;
function Arccot (X : Complex) return Complex;
6.
function Sinh (X : Complex) return Complex;
function Cosh (X : Complex) return Complex;
function Tanh (X : Complex) return Complex;
function Coth (X : Complex) return Complex;
7.
function Arcsinh (X : Complex) return Complex;
function Arccosh (X : Complex) return Complex;
function Arctanh (X : Complex) return Complex;
function Arccoth (X : Complex) return Complex;
8.
end Ada.Numerics.Generic_Complex_Elementary_Functions;
9. The library package Numerics.Complex_Elementary_Functions defines the
same subprograms as Numerics.Generic_Complex_Elementary_Functions, except
that the predefined type Float is systematically substituted for
Real'Base, and the Complex and Imaginary types exported by
Numerics.Complex_Types are systematically substituted for Complex and
Imaginary, throughout. Nongeneric equivalents of
Numerics.Generic_Complex_Elementary_Functions corresponding to each of
the other predefined floating point types are defined similarly, with the
names Numerics.Short_Complex_Elementary_Functions,
Numerics.Long_Complex_Elementary_Functions, etc.
10. The overloading of the Exp function for the pure-imaginary type is
provided to give the user an alternate way to compose a complex value
from a given modulus and argument. In addition to Compose_From_Polar(Rho,
Theta), see G.1.1, the programmer may write Rho * Exp(i * Theta).
11. The imaginary (resp., real) component of the parameter X of the forward
hyperbolic (resp., trigonometric) functions and of the Exp function (and
the parameter X, itself, in the case of the overloading of the Exp
function for the pure-imaginary type) represents an angle measured in
radians, as does the imaginary (resp., real) component of the result of
the Log and inverse hyperbolic (resp., trigonometric) functions.
12. The functions have their usual mathematical meanings. However, the
arbitrariness inherent in the placement of branch cuts, across which some
of the complex elementary functions exhibit discontinuities, is
eliminated by the following conventions:
a. The imaginary component of the result of the Sqrt and Log functions
is discontinuous as the parameter X crosses the negative real axis.
b. The result of the exponentiation operator when the left operand is
of complex type is discontinuous as that operand crosses the
negative real axis.
c. The real (resp., imaginary) component of the result of the Arcsin
and Arccos (resp., Arctanh) functions is discontinuous as the
parameter X crosses the real axis to the left of -1.0 or the right
of 1.0.
d. The real (resp., imaginary) component of the result of the Arctan
(resp., Arcsinh) function is discontinuous as the parameter X
crosses the imaginary axis below -i or above i.
e. The real component of the result of the Arccot function is
discontinuous as the parameter X crosses the imaginary axis between
-i and i.
f. The imaginary component of the Arccosh function is discontinuous as
the parameter X crosses the real axis to the left of 1.0.
g. The imaginary component of the result of the Arccoth function is
discontinuous as the parameter X crosses the real axis between -1.0
and 1.0.
1. The computed results of the mathematically multivalued functions are
rendered single-valued by the following conventions, which are meant to
imply the principal branch:
a. The real component of the result of the Sqrt and Arccosh functions
is nonnegative.
b. The same convention applies to the imaginary component of the result
of the Log function as applies to the result of the natural-cycle
version of the Argument function of Numerics.Generic_Complex_Types
(see G.1.1).
c. The range of the real (resp., imaginary) component of the result of
the Arcsin and Arctan (resp., Arcsinh and Arctanh) functions is
approximately -Pi/2.0 to Pi/2.0.
d. The real (resp., imaginary) component of the result of the Arccos
and Arccot (resp., Arccoth) functions ranges from 0.0 to
approximately Pi.
e. The range of the imaginary component of the result of the Arccosh
function is approximately -Pi to Pi.
1. In addition, the exponentiation operator inherits the single-valuedness
of the Log function.
Dynamic Semantics
2. The exception Numerics.Argument_Error is raised by the exponentiation
operator, signaling a parameter value outside the domain of the
corresponding mathematical function, when the value of the left operand
is zero and the real component of the exponent (or the exponent itself,
when it is of real type) is zero.
3. The exception Constraint_Error is raised, signaling a pole of the
mathematical function (analogous to dividing by zero), in the following
cases, provided that Complex_Types.Real'Machine_Overflows is True:
a. by the Log, Cot, and Coth functions, when the value of the parameter
X is zero;
b. by the exponentiation operator, when the value of the left operand
is zero and the real component of the exponent (or the exponent
itself, when it is of real type) is negative;
c. by the Arctan and Arccot functions, when the value of the parameter
X is +/-i;
d. by the Arctanh and Arccoth functions, when the value of the
parameter X is +/-1.0.
1. Constraint_Error can also be raised when a finite result overflows (see
G.2.6) this may occur for parameter values sufficiently near poles, and,
in the case of some of the functions, for parameter values having
components of sufficiently large magnitude. When
Complex_Types.Real'Machine_Overflows is False, the result at poles is
unspecified.
Implementation Requirements
2. In the implementation of Numerics.Generic_Complex_Elementary_Functions,
the range of intermediate values allowed during the calculation of a
final result shall not be affected by any range constraint of the subtype
Complex_Types.Real.
3. In the following cases, evaluation of a complex elementary function shall
yield the prescribed result (or a result having the prescribed
component), provided that the preceding rules do not call for an
exception to be raised:
a. When the parameter X has the value zero, the Sqrt, Sin, Arcsin, Tan,
Arctan, Sinh, Arcsinh, Tanh, and Arctanh functions yield a result of
zero; the Exp, Cos, and Cosh functions yield a result of one; the
Arccos and Arccot functions yield a real result; and the Arccoth
function yields an imaginary result.
b. When the parameter X has the value one, the Sqrt function yields a
result of one; the Log, Arccos, and Arccosh functions yield a result
of zero; and the Arcsin function yields a real result.
c. When the parameter X has the value -1.0, the Sqrt function yields
the result
1. i (resp., -i), when the sign of the imaginary component of X is
positive (resp., negative), if Complex_Types.Real'Signed_Zeros
is True;
2. i, if Complex_Types.Real'Signed_Zeros is False;
a. the Log function yields an imaginary result; and the Arcsin and
Arccos functions yield a real result.
b. When the parameter X has the value +/-i, the Log function yields an
imaginary result.
c. Exponentiation by a zero exponent yields the value one.
Exponentiation by a unit exponent yields the value of the left
operand (as a complex value). Exponentiation of the value one yields
the value one. Exponentiation of the value zero yields the value
zero.
1. Other accuracy requirements for the complex elementary functions, which
apply only in the strict mode, are given in G.2.6.
2. The sign of a zero result or zero result component yielded by a complex
elementary function is implementation defined when
Complex_Types.Real'Signed_Zeros is True.
Implementation Permissions
3. The nongeneric equivalent packages may, but need not, be actual
instantiations of the generic package with the appropriate predefined
nongeneric equivalent of Numerics.Generic_Complex_Types; if they are,
then the latter shall have been obtained by actual instantiation of
Numerics.Generic_Complex_Types.
4. The exponentiation operator may be implemented in terms of the Exp and
Log functions. Because this implementation yields poor accuracy in some
parts of the domain, no accuracy requirement is imposed on complex
exponentiation.
5. The implementation of the Exp function of a complex parameter X is
allowed to raise the exception Constraint_Error, signaling overflow, when
the real component of X exceeds an unspecified threshold that is
approximately log (Complex_Types.Real'Safe_Last). This permission
recognizes the impracticality of avoiding overflow in the marginal case
that the exponential of the real component of X exceeds the safe range of
Complex_Types.Real but both components of the final result do not.
Similarly, the Sin and Cos (resp., Sinh and Cosh) functions are allowed
to raise the exception Constraint_Error, signaling overflow, when the
absolute value of the imaginary (resp., real) component of the parameter
X exceeds an unspecified threshold that is approximately log
(Complex_Types.Real'Safe_Last)+log (2.0). This permission recognizes the
impracticality of avoiding overflow in the marginal case that the
hyperbolic sine or cosine of the imaginary (resp., real) component of X
exceeds the safe range of Complex_Types.Real but both components of the
final result do not.
Implementation Advice
6. Implementations in which Complex_Types.Real'Signed_Zeros is True should
attempt to provide a rational treatment of the signs of zero results and
result components. For example, many of the complex elementary functions
have components that are odd functions of one of the parameter
components; in these cases, the result component should have the sign of
the parameter component at the origin. Other complex elementary functions
have zero components whose sign is opposite that of a parameter component
at the origin, or is always positive or always negative.
ΓòÉΓòÉΓòÉ 23.1.3. Complex Input-Output ΓòÉΓòÉΓòÉ
1. The generic package Text_IO.Complex_IO defines procedures for the
formatted input and output of complex values. The generic actual
parameter in an instantiation of Text_IO.Complex_IO is an instance of
Numerics.Generic_Complex_Types for some floating point subtype.
Exceptional conditions are reported by raising the appropriate exception
defined in Text_IO.
Static Semantics
2. The generic library package Text_IO.Complex_IO has the following
declaration:
3.
with Ada.Numerics.Generic_Complex_Types;
generic
with package Complex_Types is new
Ada.Numerics.Generic_Complex_Types (<>);
package Ada.Text_IO.Complex_IO is
4.
use Complex_Types;
5.
Default_Fore : Field := 2;
Default_Aft : Field := Real'Digits - 1;
Default_Exp : Field := 3;
6.
procedure Get (File : in File_Type;
Item : out Complex;
Width : in Field := 0);
procedure Get (Item : out Complex;
Width : in Field := 0);
7.
procedure Put (File : in File_Type;
Item : in Complex;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
procedure Put (Item : in Complex;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
8.
procedure Get (From : in String;
Item : out Complex;
Last : out Positive);
procedure Put (To : out String;
Item : in Complex;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
9.
end Ada.Text_IO.Complex_IO;
10. The semantics of the Get and Put procedures are as follows:
11.
procedure Get (File : in File_Type;
Item : out Complex;
Width : in Field := 0);
procedure Get (Item : out Complex;
Width : in Field := 0);
a. The input sequence is a pair of optionally signed real literals
representing the real and imaginary components of a complex value;
optionally, the pair of components may be separated by a comma
and/or surrounded by a pair of parentheses. Blanks are freely
allowed before each of the components and before the parentheses and
comma, if either is used. If the value of the parameter Width is
zero, then
1. line and page terminators are also allowed in these places;
2. the components shall be separated by at least one blank or line
terminator if the comma is omitted; and
3. reading stops when the right parenthesis has been read, if the
input sequence includes a left parenthesis, or when the
imaginary component has been read, otherwise.
If a nonzero value of Width is supplied, then
1. the components shall be separated by at least one blank if the
comma is omitted; and
2. exactly Width characters are read, or the characters (possibly
none) up to a line terminator, whichever comes first (blanks
are included in the count).
a. Returns, in the parameter Item, the value of type Complex that
corresponds to the input sequence.
b. The exception Text_IO.Data_Error is raised if the input sequence
does not have the required syntax or if the components of the
complex value obtained are not of the base subtype of
Complex_Types.Real.
1.
procedure Put (File : in File_Type;
Item : in Complex;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
procedure Put (Item : in Complex;
Fore : in Field := Default_Fore;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
a. Outputs the value of the parameter Item as a pair of decimal
literals representing the real and imaginary components of the
complex value, using the syntax of an aggregate. More specifically,
1. outputs a left parenthesis;
2. outputs the value of the real component of the parameter Item
with the format defined by the corresponding Put procedure of
an instance of Text_IO.Float_IO for the base subtype of
Complex_Types.Real, using the given values of Fore, Aft, and
Exp;
3. outputs a comma;
4. outputs the value of the imaginary component of the parameter
Item with the format defined by the corresponding Put procedure
of an instance of Text_IO.Float_IO for the base subtype of
Complex_Types.Real, using the given values of Fore, Aft, and
Exp;
5. outputs a right parenthesis.
1.
procedure Get (From : in String;
Item : out Complex;
Last : out Positive);
a. Reads a complex value from the beginning of the given string,
following the same rule as the Get procedure that reads a complex
value from a file, but treating the end of the string as a line
terminator. Returns, in the parameter Item, the value of type
Complex that corresponds to the input sequence. Returns in Last the
index value such that From(Last) is the last character read.
b. The exception Text_IO.Data_Error is raised if the input sequence
does not have the required syntax or if the components of the
complex value obtained are not of the base subtype of
Complex_Types.Real.
1.
procedure Put (To : out String;
Item : in Complex;
Aft : in Field := Default_Aft;
Exp : in Field := Default_Exp);
a. Outputs the value of the parameter Item to the given string as a
pair of decimal literals representing the real and imaginary
components of the complex value, using the syntax of an aggregate.
More specifically,
1. a left parenthesis, the real component, and a comma are left
justified in the given string, with the real component having
the format defined by the Put procedure (for output to a file)
of an instance of Text_IO.Float_IO for the base subtype of
Complex_Types.Real, using a value of zero for Fore and the
given values of Aft and Exp;
2. the imaginary component and a right parenthesis are right
justified in the given string, with the imaginary component
having the format defined by the Put procedure (for output to a
file) of an instance of Text_IO.Float_IO for the base subtype
of Complex_Types.Real, using a value for Fore that completely
fills the remainder of the string, together with the given
values of Aft and Exp.
a. The exception Text_IO.Layout_Error is raised if the given string is
too short to hold the formatted output.
Implementation Permissions
1. Other exceptions declared (by renaming) in Text_IO may be raised by the
preceding procedures in the appropriate circumstances, as for the
corresponding procedures of Text_IO.Float_IO.
ΓòÉΓòÉΓòÉ 23.1.4. The Package Wide_Text_IO.Complex_IO ΓòÉΓòÉΓòÉ
Static Semantics
1. Implementations shall also provide the generic library package
Wide_Text_IO.Complex_IO. Its declaration is obtained from that of
Text_IO.Complex_IO by systematically replacing Text_IO by Wide_Text_IO
and String by Wide_String; the description of its behavior is obtained by
additionally replacing references to particular characters (commas,
parentheses, etc.) by those for the corresponding wide characters.
ΓòÉΓòÉΓòÉ 23.2. Numeric Performance Requirements ΓòÉΓòÉΓòÉ
Implementation Requirements
1. Implementations shall provide a user-selectable mode in which the
accuracy and other numeric performance requirements detailed in the
following subclauses are observed. This mode, referred to as the strict
mode, may or may not be the default mode; it directly affects the results
of the predefined arithmetic operations of real types and the results of
the subprograms in children of the Numerics package, and indirectly
affects the operations in other language defined packages.
Implementations shall also provide the opposing mode, which is known as
the relaxed mode.
Implementation Permissions
2. Either mode may be the default mode.
3. The two modes need not actually be different.
G.2.1 Model of Floating Point Arithmetic
G.2.2 Model-Oriented Attributes of Floating Point
Types
G.2.3 Model of Fixed Point Arithmetic
G.2.4 Accuracy Requirements for the Elementary
Functions
G.2.5 Performance Requirements for Random Number
Generation
G.2.6 Accuracy Requirements for Complex Arithmetic
ΓòÉΓòÉΓòÉ 23.2.1. Model of Floating Point Arithmetic ΓòÉΓòÉΓòÉ
1. In the strict mode, the predefined operations of a floating point type
shall satisfy the accuracy requirements specified here and shall avoid or
signal overflow in the situations described. This behavior is presented
in terms of a model of floating point arithmetic that builds on the
concept of the canonical form, see A.5.3.
Static Semantics
2. Associated with each floating point type is an infinite set of model
numbers. The model numbers of a type are used to define the accuracy
requirements that have to be satisfied by certain predefined operations
of the type; through certain attributes of the model numbers, they are
also used to explain the meaning of a user-declared floating point type
declaration. The model numbers of a derived type are those of the parent
type; the model numbers of a subtype are those of its type.
3. The model numbers of a floating point type T are zero and all the values
expressible in the canonical form (for the type T), in which mantissa has
T'Model_Mantissa digits and exponent has a value greater than or equal to
T'Model_Emin. (These attributes are defined in G.2.2.)
4. A model interval of a floating point type is any interval whose bounds
are model numbers of the type. The model interval of a type T associated
with a value v is the smallest model interval of T that includes v. (The
model interval associated with a model number of a type consists of that
number only.)
Implementation Requirements
5. The accuracy requirements for the evaluation of certain predefined
operations of floating point types are as follows.
6. An operand interval is the model interval, of the type specified for the
operand of an operation, associated with the value of the operand.
7. For any predefined arithmetic operation that yields a result of a
floating point type T, the required bounds on the result are given by a
model interval of T (called the result interval) defined in terms of the
operand values as follows:
a. The result interval is the smallest model interval of T that
includes the minimum and the maximum of all the values obtained by
applying the (exact) mathematical operation to values arbitrarily
selected from the respective operand intervals.
1. The result interval of an exponentiation is obtained by applying the
above rule to the sequence of multiplications defined by the exponent,
assuming arbitrary association of the factors, and to the final division
in the case of a negative exponent.
2. The result interval of a conversion of a numeric value to a floating
point type T is the model interval of T associated with the operand
value, except when the source expression is of a fixed point type with a
small that is not a power of T'Machine_Radix or is a fixed point
multiplication or division either of whose operands has a small that is
not a power of T'Machine_Radix; in these cases, the result interval is
implementation defined.
3. For any of the foregoing operations, the implementation shall deliver a
value that belongs to the result interval when both bounds of the result
interval are in the safe range of the result type T, as determined by the
values of T'Safe_First and T'Safe_Last; otherwise,
a. if T'Machine_Overflows is True, the implementation shall either
deliver a value that belongs to the result interval or raise
Constraint_Error;
b. if T'Machine_Overflows is False, the result is implementation
defined.
1. For any predefined relation on operands of a floating point type T, the
implementation may deliver any value (i.e., either True or False)
obtained by applying the (exact) mathematical comparison to values
arbitrarily chosen from the respective operand intervals.
2. The result of a membership test is defined in terms of comparisons of the
operand value with the lower and upper bounds of the given range or type
mark (the usual rules apply to these comparisons).
Implementation Permissions
3. If the underlying floating point hardware implements division as
multiplication by a reciprocal, the result interval for division (and
exponentiation by a negative exponent) is implementation defined.
ΓòÉΓòÉΓòÉ 23.2.2. Model-Oriented Attributes of Floating Point Types ΓòÉΓòÉΓòÉ
1. In implementations that support the Numerics Annex, the model-oriented
attributes of floating point types shall yield the values defined here,
in both the strict and the relaxed modes. These definitions add
conditions to those in A.5.3.
Static Semantics
2. For every subtype S of a floating point type T:
3. S'Model_Mantissa
Yields the number of digits in the mantissa of the
canonical form of the model numbers of T, see A.5.3.
The value of this attribute shall be greater than or
equal to Ceiling(d*log (10)/log (T'Machine_Radix))+1,
where d is the requested decimal precision of T. In
addition, it shall be less than or equal to the value of
T'Machine_Mantissa. This attribute yields a value of the
type universal_integer.
4. S'Model_Emin
Yields the minimum exponent of the canonical form of the model
numbers of T, see A.5.3. The value of this attribute shall
be greater than or equal to the value of T'Machine_Emin. This
attribute yields a value of the type universal_integer.
5. S'Safe_First
Yields the lower bound of the safe range of T. The value of
this attribute shall be a model number of T and greater than
or equal to the lower bound of the base range of T. In
addition, if T is declared by a floating_point_definition or
is derived from such a type, and the
floating_point_definition includes a real_range_specification
specifying a lower bound of lb, then the value of this
attribute shall be less than or equal to lb; otherwise, it
shall be less than or equal to -10.0 ** (4*d), where d is the
requested decimal precision of T. This attribute yields a
value of the type universal_real.
6. S'Safe_Last
Yields the upper bound of the safe range of T. The value of
this attribute shall be a model number of T and less than or
equal to the upper bound of the base range of T. In
addition, if T is declared by a floating_point_definition or
is derived from such a type, and the floating_point_definition
includes a real_range_specification specifying an
upper bound of ub, then the value of this attribute shall be
greater than or equal to ub; otherwise, it shall be greater
than or equal to 10.0 ** (4*d), where d is the requested
decimal precision of T. This attribute yields a value of the
type universal_real.
7. S'Model
Denotes a function (of a parameter X) whose specification is
given in A.5.3. If X is a model number of T, the
function yields X; otherwise, it yields the value obtained by
rounding or truncating X to either one of the adjacent model
numbers of T. Constraint_Error is raised if the resulting model
number is outside the safe range of S. A zero result has the
sign of X when S'Signed_Zeros is True.
8. Subject to the constraints given above, the values of S'Model_Mantissa
and S'Safe_Last are to be maximized, and the values of S'Model_Emin and
S'Safe_First minimized, by the implementation as follows:
a. First, S'Model_Mantissa is set to the largest value for which values
of S'Model_Emin, S'Safe_First, and S'Safe_Last can be chosen so that
the implementation satisfies the strict-mode requirements of G.2.1,
in terms of the model numbers and safe range induced by these
attributes.
b. Next, S'Model_Emin is set to the smallest value for which values of
S'Safe_First and S'Safe_Last can be chosen so that the
implementation satisfies the strict-mode requirements of G.2.1, in
terms of the model numbers and safe range induced by these
attributes and the previously determined value of S'Model_Mantissa.
c. Finally, S'Safe_First and S'Safe_last are set (in either order) to
the smallest and largest values, respectively, for which the
implementation satisfies the strict-mode requirements of G.2.1, in
terms of the model numbers and safe range induced by these
attributes and the previously determined values of S'Model_Mantissa
and S'Model_Emin.
ΓòÉΓòÉΓòÉ 23.2.3. Model of Fixed Point Arithmetic ΓòÉΓòÉΓòÉ
1. In the strict mode, the predefined arithmetic operations of a fixed point
type shall satisfy the accuracy requirements specified here and shall
avoid or signal overflow in the situations described.
Implementation Requirements
2. The accuracy requirements for the predefined fixed point arithmetic
operations and conversions, and the results of relations on fixed point
operands, are given below.
3. The operands of the fixed point adding operators, absolute value, and
comparisons have the same type. These operations are required to yield
exact results, unless they overflow.
4. Multiplications and divisions are allowed between operands of any two
fixed point types; the result has to be (implicitly or explicitly)
converted to some other numeric type. For purposes of defining the
accuracy rules, the multiplication or division and the conversion are
treated as a single operation whose accuracy depends on three types
(those of the operands and the result). For decimal fixed point types,
the attribute T'Round may be used to imply explicit conversion with
rounding, see 3.5.10.
5. When the result type is a floating point type, the accuracy is as given
in G.2.1. For some combinations of the operand and result types in the
remaining cases, the result is required to belong to a small set of
values called the perfect result set; for other combinations, it is
required merely to belong to a generally larger and
implementation-defined set of values called the close result set. When
the result type is a decimal fixed point type, the perfect result set
contains a single value; thus, operations on decimal types are always
fully specified.
6. When one operand of a fixed-fixed multiplication or division is of type
universal_real, that operand is not implicitly converted in the usual
sense, since the context does not determine a unique target type, but the
accuracy of the result of the multiplication or division (i.e., whether
the result has to belong to the perfect result set or merely the close
result set) depends on the value of the operand of type universal_real
and on the types of the other operand and of the result.
7. For a fixed point multiplication or division whose (exact) mathematical
result is v, and for the conversion of a value v to a fixed point type,
the perfect result set and close result set are defined as follows:
a. If the result type is an ordinary fixed point type with a small of
s,
a. if v is an integer multiple of s, then the perfect result
set contains only the value v;
b. otherwise, it contains the integer multiple of s just
below v and the integer multiple of s just above v.
1. The close result set is an implementation-defined set of
consecutive integer multiples of s containing the perfect
result set as a subset.
a. If the result type is a decimal type with a small of s,
a. if v is an integer multiple of s, then the perfect result
set contains only the value v;
b. otherwise, if truncation applies then it contains only the
integer multiple of s in the direction toward zero,
whereas if rounding applies then it contains only the
nearest integer multiple of s (with ties broken by
rounding away from zero).
1. The close result set is an implementation-defined set of
consecutive integer multiples of s containing the perfect
result set as a subset.
a. If the result type is an integer type,
a. if v is an integer, then the perfect result set contains
only the value v;
b. otherwise, it contains the integer nearest to the value v
(if v lies equally distant from two consecutive integers,
the perfect result set contains the one that is further
from zero).
1. The close result set is an implementation-defined set of
consecutive integers containing the perfect result set as a
subset.
1. The result of a fixed point multiplication or division shall belong
either to the perfect result set or to the close result set, as described
below, if overflow does not occur. In the following cases, if the result
type is a fixed point type, let s be its small; otherwise, i.e. when the
result type is an integer type, let s be 1.0.
a. For a multiplication or division neither of whose operands is of
type universal_real, let l and r be the smalls of the left and right
operands. For a multiplication, if (l*r)/s is an integer or the
reciprocal of an integer (the smalls are said to be ``compatible''
in this case), the result shall belong to the perfect result set;
otherwise, it belongs to the close result set. For a division, if
l/(r*s) is an integer or the reciprocal of an integer (i.e., the
smalls are compatible), the result shall belong to the perfect
result set; otherwise, it belongs to the close result set.
b. For a multiplication or division having one universal_real operand
with a value of v, note that it is always possible to factor v as an
integer multiple of a ``compatible'' small, but the integer multiple
may be ``too big.'' If there exists a factorization in which that
multiple is less than some implementation-defined limit, the result
shall belong to the perfect result set; otherwise, it belongs to the
close result set.
1. A multiplication P * Q of an operand of a fixed point type F by an
operand of an integer type I, or vice-versa, and a division P / Q of an
operand of a fixed point type F by an operand of an integer type I, are
also allowed. In these cases, the result has a type of F; explicit
conversion of the result is never required. The accuracy required in
these cases is the same as that required for a multiplication F(P * Q) or
a division F(P / Q) obtained by interpreting the operand of the integer
type to have a fixed point type with a small of 1.0.
2. The accuracy of the result of a conversion from an integer or fixed point
type to a fixed point type, or from a fixed point type to an integer
type, is the same as that of a fixed point multiplication of the source
value by a fixed point operand having a small of 1.0 and a value of 1.0,
as given by the foregoing rules. The result of a conversion from a
floating point type to a fixed point type shall belong to the close
result set. The result of a conversion of a universal_real operand to a
fixed point type shall belong to the perfect result set.
3. The possibility of overflow in the result of a predefined arithmetic
operation or conversion yielding a result of a fixed point type T is
analogous to that for floating point types, except for being related to
the base range instead of the safe range. If all of the permitted results
belong to the base range of T, then the implementation shall deliver one
of the permitted results; otherwise,
a. if T'Machine_Overflows is True, the implementation shall either
deliver one of the permitted results or raise Constraint_Error;
b. if T'Machine_Overflows is False, the result is implementation
defined.
ΓòÉΓòÉΓòÉ 23.2.4. Accuracy Requirements for the Elementary Functions ΓòÉΓòÉΓòÉ
1. In the strict mode, the performance of
Numerics.Generic_Elementary_Functions shall be as specified here.
Implementation Requirements
2. When an exception is not raised, the result of evaluating a function in
an instance EF of Numerics.Generic_Elementary_Functions belongs to a
result interval, defined as the smallest model interval of EF.Float_Type
that contains all the values of the form f*(1.0+d), where f is the exact
value of the corresponding mathematical function at the given parameter
values, d is a real number, and |d| is less than or equal to the
function's maximum relative error. The function delivers a value that
belongs to the result interval when both of its bounds belong to the safe
range of EF.Float_Type; otherwise,
a. if EF.Float_Type'Machine_Overflows is True, the function either
delivers a value that belongs to the result interval or raises
Constraint_Error, signaling overflow;
b. if EF.Float_Type'Machine_Overflows is False, the result is
implementation defined.
1. The maximum relative error exhibited by each function is as follows:
a. 2.0*EF.Float_Type'Model_Epsilon, in the case of the Sqrt, Sin, and
Cos functions;
b. 4.0*EF.Float_Type'Model_Epsilon, in the case of the Log, Exp, Tan,
Cot, and inverse trigonometric functions; and
c. 8.0*EF.Float_Type'Model_Epsilon, in the case of the forward and
inverse hyperbolic functions.
1. The maximum relative error exhibited by the exponentiation operator,
which depends on the values of the operands, is (4.0+|Right*log
(Left)|/32.0)*EF.Float_Type'Model_Epsilon.
2. The maximum relative error given above applies throughout the domain of
the forward trigonometric functions when the Cycle parameter is
specified. When the Cycle parameter is omitted, the maximum relative
error given above applies only when the absolute value of the angle
parameter X is less than or equal to some implementation-defined angle
threshold, which shall be at least EF.Float_Type'Machine_Radix **
Floor(EF.Float_Type'Machine_Mantissa/2). Beyond the angle threshold, the
accuracy of the forward trigonometric functions is implementation
defined.
3. The prescribed results specified in A.5.1, for certain functions at
particular parameter values take precedence over the maximum relative
error bounds; effectively, they narrow to a single value the result
interval allowed by the maximum relative error bounds. Additional rules
with a similar effect are given by the table below for the inverse
trigonometric functions, at particular parameter values for which the
mathematical result is possibly not a model number of EF.Float_Type (or
is, indeed, even transcendental). In each table entry, the values of the
parameters are such that the result lies on the axis between two
quadrants; the corresponding accuracy rule, which takes precedence over
the maximum relative error bounds, is that the result interval is the
model interval of EF.Float_Type associated with the exact mathematical
result given in the table.
4.
+--------------------------------------------------------------+
| |
| Tightly Approximated Elementary Function Results |
| |
+-----------------+----------+----------+------------+-------- +
| | | | | |
| | | | Exact | Exact |
| | | | Result | Result |
| | Value of | Value of | when Cycle | when |
| Function | X | Y | Specified | Cycle |
| | | | | Omitted |
| | | | | |
+-----------------+----------+----------+------------+---------+
| | | | | |
| Arcsin | 1.0 | n.a. | Cycle/4.0 | Pi/2.0 |
| | | | | |
| Arcsin | -1.0 | n.a. | -Cycle/4.0 | -Pi/2.0 |
| | | | | |
| Arccos | 0.0 | n.a. | Cycle/4.0 | Pi/2.0 |
| | | | | |
| Arccos | -1.0 | n.a. | Cycle/2.0 | Pi |
| | | | | |
| Arctan & Arccot | 0.0 | positive | Cycle/4.0 | Pi/2.0 |
| | | | | |
| Arctan & Arccot | 0.0 | negative | -Cycle/4.0 | -Pi/2.0 |
| | | | | |
| Arctan & Arccot | negative | +0.0 | Cycle/2.0 | Pi |
| | | | | |
| Arctan & Arccot | negative | -0.0 | -Cycle/2.0 | -Pi |
| | | | | |
| Arctan & Arccot | negative | 0.0 | Cycle/2.0 | Pi |
| | | | | |
+-----------------+----------+----------+------------+---------+
5. The last line of the table is meant to apply when EF.Float_Type'Signed_
Zeros is False; the two lines just above it, when
EF.Float_Type'Signed_Zeros is True and the parameter Y has a zero value
with the indicated sign.
6. The amount by which the result of an inverse trigonometric function is
allowed to spill over into a quadrant adjacent to the one corresponding
to the principal branch, as given in A.5.1, is limited. The rule is that
the result belongs to the smallest model interval of EF.Float_Type that
contains both boundaries of the quadrant corresponding to the principal
branch. This rule also takes precedence over the maximum relative error
bounds, effectively narrowing the result interval allowed by them.
7. Finally, the following specifications also take precedence over the
maximum relative error bounds:
a. The absolute value of the result of the Sin, Cos, and Tanh functions
never exceeds one.
b. The absolute value of the result of the Coth function is never less
than one.
c. The result of the Cosh function is never less than one.
Implementation Advice
1. The versions of the forward trigonometric functions without a Cycle
parameter should not be implemented by calling the corresponding version
with a Cycle parameter of 2.0*Numerics.Pi, since this will not provide
the required accuracy in some portions of the domain. For the same
reason, the version of Log without a Base parameter should not be
implemented by calling the corresponding version with a Base parameter of
Numerics.e.
ΓòÉΓòÉΓòÉ 23.2.5. Performance Requirements for Random Number Generation ΓòÉΓòÉΓòÉ
1. In the strict mode, the performance of Numerics.Float_Random and
Numerics.Discrete_Random shall be as specified here.
Implementation Requirements
2. Two different calls to the time-dependent Reset procedure shall reset the
generator to different states, provided that the calls are separated in
time by at least one second and not more than fifty years.
3. The implementation's representations of generator states and its
algorithms for generating random numbers shall yield a period of at least
2**31-2; much longer periods are desirable but not required.
4. The implementations of Numerics.Float_Random.Random and
Numerics.Discrete_Random.Random shall pass at least 85% of the individual
trials in a suite of statistical tests. For Numerics.Float_Random, the
tests are applied directly to the floating point values generated (i.e.,
they are not converted to integers first), while for
Numerics.Discrete_Random they are applied to the generated values of
various discrete types. Each test suite performs 6 different tests, with
each test repeated 10 times, yielding a total of 60 individual trials. An
individual trial is deemed to pass if the chi-square value (or other
statistic) calculated for the observed counts or distribution falls
within the range of values corresponding to the 2.5 and 97.5 percentage
points for the relevant degrees of freedom (i.e., it shall be neither too
high nor too low). For the purpose of determining the degrees of freedom,
measurement categories are combined whenever the expected counts are
fewer than 5.
ΓòÉΓòÉΓòÉ 23.2.6. Accuracy Requirements for Complex Arithmetic ΓòÉΓòÉΓòÉ
1. In the strict mode, the performance of Numerics.Generic_Complex_Types and
Numerics.Generic_Complex_Elementary_Functions shall be as specified here.
Implementation Requirements
2. When an exception is not raised, the result of evaluating a real function
of an instance CT of Numerics.Generic_Complex_Types (i.e., a function
that yields a value of subtype CT.Real'Base or CT.Imaginary) belongs to a
result interval defined as for a real elementary function (see G.2.4).
3. When an exception is not raised, each component of the result of
evaluating a complex function of such an instance, or of an instance of
Numerics.Generic_Complex_Elementary_Functions obtained by instantiating
the latter with CT (i.e., a function that yields a value of subtype
CT.Complex), also belongs to a result interval. The result intervals for
the components of the result are either defined by a maximum relative
error bound or by a maximum box error bound. When the result interval for
the real (resp., imaginary) component is defined by maximum relative
error, it is defined as for that of a real function, relative to the
exact value of the real (resp., imaginary) part of the result of the
corresponding mathematical function. When defined by maximum box error,
the result interval for a component of the result is the smallest model
interval of CT.Real that contains all the values of the corresponding
part of f*(1.0+d), where f is the exact complex value of the
corresponding mathematical function at the given parameter values, d is
complex, and |d| is less than or equal to the given maximum box error.
The function delivers a value that belongs to the result interval (or a
value both of whose components belong to their respective result
intervals) when both bounds of the result interval(s) belong to the safe
range of CT.Real; otherwise,
a. if CT.Real'Machine_Overflows is True, the function either delivers a
value that belongs to the result interval (or a value both of whose
components belong to their respective result intervals) or raises
Constraint_Error, signaling overflow;
b. if CT.Real'Machine_Overflows is False, the result is implementation
defined.
1. The error bounds for particular complex functions are tabulated below. In
the table, the error bound is given as the coefficient of
CT.Real'Model_Epsilon.
2.
+-----------------------------------------------------------------+
| |
| Error Bounds for Particular Complex Functions |
| |
+-----------------------------+---------+-----------------+-------+
| | | | |
| | Nature | Nature of | Error |
| Function or Operator | of | Bound | Bound |
| | Result | | |
| | | | |
+-----------------------------+---------+-----------------+-------+
| | | | |
| Modulus | real | max. rel. error | 3.0 |
| | | | |
| Argument | real | max. rel. error | 4.0 |
| | | | |
| Compose_From_Polar | complex | max. rel. error | 3.0 |
| | | | |
| "*" (both operands complex) | complex | max. box error | 5.0 |
| | | | |
| "/" (right operand complex) | complex | max. box error | 13.0 |
| | | | |
| Sqrt | complex | max. rel. error | 6.0 |
| | | | |
| Log | complex | max. box error | 13.0 |
| | | | |
| Exp (complex parameter) | complex | max. rel. error | 7.0 |
| | | | |
| Exp (imaginary parameter) | complex | max. rel. error | 2.0 |
| | | | |
| Sin, Cos, Sinh, and Cosh | complex | max. rel. error | 11.0 |
| | | | |
| Tan, Cot, Tanh, and Coth | complex | max. rel. error | 35.0 |
| | | | |
| inverse trigonometric | complex | max. rel. error | 14.0 |
| | | | |
| inverse hyperbolic | complex | max. rel. error | 14.0 |
| | | | |
+-----------------------------+---------+-----------------+-------+
3. The maximum relative error given above applies throughout the domain of
the Compose_From_Polar function when the Cycle parameter is specified.
When the Cycle parameter is omitted, the maximum relative error applies
only when the absolute value of the parameter Argument is less than or
equal to the angle threshold, see G.2.4. For the Exp function, and for
the forward hyperbolic (resp., trigonometric) functions, the maximum
relative error given above likewise applies only when the absolute value
of the imaginary (resp., real) component of the parameter X (or the
absolute value of the parameter itself, in the case of the Exp function
with a parameter of pure-imaginary type) is less than or equal to the
angle threshold. For larger angles, the accuracy is implementation
defined.
4. The prescribed results specified in G.1.2, for certain functions at
particular parameter values take precedence over the error bounds;
effectively, they narrow to a single value the result interval allowed by
the error bounds for a component of the result. Additional rules with a
similar effect are given below for certain inverse trigonometric and
inverse hyperbolic functions, at particular parameter values for which a
component of the mathematical result is transcendental. In each case, the
accuracy rule, which takes precedence over the error bounds, is that the
result interval for the stated result component is the model interval of
CT.Real associated with the component's exact mathematical value. The
cases in question are as follows:
a. When the parameter X has the value zero, the real (resp., imaginary)
component of the result of the Arccot (resp., Arccoth) function is
in the model interval of CT.Real associated with the value Pi/2.0.
b. When the parameter X has the value one, the real component of the
result of the Arcsin function is in the model interval of CT.Real
associated with the value Pi/2.0.
c. When the parameter X has the value -1.0, the real component of the
result of the Arcsin (resp., Arccos) function is in the model
interval of CT.Real associated with the value -Pi/2.0 (resp., Pi).
1. The amount by which a component of the result of an inverse trigonometric
or inverse hyperbolic function is allowed to spill over into a quadrant
adjacent to the one corresponding to the principal branch, as given in
G.1.2, is limited. The rule is that the result belongs to the smallest
model interval of CT.Real that contains both boundaries of the quadrant
corresponding to the principal branch. This rule also takes precedence to
the maximum error bounds, effectively narrowing the result interval
allowed by them.
2. Finally, the results allowed by the error bounds are narrowed by one
further rule: The absolute value of each component of the result of the
Exp function, for a pure-imaginary parameter, never exceeds one.
Implementation Advice
3. The version of the Compose_From_Polar function without a Cycle parameter
should not be implemented by calling the corresponding version with a
Cycle parameter of 2.0*Numerics.Pi, since this will not provide the
required accuracy in some portions of the domain.
ΓòÉΓòÉΓòÉ 24. Safety and Security (normative) ΓòÉΓòÉΓòÉ
1. This Annex addresses requirements for systems that are safety critical or
have security constraints. It provides facilities and specifies
documentation requirements that relate to several needs:
a. Understanding program execution;
b. Reviewing object code;
c. Restricting language constructs whose usage might complicate the
demonstration of program correctness
Execution understandability is supported by pragma Normalize_Scalars, and
also by requirements for the implementation to document the effect of a
program in the presence of a bounded error or where the language rules leave
the effect unspecified.
1. The pragmas Reviewable and Restrictions relate to the other requirements
addressed by this Annex.
NOTES
2. (1) The Valid attribute, see 13.9.2, is also useful in addressing these
needs, to avoid problems that could otherwise arise from scalars that
have values outside their declared range constraints.
H.1 Pragma Normalize_Scalars
H.2 Documentation of Implementation Decisions
H.3 Reviewable Object Code
H.4 Safety and Security Restrictions --- The
Detailed Node Listing ---
H.1 Pragma Normalize_Scalars
H.2 Documentation of Implementation Decisions
H.3 Reviewable Object Code
H.3.1 Pragma Reviewable
H.3.2 Pragma Inspection_Point
H.4 Safety and Security Restrictions
ΓòÉΓòÉΓòÉ 24.1. Pragma Normalize_Scalars ΓòÉΓòÉΓòÉ
1. This pragma ensures that an otherwise uninitialized scalar object is set
to a predictable value, but out of range if possible.
Syntax
2. The form of a pragma Normalize_Scalars is as follows:
3.
pragma Normalize_Scalars;
Post-Compilation Rules
4. Pragma Normalize_Scalars is a configuration pragma. It applies to all
compilation_units included in a partition.
Documentation Requirements
5. If a pragma Normalize_Scalars applies, the implementation shall document
the implicit initial value for scalar subtypes, and shall identify each
case in which such a value is used and is not an invalid representation.
Implementation Advice
6. Whenever possible, the implicit initial value for a scalar subtype should
be an invalid representation, see 13.9.1.
NOTES
7. (2) The initialization requirement applies to uninitialized scalar
objects that are subcomponents of composite objects, to allocated
objects, and to stand-alone objects. It also applies to scalar out
parameters. Scalar subcomponents of composite out parameters are
initialized to the corresponding part of the actual, by virtue of 6.4.1.
8. (3) The initialization requirement does not apply to a scalar for which
pragma Import has been specified, since initialization of an imported
object is performed solely by the foreign language environment (see B.1).
9. (4) The use of pragma Normalize_Scalars in conjunction with Pragma
Restrictions(No_Exceptions) may result in erroneous execution (see H.4).
ΓòÉΓòÉΓòÉ 24.2. Documentation of Implementation Decisions ΓòÉΓòÉΓòÉ
Documentation Requirements
1. The implementation shall document the range of effects for each situation
that the language rules identify as either a bounded error or as having
an unspecified effect. If the implementation can constrain the effects of
erroneous execution for a given construct, then it shall document such
constraints. The documentation might be provided either independently of
any compilation unit or partition, or as part of an annotated listing for
a given unit or partition. See also 1.1.3, and 1.1.2.
NOTES
2. (5) Among the situations to be documented are the conventions chosen for
parameter passing, the methods used for the management of run-time
storage, and the method used to evaluate numeric expressions if this
involves extended range or extra precision.
ΓòÉΓòÉΓòÉ 24.3. Reviewable Object Code ΓòÉΓòÉΓòÉ
1. Object code review and validation are supported by pragmas Reviewable and
Inspection_Point.
H.3.1 Pragma Reviewable
H.3.2 Pragma Inspection_Point
ΓòÉΓòÉΓòÉ 24.3.1. Pragma Reviewable ΓòÉΓòÉΓòÉ
1. This pragma directs the implementation to provide information to
facilitate analysis and review of a program's object code, in particular
to allow determination of execution time and storage usage and to
identify the correspondence between the source and object programs.
Syntax
2. The form of a pragma Reviewable is as follows:
3.
pragma Reviewable;
Post-Compilation Rules
4. Pragma Reviewable is a configuration pragma. It applies to all
compilation_units included in a partition.
Implementation Requirements
5. The implementation shall provide the following information for any
compilation unit to which such a pragma applies:
a. Where compiler-generated run-time checks remain;
b. An identification of any construct with a language-defined check
that is recognized prior to run time as certain to fail if executed
(even if the generation of run-time checks has been suppressed);
c. For each reference to a scalar object, an identification of the
reference as either ``known to be initialized,'' or ``possibly
uninitialized,'' independent of whether pragma Normalize_Scalars
applies;
d. Where run-time support routines are implicitly invoked;
e. An object code listing, including:
1. Machine instructions, with relative offsets;
2. Where each data object is stored during its lifetime;
3. Correspondence with the source program, including an
identification of the code produced per declaration and per
statement.
a. An identification of each construct for which the implementation
detects the possibility of erroneous execution;
b. For each subprogram, block, task, or other construct implemented by
reserving and subsequently freeing an area on a run-time stack, an
identification of the length of the fixed-size portion of the area
and an indication of whether the non-fixed size portion is reserved
on the stack or in a dynamically-managed storage region.
1. The implementation shall provide the following information for any
partition to which the pragma applies:
a. An object code listing of the entire partition, including
initialization and finalization code as well as run-time system
components, and with an identification of those instructions and
data that will be relocated at load time;
b. A description of the run-time model relevant to the partition.
The implementation shall provide control- and data-flow information, both
within each compilation unit and across the compilation units of the
partition.
Implementation Advice
1. The implementation should provide the above information in both a
human-readable and machine-readable form, and should document the latter
so as to ease further processing by automated tools.
2. Object code listings should be provided both in a symbolic format and
also in an appropriate numeric format (such as hexadecimal or octal).
NOTES
3. (6) The order of elaboration of library units will be documented even in
the absence of pragma Reviewable, see 10.2.
ΓòÉΓòÉΓòÉ 24.3.2. Pragma Inspection_Point ΓòÉΓòÉΓòÉ
1. An occurrence of a pragma Inspection_Point identifies a set of objects
each of whose values is to be available at the point(s) during program
execution corresponding to the position of the pragma in the compilation
unit. The purpose of such a pragma is to facilitate code validation.
Syntax
2. The form of a pragma Inspection_Point is as follows:
3.
pragma Inspection_Point[(object_name {, object_name})];
Legality Rules
4. A pragma Inspection_Point is allowed wherever a declarative_item or
statement is allowed. Each object_name shall statically denote the
declaration of an object.
Static Semantics
5. An inspection point is a point in the object code corresponding to the
occurrence of a pragma Inspection_Point in the compilation unit. An
object is inspectable at an inspection point if the corresponding pragma
Inspection_Point either has an argument denoting that object, or has no
arguments.
Dynamic Semantics
6. Execution of a pragma Inspection_Point has no effect.
Implementation Requirements
7. Reaching an inspection point is an external interaction with respect to
the values of the inspectable objects at that point, see 1.1.3.
Documentation Requirements
8. For each inspection point, the implementation shall identify a mapping
between each inspectable object and the machine resources (such as memory
locations or registers) from which the object's value can be obtained.
NOTES
9. (7) The implementation is not allowed to perform ``dead store
elimination'' on the last assignment to a variable prior to a point where
the variable is inspectable. Thus an inspection point has the effect of
an implicit reference to each of its inspectable objects.
10. (8) Inspection points are useful in maintaining a correspondence between
the state of the program in source code terms, and the machine state
during the program's execution. Assertions about the values of program
objects can be tested in machine terms at inspection points. Object code
between inspection points can be processed by automated tools to verify
programs mechanically.
11. (9) The identification of the mapping from source program objects to
machine resources is allowed to be in the form of an annotated object
listing, in human-readable or tool-processable form.
ΓòÉΓòÉΓòÉ 24.4. Safety and Security Restrictions ΓòÉΓòÉΓòÉ
1. This clause defines restrictions that can be used with pragma
Restrictions, see 13.12, these facilitate the demonstration of program
correctness by allowing tailored versions of the run-time system.
Static Semantics
2. The following restrictions, the same as in D.7, apply in this Annex:
No_Task_Hierarchy, No_Abort_Statement, No_Implicit_Heap_Allocation,
Max_Task_Entries is 0, Max_Asynchronous_Select_Nesting is 0, and
Max_Tasks is 0. The last three restrictions are checked prior to program
execution.
3. The following additional restrictions apply in this Annex.
4. Tasking-related restriction:
5. No_Protected_Types
There are no declarations of protected types or protected
objects.
6. Memory-management related restrictions:
7. No_Allocators
There are no occurrences of an allocator.
8. No_Local_Allocators
Allocators are prohibited in subprograms, generic sub-programs,
tasks, and entry bodies; instantiations of generic
packages are also prohibited in these contexts.
9. No_Unchecked_Deallocation
Semantic dependence on Unchecked_Deallocation is not allowed.
10. Immediate_Reclamation
Except for storage occupied by objects created by allocators
and not deallocated via unchecked deallocation, any storage
reserved at run time for an object is immediately reclaimed
when the object no longer exists.
11. Exception-related restriction:
12. No_Exceptions
Raise_statements and exception_handlers are not allowed. No
language-defined run-time checks are generated; however, a
run-time check performed automatically by the hardware is
permitted.
13. Other restrictions:
14. No_Floating_Point
Uses of predefined floating point types and operations, and
declarations of new floating point types, are not allowed.
15. No_Fixed_Point
Uses of predefined fixed point types and operations, and
declarations of new fixed point types, are not allowed.
16. No_Unchecked_Conversion
Semantic dependence on the predefined generic
Unchecked_Conversion is not allowed.
17. No_Access_Subprograms
The declaration of access-to-subprogram types is not allowed.
18. No_Unchecked_Access
The Unchecked_Access attribute is not allowed.
19. No_Dispatch
Occurrences of T'Class are not allowed, for any (tagged)
subtype T.
20. No_IO
Semantic dependence on any of the library units
Sequential_IO, Direct_IO, Text_IO, Wide_Text_IO, or Stream_IO
is not allowed.
21. No_Delay
Delay_Statements and semantic dependence on package Calendar
are not allowed.
22. No_Recursion
As part of the execution of a subprogram, the same subprogram
is not invoked.
23. No_Reentrancy
During the execution of a subprogram by a task, no other task
invokes the same subprogram.
Implementation Requirements
24. If an implementation supports pragma Restrictions for a particular
argument, then except for the restrictions No_Unchecked_Deallocation,
No_Unchecked_Conversion, No_Access_Subprograms, and No_Unchecked_Access,
the associated restriction applies to the run-time system.
Documentation Requirements
25. If a pragma Restrictions(No_Exceptions) is specified, the implementation
shall document the effects of all constructs where language-defined
checks are still performed automatically (for example, an overflow check
performed by the processor).
Erroneous Execution
26. Program execution is erroneous if pragma Restrictions(No_Exceptions) has
been specified and the conditions arise under which a generated
language-defined run-time check would fail.
27. Program execution is erroneous if pragma Restrictions(No_Recursion) has
been specified and a subprogram is invoked as part of its own execution,
or if pragma Restrictions(No_Reentrancy) has been specified and during
the execution of a subprogram by a task, another task invokes the same
subprogram.
ΓòÉΓòÉΓòÉ 25. Obsolescent Features (normative) ΓòÉΓòÉΓòÉ
1. This Annex contains descriptions of features of the language whose
functionality is largely redundant with other features defined by this
International Standard. Use of these features is not recommended in newly
written programs.
J.1 Renamings of Ada 83 Library Units
J.2 Allowed Replacements of Characters
J.3 Reduced Accuracy Subtypes
J.4 The Constrained Attribute
J.5 ASCII
J.6 Numeric_Error
J.7 At Clauses
J.8 Mod Clauses
J.9 The Storage_Size Attribute --- The Detailed Node
Listing ---
J.1 Renamings of Ada 83 Library Units
J.2 Allowed Replacements of Characters
J.3 Reduced Accuracy Subtypes
J.4 The Constrained Attribute
J.5 ASCII
J.6 Numeric_Error
J.7 At Clauses
J.7.1 Interrupt Entries
J.8 Mod Clauses
J.9 The Storage_Size Attribute
ΓòÉΓòÉΓòÉ 25.1. Renamings of Ada 83 Library Units ΓòÉΓòÉΓòÉ
Static Semantics
1. The following library_unit_renaming_declarations exist:
2.
with Ada.Unchecked_Conversion;
generic function Unchecked_Conversion
renames Ada.Unchecked_Conversion;
3.
with Ada.Unchecked_Deallocation;
generic procedure Unchecked_Deallocation
renames Ada.Unchecked_Deallocation;
4.
with Ada.Sequential_IO;
generic package Sequential_IO renames Ada.Sequential_IO;
5.
with Ada.Direct_IO;
generic package Direct_IO renames Ada.Direct_IO;
6.
with Ada.Text_IO;
package Text_IO renames Ada.Text_IO;
7.
with Ada.IO_Exceptions;
package IO_Exceptions renames Ada.IO_Exceptions;
8.
with Ada.Calendar;
package Calendar renames Ada.Calendar;
9.
with System.Machine_Code;
package Machine_Code renames System.Machine_Code; -- If supported.
Implementation Requirements
10. The implementation shall allow the user to replace these renamings.
ΓòÉΓòÉΓòÉ 25.2. Allowed Replacements of Characters ΓòÉΓòÉΓòÉ
Syntax
1. The following replacements are allowed for the vertical line, number
sign, and quotation mark characters:
a. A vertical line character (|) can be replaced by an exclamation mark
(!) where used as a delimiter.
b. The number sign characters (#) of a based_literal can be replaced by
colons (:) provided that the replacement is done for both
occurrences.
c. The quotation marks (") used as string brackets at both ends of a
string literal can be replaced by percent signs (%) provided that
the enclosed sequence of characters contains no quotation mark, and
provided that both string brackets are replaced. Any percent sign
within the sequence of characters shall then be doubled and each
such doubled percent sign is interpreted as a single percent sign
character value.
d. These replacements do not change the meaning of the program.
ΓòÉΓòÉΓòÉ 25.3. Reduced Accuracy Subtypes ΓòÉΓòÉΓòÉ
1. A digits_constraint may be used to define a floating point subtype with a
new value for its requested decimal precision, as reflected by its Digits
attribute. Similarly, a delta_constraint may be used to define an
ordinary fixed point subtype with a new value for its delta, as reflected
by its Delta attribute.
Syntax
2.
delta_constraint ::= delta static_expression [range_constraint]
Name Resolution Rules
3. The expression of a delta_constraint is expected to be of any real type.
Legality Rules
4. The expression of a delta_constraint shall be static.
5. For a subtype_indication with a delta_constraint, the subtype_mark shall
denote an ordinary fixed point subtype.
6. For a subtype_indication with a digits_constraint, the subtype_mark shall
denote either a decimal fixed point subtype or a floating point subtype
(notwithstanding the rule given in 3.5.9, that only allows a decimal
fixed point subtype).
Static Semantics
7. A subtype_indication with a subtype_mark that denotes an ordinary fixed
point subtype and a delta_constraint defines an ordinary fixed point
subtype with a delta given by the value of the expression of the
delta_constraint. If the delta_constraint includes a range_constraint,
then the ordinary fixed point subtype is constrained by the
range_constraint.
8. A subtype_indication with a subtype_mark that denotes a floating point
subtype and a digits_constraint defines a floating point subtype with a
requested decimal precision (as reflected by its Digits attribute) given
by the value of the expression of the digits_constraint. If the
digits_constraint includes a range_constraint, then the floating point
subtype is constrained by the range_constraint.
Dynamic Semantics
9. A delta_constraint is compatible with an ordinary fixed point subtype if
the value of the expression is no less than the delta of the subtype, and
the range_constraint, if any, is compatible with the subtype.
10. A digits_constraint is compatible with a floating point subtype if the
value of the expression is no greater than the requested decimal
precision of the subtype, and the range_constraint, if any, is compatible
with the subtype.
11. The elaboration of a delta_constraint consists of the elaboration of the
range_constraint, if any.
ΓòÉΓòÉΓòÉ 25.4. The Constrained Attribute ΓòÉΓòÉΓòÉ
Static Semantics
1. For every private subtype S, the following attribute is defined:
2. S'Constrained
Yields the value False if S denotes an unconstrained
nonformal private subtype with discriminants; also yields the
value False if S denotes a generic formal private subtype,
and the associated actual subtype is either an unconstrained
subtype with discriminants or an unconstrained array subtype;
yields the value True otherwise. The value of this attribute
is of the predefined subtype Boolean.
ΓòÉΓòÉΓòÉ 25.5. ASCII ΓòÉΓòÉΓòÉ
Static Semantics
1. The following declaration exists in the declaration of package Standard:
2.
package ASCII is
3.
-- Control characters:
4.
NUL : constant Character := nul;
SOH : constant Character := soh;
STX : constant Character := stx;
ETX : constant Character := etx;
EOT : constant Character := eot;
ENQ : constant Character := enq;
ACK : constant Character := ack;
BEL : constant Character := bel;
BS : constant Character := bs;
HT : constant Character := ht;
LF : constant Character := lf;
VT : constant Character := vt;
FF : constant Character := ff;
CR : constant Character := cr;
SO : constant Character := so;
SI : constant Character := si;
DLE : constant Character := dle;
DC1 : constant Character := dc1;
DC2 : constant Character := dc2;
DC3 : constant Character := dc3;
DC4 : constant Character := dc4;
NAK : constant Character := nak;
SYN : constant Character := syn;
ETB : constant Character := etb;
CAN : constant Character := can;
EM : constant Character := em;
SUB : constant Character := sub;
ESC : constant Character := esc;
FS : constant Character := fs;
GS : constant Character := gs;
RS : constant Character := rs;
US : constant Character := us;
DEL : constant Character := del;
5.
-- Other characters:
6.
Exclam : constant Character:= '!';
Quotation : constant Character:= '"';
Sharp : constant Character:= '#';
Dollar : constant Character:= '$';
Percent : constant Character:= '%';
Ampersand : constant Character:= '&';
Colon : constant Character:= ':';
Semicolon : constant Character:= ';';
Query : constant Character:= '?';
At_Sign : constant Character:= '@';
L_Bracket : constant Character:= '[';
Back_Slash: constant Character:= '\';
R_Bracket : constant Character:= ']';
Circumflex: constant Character:= '^';
Underline : constant Character:= '_';
Grave : constant Character:= '`';
L_Brace : constant Character:= '{';
Bar : constant Character:= '|';
R_Brace : constant Character:= '}';
Tilde : constant Character:= '~';
7.
-- Lower case letters:
8.
LC_A: constant Character:= 'a';
┬╖┬╖┬╖
LC_Z: constant Character:= 'z';
9.
end ASCII;
ΓòÉΓòÉΓòÉ 25.6. Numeric_Error ΓòÉΓòÉΓòÉ
Static Semantics
1. The following declaration exists in the declaration of package Standard:
2.
Numeric_Error : exception renames Constraint_Error;
ΓòÉΓòÉΓòÉ 25.7. At Clauses ΓòÉΓòÉΓòÉ
Syntax
1.
at_clause ::= for direct_name use at expression;
Static Semantics
2. An at_clause of the form ``for x use at y;'' is equivalent to an
attribute_definition_clause of the form ``for x'Address use y;''.
J.7.1 Interrupt Entries
ΓòÉΓòÉΓòÉ 25.7.1. Interrupt Entries ΓòÉΓòÉΓòÉ
1. Implementations are permitted to allow the attachment of task entries to
interrupts via the address clause. Such an entry is referred to as an
interrupt entry.
2. The address of the task entry corresponds to a hardware interrupt in an
implementation-defined manner. (See Ada.Interrupts.Reference in C.3.2.)
Static Semantics
3. The following attribute is defined:
4. For any task entry X:
5. X'Address
For a task entry whose address is specified (an interrupt
entry), the value refers to the corresponding hardware
interrupt. For such an entry, as for any other task entry,
the meaning of this value is implementation defined. The
value of this attribute is of the type of the subtype
System.Address.
a. Address may be specified for single entries via an
attribute_definition_clause.
Dynamic Semantics
1. As part of the initialization of a task object, the address clause for an
interrupt entry is elaborated, which evaluates the expression of the
address clause. A check is made that the address specified is associated
with some interrupt to which a task entry may be attached. If this check
fails, Program_Error is raised. Otherwise, the interrupt entry is
attached to the interrupt associated with the specified address.
2. Upon finalization of the task object, the interrupt entry, if any, is
detached from the corresponding interrupt and the default treatment is
restored.
3. While an interrupt entry is attached to an interrupt, the interrupt is
reserved, see C.3.
4. An interrupt delivered to a task entry acts as a call to the entry issued
by a hardware task whose priority is in the System.Interrupt_Priority
range. It is implementation defined whether the call is performed as an
ordinary entry call, a timed entry call, or a conditional entry call;
which kind of call is performed can depend on the specific interrupt.
Bounded (Run-Time) Errors
5. It is a bounded error to evaluate E'Caller, see C.7.1, in an
accept_statement for an interrupt entry. The possible effects are the
same as for calling Current_Task from an entry body.
Documentation Requirements
6. The implementation shall document to which interrupts a task entry may be
attached.
7. The implementation shall document whether the invocation of an interrupt
entry has the effect of an ordinary entry call, conditional call, or a
timed call, and whether the effect varies in the presence of pending
interrupts.
Implementation Permissions
8. The support for this subclause is optional.
9. Interrupts to which the implementation allows a task entry to be attached
may be designated as reserved for the entire duration of program
execution; that is, not just when they have an interrupt entry attached
to them.
10. Interrupt entry calls may be implemented by having the hardware execute
directly the appropriate accept body. Alternatively, the implementation
is allowed to provide an internal interrupt handler to simulate the
effect of a normal task calling the entry.
11. The implementation is allowed to impose restrictions on the
specifications and bodies of tasks that have interrupt entries.
12. It is implementation defined whether direct calls (from the program) to
interrupt entries are allowed.
13. If a select_statement contains both a terminate_alternative and an
accept_alternative for an interrupt entry, then an implementation is
allowed to impose further requirements for the selection of the
terminate_alternative in addition to those given in, see 9.3.
NOTES
14. (1) Queued interrupts correspond to ordinary entry calls. Interrupts that
are lost if not immediately processed correspond to conditional entry
calls. It is a consequence of the priority rules that an accept body
executed in response to an interrupt can be executed with the active
priority at which the hardware generates the interrupt, taking precedence
over lower priority tasks, without a scheduling action.
15. (2) Control information that is supplied upon an interrupt can be passed
to an associated interrupt entry as one or more parameters of mode in.
Examples
16. Example of an interrupt entry:
17.
task Interrupt_Handler is
entry Done;
for Done'Address use
Ada.Interrupts.Reference (Ada.Interrupts.Names.Device_Done);
end Interrupt_Handler;
ΓòÉΓòÉΓòÉ 25.8. Mod Clauses ΓòÉΓòÉΓòÉ
Syntax
1.
mod_clause ::= at mod static_expression;
Static Semantics
2. A record_representation_clause of the form:
3.
for r use
record at mod a
┬╖┬╖┬╖
end record;
4. is equivalent to:
5.
for r'Alignment use a;
for r use
record
┬╖┬╖┬╖
end record;
ΓòÉΓòÉΓòÉ 25.9. The Storage_Size Attribute ΓòÉΓòÉΓòÉ
Static Semantics
1. For any task subtype T, the following attribute is defined:
2. T'Storage_Size
Denotes an implementation-defined value of type
universal_integer representing the number of storage
elements reserved for a task of the subtype T.
a. Storage_Size may be specified for a task first subtype via an
attribute_definition_clause.
ΓòÉΓòÉΓòÉ 26. Language-Defined Attributes (informative) ΓòÉΓòÉΓòÉ
1. This annex summarizes the definitions given elsewhere of the
language-defined attributes.
2. P'Access For a prefix P that denotes a subprogram:
a. P'Access yields an access value that designates the subprogram
denoted by P. The type of P'Access is an access-to-subprogram type
(S), as determined by the expected type (see 3.10.2).
1. X'Access For a prefix X that denotes an aliased view of an object:
a. X'Access yields an access value that designates the object denoted
by X. The type of X'Access is an access-to-object type, as
determined by the expected type. The expected type shall be a
general access type (see 3.10.2).
1. X'Address For a prefix X that denotes an object, program unit, or label:
a. Denotes the address of the first of the storage elements allocated
to X. For a program unit or label, this value refers to the machine
code associated with the corresponding body or statement. The value
of this attribute is of type System.Address (see 13.3).
1. S'Adjacent For every subtype S of a floating point type T:
a. S'Adjacent denotes a function with the following specification:
b.
function S'Adjacent (X, Towards : T) return T
c. If Towards=X, the function yields X; otherwise, it yields the
machine number of the type T adjacent to X in the direction of
Towards, if that machine number exists. If the result would be
outside the base range of S, Constraint_Error is raised. When
T'Signed_Zeros is True, a zero result has the sign of X. When
Towards is zero, its sign has no bearing on the result (see A.5.3).
1. S'Aft For every fixed point subtype S:
a. S'Aft yields the number of decimal digits needed after the decimal
point to accommodate the delta of the subtype S, unless the delta of
the subtype S is greater than 0.1, in which case the attribute
yields the value one. (S'Aft is the smallest positive integer N for
which (10**N)*S'Delta is greater than or equal to one.) The value
of this attribute is of the type universal_integer (see 3.5.10).
1. X'Alignment For a prefix X that denotes a subtype or object:
a. The Address of an object that is allocated under control of the
implementation is an integral multiple of the Alignment of the
object (that is, the Address modulo the Alignment is zero). The
offset of a record component is a multiple of the Alignment of the
component. For an object that is not allocated under control of the
implementation (that is, one that is imported, that is allocated by
a user-defined allocator, whose Address has been specified, or is
designated by an access value returned by an instance of
Unchecked_Conversion), the implementation may assume that the
Address is an integral multiple of its Alignment. The implementation
shall not assume a stricter alignment.
b. The value of this attribute is of type universal_integer, and
nonnegative; zero means that the object is not necessarily aligned
on a storage element boundary (see 13.3).
1. S'Base For every scalar subtype S:
a. S'Base denotes an unconstrained subtype of the type of S. This
unconstrained subtype is called the base subtype of the type (see
3.5).
1. S'Bit_Order For every specific record subtype S:
a. Denotes the bit ordering for the type of S. The value of this
attribute is of type System.Bit_Order (see 13.5.3).
1. P'Body_Version For a prefix P that statically denotes a program unit:
a. Yields a value of the predefined type String that identifies the
version of the compilation unit that contains the body (but not any
subunits) of the program unit (see E.3).
1. T'Callable For a prefix T that is of a task type (after any implicit
dereference):
a. Yields the value True when the task denoted by T is callable, and
False otherwise (see 9.9).
1. E'Caller For a prefix E that denotes an entry_declaration:
a. Yields a value of the type Task_ID that identifies the task whose
call is now being serviced. Use of this attribute is allowed only
inside an entry_body or accept_statement corresponding to the
entry_declaration denoted by E (see C.7.1).
1. S'Ceiling For every subtype S of a floating point type T:
a. S'Ceiling denotes a function with the following specification:
b.
function S'Ceiling (X : T) return T
c. The function yields the value Ceiling(X), i.e., the smallest (most
negative) integral value greater than or equal to X. When X is zero,
the result has the sign of X; a zero result otherwise has a negative
sign when S'Signed_Zeros is True (see A.5.3).
1. S'Class For every subtype S of a tagged type T (specific or class-wide):
a. S'Class denotes a subtype of the class-wide type (called T'Class in
this International Standard) for the class rooted at T (or if S
already denotes a class-wide subtype, then S'Class is the same as
S).
b. S'Class is unconstrained. However, if S is constrained, then the
values of S'Class are only those that when converted to the type T
belong to S (see 3.9).
1. S'Class For every subtype S of an untagged private type whose full view
is tagged:
a. Denotes the class-wide subtype corresponding to the full view of S.
This attribute is allowed only from the beginning of the private
part in which the full view is declared, until the declaration of
the full view. After the full view, the Class attribute of the full
view can be used (see 7.3.1).
1. X'Component_Size For a prefix X that denotes an array subtype or array
object (after any implicit dereference):
a. Denotes the size in bits of components of the type of X. The value
of this attribute is of type universal_integer (see 13.3).
1. S'Compose For every subtype S of a floating point type T:
a. S'Compose denotes a function with the following specification:
b.
function S'Compose
(Fraction : T;
Exponent : universal_integer) return T
c. Let v be the value (Fraction*T'Machine_Radix) ** (Exponent-k), where
k is the normalized exponent of Fraction. If v is a machine number
of the type T, or if |v|>=T'Model_Small, the function yields v;
otherwise, it yields either one of the machine numbers of the type T
adjacent to v. Constraint_Error is optionally raised if v is outside
the base range of S. A zero result has the sign of Fraction when
S'Signed_Zeros is True (see A.5.3).
1. A'Constrained For a prefix A that is of a discriminated type (after any
implicit dereference):
a. Yields the value True if A denotes a constant, a value, or a
constrained variable, and False otherwise (see 3.7.2).
1. S'Copy_Sign For every subtype S of a floating point type T:
a. S'Copy_Sign denotes a function with the following specification:
b.
function S'Copy_Sign (Value, Sign : T) return T
c. If the value of Value is nonzero, the function yields a result whose
magnitude is that of Value and whose sign is that of Sign;
otherwise, it yields the value zero. Constraint_Error is optionally
raised if the result is outside the base range of S. A zero result
has the sign of Sign when S'Signed_Zeros is True (see A.5.3).
1. E'Count For a prefix E that denotes an entry of a task or protected
unit:
a. Yields the number of calls presently queued on the entry E of the
current instance of the unit. The value of this attribute is of the
type universal_integer (see 9.9).
1. S'Definite For a prefix S that denotes a formal indefinite subtype:
a. S'Definite yields True if the actual subtype corresponding to S is
definite; otherwise it yields False. The value of this attribute is
of the predefined type Boolean (see 12.5.1).
1. S'Delta For every fixed point subtype S:
a. S'Delta denotes the delta of the fixed point subtype S. The value of
this attribute is of the type universal_real (see 3.5.10).
1. S'Denorm For every subtype S of a floating point type T:
a. Yields the value True if every value expressible in the form
T'Machine_Emin
+/-mantissa*T'Machine_Radix
where mantissa is a nonzero T'Machine_Mantissa-digit fraction in the number
base T'Machine_Radix, the first digit of which is zero, is a machine number,
see 3.5.7, of the type T; yields the value False otherwise. The value of this
attribute is of the predefined type Boolean (see A.5.3).
1. S'Digits For every decimal fixed point subtype S:
a. S'Digits denotes the digits of the decimal fixed point subtype S,
which corresponds to the number of decimal digits that are
representable in objects of the subtype. The value of this attribute
is of the type universal_integer (see 3.5.10).
1. S'Digits For every floating point subtype S:
a. S'Digits denotes the requested decimal precision for the subtype S.
The value of this attribute is of the type universal_integer (see
3.5.8).
1. S'Exponent For every subtype S of a floating point type T:
a. S'Exponent denotes a function with the following specification:
b.
function S'Exponent (X : T) return universal_integer
c. The function yields the normalized exponent of X (see A.5.3).
1. S'External_Tag For every subtype S of a tagged type T (specific or
class-wide):
a. S'External_Tag denotes an external string representation for S'Tag;
it is of the predefined type String. External_Tag may be specified
for a specific tagged type via an attribute_definition_clause; the
expression of such a clause shall be static. The default external
tag representation is implementation defined (see 3.9.2 and
13.13.2). See 13.3.
1. A'First(N) For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'First(N) denotes the lower bound of the N-th index range; its type
is the corresponding index type (see 3.6.2).
1. A'First For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'First denotes the lower bound of the first index range; its type
is the corresponding index type (see 3.6.2).
1. S'First For every scalar subtype S:
a. S'First denotes the lower bound of the range of S. The value of this
attribute is of the type of S. See 3.5.
1. R.C'First_Bit For a component C of a composite, non-array object R:
a. Denotes the offset, from the start of the first of the storage
elements occupied by C, of the first bit occupied by C. This offset
is measured in bits. The first bit of a storage element is numbered
zero. The value of this attribute is of the type universal_integer.
See 13.5.2.
1. S'Floor For every subtype S of a floating point type T:
a. S'Floor denotes a function with the following specification:
b.
function S'Floor (X : T) return T
c. The function yields the value Floor(X), i.e., the largest (most
positive) integral value less than or equal to X. When X is zero,
the result has the sign of X; a zero result otherwise has a positive
sign. See A.5.3.
1. S'Fore For every fixed point subtype S:
a. S'Fore yields the minimum number of characters needed before the
decimal point for the decimal representation of any value of the
subtype S, assuming that the representation does not include an
exponent, but includes a one-character prefix that is either a minus
sign or a space. (This minimum number does not include superfluous
zeros or underlines, and is at least 2.) The value of this
attribute is of the type universal_integer. See 3.5.10.
1. S'Fraction For every subtype S of a floating point type T:
a. S'Fraction denotes a function with the following specification:
b.
function S'Fraction (X : T) return T
c. The function yields the value (X*T'Machine_Radix) ** -k, where k is
the normalized exponent of X. A zero result, which can only occur
when X is zero, has the sign of X. See A.5.3.
1. E'Identity For a prefix E that denotes an exception:
a. E'Identity returns the unique identity of the exception. The type of
this attribute is Exception_Id. See 11.4.1.
1. T'Identity For a prefix T that is of a task type (after any implicit
dereference):
a. Yields a value of the type Task_ID that identifies the task denoted
by T. See C.7.1.
1. S'Image For every scalar subtype S:
a. S'Image denotes a function with the following specification:
b.
function S'Image(Arg : S'Base) return String
c. The function returns an image of the value of Arg as a String. See
3.5.
1. S'Class'Input For every subtype S'Class of a class-wide type T'Class:
a. S'Class'Input denotes a function with the following specification:
b.
function S'Class'Input
(Stream : access Ada.Streams.Root_Stream_Type'Class)
return T'Class
c. First reads the external tag from Stream and determines the
corresponding internal tag (by calling
Tags.Internal_Tag(String'Input(Stream)) -- see 3.9.) and then
dispatches to the subprogram denoted by the Input attribute of the
specific type identified by the internal tag; returns that result.
See 13.13.2.
1. S'Input For every subtype S of a specific type T:
a. S'Input denotes a function with the following specification:
b.
function S'Input
(Stream : access Ada.Streams.Root_Stream_Type'Class)
return T
c. S'Input reads and returns one value from Stream, using any bounds or
discriminants written by a corresponding S'Output to determine how
much to read. See 13.13.2.
1. A'Last(N) For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'Last(N) denotes the upper bound of the N-th index range; its type
is the corresponding index type. See 3.6.2.
1. A'Last For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'Last denotes the upper bound of the first index range; its type is
the corresponding index type. See 3.6.2.
1. S'Last For every scalar subtype S:
a. S'Last denotes the upper bound of the range of S. The value of this
attribute is of the type of S. See 3.5.
1. R.C'Last_Bit For a component C of a composite, non-array object R:
a. Denotes the offset, from the start of the first of the storage
elements occupied by C, of the last bit occupied by C. This offset
is measured in bits. The value of this attribute is of the type
universal_integer. See 13.5.2.
1. S'Leading_Part For every subtype S of a floating point type T:
a. S'Leading_Part denotes a function with the following specification:
b.
function S'Leading_Part
(X : T;
Radix_Digits : universal_integer) return T
c. Let v be the value T'Machine_Radix ** (k-Radix_Digits), where k is
the normalized exponent of X. The function yields the value
1. Floor(X/v)*v, when X is nonnegative and Radix_Digits is
positive;
2. Ceiling(X/v)*v, when X is negative and Radix_Digits is
positive.
a. Constraint_Error is raised when Radix_Digits is zero or negative. A
zero result, which can only occur when X is zero, has the sign of X.
See A.5.3.
1. A'Length(N) For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'Length(N) denotes the number of values of the N-th index range
(zero for a null range); its type is universal_integer. See 3.6.2.
1. A'Length For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'Length denotes the number of values of the first index range (zero
for a null range); its type is universal_integer. See 3.6.2.
1. S'Machine For every subtype S of a floating point type T:
a. S'Machine denotes a function with the following specification:
b.
function S'Machine (X : T) return T
c. If X is a machine number of the type T, the function yields X;
otherwise, it yields the value obtained by rounding or truncating X
to either one of the adjacent machine numbers of the type T.
Constraint_Error is raised if rounding or truncating X to the
precision of the machine numbers results in a value outside the base
range of S. A zero result has the sign of X when S'Signed_Zeros is
True. See A.5.3.
1. S'Machine_Emax For every subtype S of a floating point type T:
a. Yields the largest (most positive) value of exponent such that every
value expressible in the canonical form (for the type T), having a
mantissa of T'Machine_Mantissa digits, is a machine number (see
3.5.7) of the type T. This attribute yields a value of the type
universal_integer. See A.5.3.
1. S'Machine_Emin For every subtype S of a floating point type T:
a. Yields the smallest (most negative) value of exponent such that
every value expressible in the canonical form (for the type T),
having a mantissa of T'Machine_Mantissa digits, is a machine number
(see 3.5.7) of the type T. This attribute yields a value of the type
universal_integer. See A.5.3.
1. S'Machine_Mantissa For every subtype S of a floating point type T:
a. Yields the largest value of p such that every value expressible in
the canonical form (for the type T), having a p-digit mantissa and
an exponent between T'Machine_Emin and T'Machine_Emax, is a machine
number (see 3.5.7) of the type T. This attribute yields a value of
the type universal_integer. See A.5.3.
1. S'Machine_Overflows For every subtype S of a fixed point type T:
a. Yields the value True if overflow and divide-by-zero are detected
and reported by raising Constraint_Error for every predefined
operation that yields a result of the type T; yields the value False
otherwise. The value of this attribute is of the predefined type
Boolean. See A.5.4.
1. S'Machine_Overflows For every subtype S of a floating point type T:
a. Yields the value True if overflow and divide-by-zero are detected
and reported by raising Constraint_Error for every predefined
operation that yields a result of the type T; yields the value False
otherwise. The value of this attribute is of the predefined type
Boolean. See A.5.3.
1. S'Machine_Radix For every subtype S of a fixed point type T:
a. Yields the radix of the hardware representation of the type T. The
value of this attribute is of the type universal_integer. See A.5.4.
1. S'Machine_Radix For every subtype S of a floating point type T:
a. Yields the radix of the hardware representation of the type T. The
value of this attribute is of the type universal_integer. See A.5.3.
1. S'Machine_Rounds For every subtype S of a fixed point type T:
a. Yields the value True if rounding is performed on inexact results of
every predefined operation that yields a result of the type T;
yields the value False otherwise. The value of this attribute is of
the predefined type Boolean. See A.5.4.
1. S'Machine_Rounds For every subtype S of a floating point type T:
a. Yields the value True if rounding is performed on inexact results of
every predefined operation that yields a result of the type T;
yields the value False otherwise. The value of this attribute is of
the predefined type Boolean. See A.5.3.
1. S'Max For every scalar subtype S:
a. S'Max denotes a function with the following specification:
b.
function S'Max(Left, Right : S'Base) return S'Base
c. The function returns the greater of the values of the two
parameters. See 3.5.
1. S'Max_Size_In_Storage_Elements For every subtype S:
a. Denotes the maximum value for Size_In_Storage_Elements that will be
requested via Allocate for an access type whose designated subtype
is S. The value of this attribute is of type universal_integer. See
13.11.1.
1. S'Min For every scalar subtype S:
a. S'Min denotes a function with the following specification:
b.
function S'Min(Left, Right : S'Base) return S'Base
c. The function returns the lesser of the values of the two parameters.
See 3.5.
1. S'Model For every subtype S of a floating point type T:
a. S'Model denotes a function with the following specification:
b.
function S'Model (X : T) return T
c. If the Numerics Annex is not supported, the meaning of this
attribute is implementation defined; see G.2.2 for the definition
that applies to implementations supporting the Numerics Annex. See
A.5.3.
1. S'Model_Emin For every subtype S of a floating point type T:
a. If the Numerics Annex is not supported, this attribute yields an
implementation defined value that is greater than or equal to the
value of T'Machine_Emin. See G.2.2 for further requirements that
apply to implementations supporting the Numerics Annex. The value of
this attribute is of the type universal_integer. See A.5.3.
1. S'Model_Epsilon For every subtype S of a floating point type T:
a. Yields the value T'Machine_Radix ** (1-T'Model_Mantissa). The value
of this attribute is of the type universal_real. See A.5.3.
1. S'Model_Mantissa For every subtype S of a floating point type T:
a. If the Numerics Annex is not supported, this attribute yields an
implementation defined value that is greater than or equal to
Ceiling(d*log (10)/log (T'Machine_Radix))+1, where d is the
requested decimal precision of T, and less than or equal to the
value of T'Machine_Mantissa. See G.2.2 for further requirements that
apply to implementations supporting the Numerics Annex. The value of
this attribute is of the type universal_integer. See A.5.3.
1. S'Model_Small For every subtype S of a floating point type T:
a. Yields the value T'Machine_Radix ** (T'Model_Emin-1). The value of
this attribute is of the type universal_real. See A.5.3.
1. S'Modulus For every modular subtype S:
a. S'Modulus yields the modulus of the type of S, as a value of the
type universal_integer. See 3.5.4.
1. S'Class'Output For every subtype S'Class of a class-wide type T'Class:
a. S'Class'Output denotes a procedure with the following specification:
b.
procedure S'Class'Output
(Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T'Class)
c. First writes the external tag of Item to Stream (by calling
String'Output(Tags.External_Tag(Item'Tag) -- see 3.9.) and then
dispatches to the subprogram denoted by the Output attribute of the
specific type identified by the tag. See 13.13.2.
1. S'Output For every subtype S of a specific type T:
a. S'Output denotes a procedure with the following specification:
b.
procedure S'Output
(Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T)
c. S'Output writes the value of Item to Stream, including any bounds or
discriminants. See 13.13.2.
1. D'Partition_ID For a prefix D that denotes a library-level declaration,
excepting a declaration of or within a declared-pure library unit:
a. Denotes a value of the type universal_integer that identifies the
partition in which D was elaborated. If D denotes the declaration of
a remote call interface library unit, see E.2.3, the given partition
is the one where the body of D was elaborated. See E.1.
1. S'Pos For every discrete subtype S:
a. S'Pos denotes a function with the following specification:
b.
function S'Pos(Arg : S'Base) return universal_integer
c. This function returns the position number of the value of Arg, as a
value of type universal_integer. See 3.5.5.
1. R.C'Position For a component C of a composite, non-array object R:
a. Denotes the same value as R.C'Address - R'Address. The value of this
attribute is of the type universal_integer. See 13.5.2.
1. S'Pred For every scalar subtype S:
a. S'Pred denotes a function with the following specification:
b.
function S'Pred(Arg : S'Base) return S'Base
c. For an enumeration type, the function returns the value whose
position number is one less than that of the value of Arg;
Constraint_Error is raised if there is no such value of the type.
For an integer type, the function returns the result of subtracting
one from the value of Arg. For a fixed point type, the function
returns the result of subtracting small from the value of Arg. For a
floating point type, the function returns the machine number (as
defined in 3.5.7.) immediately below the value of Arg;
Constraint_Error is raised if there is no such machine number. See
3.5.
1. A'Range(N) For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'Range(N) is equivalent to the range A'First(N) ┬╖┬╖ A'Last(N),
except that the prefix A is only evaluated once. See 3.6.2.
1. A'Range For a prefix A that is of an array type (after any implicit
dereference), or denotes a constrained array subtype:
a. A'Range is equivalent to the range A'First ┬╖┬╖ A'Last, except that
the prefix A is only evaluated once. See 3.6.2.
1. S'Range For every scalar subtype S:
a. S'Range is equivalent to the range S'First ┬╖┬╖ S'Last. See 3.5.
1. S'Class'Read For every subtype S'Class of a class-wide type T'Class:
a. S'Class'Read denotes a procedure with the following specification:
b.
procedure S'Class'Read
(Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : out T'Class)
c. Dispatches to the subprogram denoted by the Read attribute of the
specific type identified by the tag of Item. See 13.13.2.
1. S'Read For every subtype S of a specific type T:
a. S'Read denotes a procedure with the following specification:
b.
procedure S'Read
(Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : out T)
c. S'Read reads the value of Item from Stream. See 13.13.2.
1. S'Remainder For every subtype S of a floating point type T:
a. S'Remainder denotes a function with the following specification:
b.
function S'Remainder (X, Y : T) return T
c. For nonzero Y, let v be the value X-n*Y, where n is the integer
nearest to the exact value of X/Y; if |n-X/Y|=1/2, then n is chosen
to be even. If v is a machine number of the type T, the function
yields v; otherwise, it yields zero. Constraint_Error is raised if Y
is zero. A zero result has the sign of X when S'Signed_Zeros is
True. See A.5.3.
1. S'Round For every decimal fixed point subtype S:
a. S'Round denotes a function with the following specification:
b.
function S'Round(X : universal_real) return S'Base
c. The function returns the value obtained by rounding X (away from 0,
if X is midway between two values of the type of S). See 3.5.10.
1. S'Rounding For every subtype S of a floating point type T:
a. S'Rounding denotes a function with the following specification:
b.
function S'Rounding (X : T) return T
c. The function yields the integral value nearest to X, rounding away
from zero if X lies exactly halfway between two integers. A zero
result has the sign of X when S'Signed_Zeros is True. See A.5.3.
1. S'Safe_First For every subtype S of a floating point type T:
a. Yields the lower bound of the safe range, see 3.5.7, of the type T.
If the Numerics Annex is not supported, the value of this attribute
is implementation defined; See G.2.2 for the definition that
applies to implementations supporting the Numerics Annex. The value
of this attribute is of the type universal_real. See A.5.3.
1. S'Safe_Last For every subtype S of a floating point type T:
a. Yields the upper bound of the safe range, see 3.5.7 of the type T.
If the Numerics Annex is not supported, the value of this attribute
is implementation defined; See G.2.2 for the definition that
applies to implementations supporting the Numerics Annex. The value
of this attribute is of the type universal_real. See A.5.3.
1. S'Scale For every decimal fixed point subtype S:
a. S'Scale denotes the scale of the subtype S, defined as the value N
such that S'Delta = 10.0**(-N). The scale indicates the position of
the point relative to the rightmost significant digits of values of
subtype S. The value of this attribute is of the type
universal_integer. See 3.5.10.
1. S'Scaling For every subtype S of a floating point type T:
a. S'Scaling denotes a function with the following specification:
b.
function S'Scaling
(X : T;
Adjustment : universal_integer) return T
c. Let v be the value X*T'Machine_Radix ** Adjustment. If v is a
machine number of the type T, or if |v|>=T'Model_Small, the function
yields v; otherwise, it yields either one of the machine numbers of
the type T adjacent to v. Constraint_Error is optionally raised if v
is outside the base range of S. A zero result has the sign of X when
S'Signed_Zeros is True. See A.5.3.
1. S'Signed_Zeros For every subtype S of a floating point type T:
a. Yields the value True if the hardware representation for the type T
has the capability of representing both positively and negatively
signed zeros, these being generated and used by the predefined
operations of the type T as specified in IEC 559:1989; yields the
value False otherwise. The value of this attribute is of the
predefined type Boolean. See A.5.3.
1. S'Size For every subtype S:
a. If S is definite, denotes the size (in bits) that the implementation
would choose for the following objects of subtype S:
1. A record component of subtype S when the record type is packed.
2. The formal parameter of an instance of Unchecked_Conversion
that converts from subtype S to some other subtype.
a. If S is indefinite, the meaning is implementation defined. The value
of this attribute is of the type universal_integer. See 13.3.
1. X'Size For a prefix X that denotes an object:
a. Denotes the size in bits of the representation of the object. The
value of this attribute is of the type universal_integer. See 13.3.
1. S'Small For every fixed point subtype S:
a. S'Small denotes the small of the type of S. The value of this
attribute is of the type universal_real. See 3.5.10.
1. S'Storage_Pool For every access subtype S:
a. Denotes the storage pool of the type of S. The type of this
attribute is Root_Storage_Pool'Class. See 13.11.
1. S'Storage_Size For every access subtype S:
a. Yields the result of calling Storage_Size(S'Storage_Pool), which is
intended to be a measure of the number of storage elements reserved
for the pool. The type of this attribute is universal_integer. See
13.11.
1. T'Storage_Size For a prefix T that denotes a task object (after any
implicit dereference):
a. Denotes the number of storage elements reserved for the task. The
value of this attribute is of the type universal_integer. The
Storage_Size includes the size of the task's stack, if any. The
language does not specify whether or not it includes other storage
associated with the task (such as the ``task control block'' used by
some implementations.) See 13.3.
1. S'Succ For every scalar subtype S:
a. S'Succ denotes a function with the following specification:
b.
function S'Succ(Arg : S'Base) return S'Base
c. For an enumeration type, the function returns the value whose
position number is one more than that of the value of Arg;
Constraint_Error is raised if there is no such value of the type.
For an integer type, the function returns the result of adding one
to the value of Arg. For a fixed point type, the function returns
the result of adding small to the value of Arg. For a floating point
type, the function returns the machine number (as defined in 3.5.7.)
immediately above the value of Arg; Constraint_Error is raised if
there is no such machine number. See 3.5.
1. S'Tag For every subtype S of a tagged type T (specific or class-wide):
a. S'Tag denotes the tag of the type T (or if T is class-wide, the tag
of the root type of the corresponding class). The value of this
attribute is of type Tag. See 3.9.
1. X'Tag For a prefix X that is of a class-wide tagged type (after any
implicit dereference):
a. X'Tag denotes the tag of X. The value of this attribute is of type
Tag. See 3.9.
1. T'Terminated For a prefix T that is of a task type (after any implicit
dereference):
a. Yields the value True if the task denoted by T is terminated, and
False otherwise. The value of this attribute is of the predefined
type Boolean. See 9.9.
1. S'Truncation For every subtype S of a floating point type T:
a. S'Truncation denotes a function with the following specification:
b.
function S'Truncation (X : T) return T
c. The function yields the value Ceiling(X) when X is negative, and
Floor(X) otherwise. A zero result has the sign of X when
S'Signed_Zeros is True. See A.5.3.
1. S'Unbiased_Rounding For every subtype S of a floating point type T:
a. S'Unbiased_Rounding denotes a function with the following
specification:
b.
function S'Unbiased_Rounding (X : T) return T
c. The function yields the integral value nearest to X, rounding toward
the even integer if X lies exactly halfway between two integers. A
zero result has the sign of X when S'Signed_Zeros is True. See
A.5.3.
1. X'Unchecked_Access For a prefix X that denotes an aliased view of an
object:
a. All rules and semantics that apply to X'Access, see 3.10.2, apply
also to X'Unchecked_Access, except that, for the purposes of
accessibility rules and checks, it is as if X were declared
immediately within a library package. See 13.10.
1. S'Val For every discrete subtype S:
a. S'Val denotes a function with the following specification:
b.
function S'Val(Arg : universal_integer) return S'Base
c. This function returns a value of the type of S whose position number
equals the value of Arg. See 3.5.5.
1. 262 X'Valid For a prefix X that denotes a scalar object (after any
implicit dereference):
a. Yields True if and only if the object denoted by X is normal and has
a valid representation. The value of this attribute is of the
predefined type Boolean. See 13.9.2.
1. S'Value For every scalar subtype S:
a. S'Value denotes a function with the following specification:
b.
function S'Value(Arg : String) return S'Base
c. This function returns a value given an image of the value as a
String, ignoring any leading or trailing spaces. See 3.5.
1. P'Version For a prefix P that statically denotes a program unit:
a. Yields a value of the predefined type String that identifies the
version of the compilation unit that contains the declaration of the
program unit. See E.3.
1. S'Wide_Image For every scalar subtype S:
a. S'Wide_Image denotes a function with the following specification:
b.
function S'Wide_Image(Arg : S'Base) return Wide_String
c. The function returns an image of the value of Arg, that is, a
sequence of characters representing the value in display form. See
3.5.
1. S'Wide_Value For every scalar subtype S:
a. S'Wide_Value denotes a function with the following specification:
b.
function S'Wide_Value(Arg : Wide_String) return S'Base
c. This function returns a value given an image of the value as a
Wide_String, ignoring any leading or trailing spaces. See 3.5.
1. S'Wide_Width For every scalar subtype S:
a. S'Wide_Width denotes the maximum length of a Wide_String returned by
S'Wide_Image over all values of the subtype S. It denotes zero for a
subtype that has a null range. Its type is universal_integer. See
3.5.
1. S'Width For every scalar subtype S:
a. S'Width denotes the maximum length of a String returned by S'Image
over all values of the subtype S. It denotes zero for a subtype that
has a null range. Its type is universal_integer. See 3.5.
1. S'Class'Write For every subtype S'Class of a class-wide type T'Class:
a. S'Class'Write denotes a procedure with the following specification:
b.
procedure S'Class'Write
(Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T'Class)
c. Dispatches to the subprogram denoted by the Write attribute of the
specific type identified by the tag of Item. See 13.13.2.
1. S'Write For every subtype S of a specific type T:
a. S'Write denotes a procedure with the following specification:
b.
procedure S'Write
(Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T)
c. S'Write writes the value of Item to Stream. See 13.13.2.
ΓòÉΓòÉΓòÉ 27. Language-Defined Pragmas (informative) ΓòÉΓòÉΓòÉ
1. This Annex summarizes the definitions given elsewhere of the
language-defined pragmas.
2.
pragma All_Calls_Remote[(library_unit_name)];
-- see E.2.3.
3.
pragma Asynchronous(local_name);
-- see E.4.1.
4.
pragma Atomic(local_name);
-- see C.6.
5.
pragma Atomic_Components(array_local_name);
-- see C.6.
6.
pragma Attach_Handler(handler_name, expression);
-- see C.3.1.
7.
pragma Controlled(first_subtype_local_name);
-- see 13.11.3.
8.
pragma Convention([Convention =>] convention_identifier,
[Entity =>] local_name);
-- see B.1.
9.
pragma Discard_Names[([On => ] local_name)];
-- see C.5.
10.
pragma Elaborate(library_unit_name{, library_unit_name});
-- see 10.2.1.
11.
pragma Elaborate_All(library_unit_name{, library_unit_name});
-- see 10.2.1.
12.
pragma Elaborate_Body[(library_unit_name)];
-- see 10.2.1.
13.
pragma Export( [Convention =>] convention_identifier,
[Entity =>] local_name [, [External_Name =>] string_expression]
[, [Link_Name =>] string_expression]);
-- see B.1.
14.
pragma Import( [Convention =>] convention_identifier,
[Entity =>] local_name [, [External_Name =>] string_expression]
[, [Link_Name =>] string_expression]);
-- see B.1.
15.
pragma Inline(name {, name});
-- see 6.3.2.
16.
pragma Inspection_Point[(object_name {, object_name})];
-- see H.3.2.
17.
pragma Interrupt_Handler(handler_name);
-- see C.3.1.
18.
pragma Interrupt_Priority[(expression)];
-- see D.1.
19.
pragma Linker_Options(string_expression);
-- see B.1.
20.
pragma List(identifier);
-- see 2.8.
21.
pragma Locking_Policy(policy_identifier);
-- see D.3.
22.
pragma Normalize_Scalars;
-- see H.1.
23.
pragma Optimize(identifier);
-- see 2.8.
24.
pragma Pack(first_subtype_local_name);
-- see 13.2.
25.
pragma Page;
-- see 2.8.
26.
pragma Preelaborate[(library_unit_name)];
-- see 10.2.1.
27.
pragma Priority(expression);
-- see D.1.
28.
pragma Pure[(library_unit_name)];
-- see 10.2.1.
29.
pragma Queuing_Policy(policy_identifier);
-- see D.4.
30.
pragma Remote_Call_Interface[(library_unit_name)];
-- see E.2.3.
31.
pragma Remote_Types[(library_unit_name)];
-- see E.2.2.
32.
pragma Restrictions(restriction{, restriction});
-- see 13.12.
33.
pragma Reviewable;
-- see H.3.1.
34.
pragma Shared_Passive[(library_unit_name)];
-- see E.2.1.
35.
pragma Storage_Size(expression);
-- see 13.3.
36.
pragma Suppress(identifier [, [On =>] name]);
-- see 11.5.
37.
pragma Task_Dispatching_Policy(policy_identifier );
-- see D.2.2.
38.
pragma Volatile(local_name);
-- see C.6.
39.
pragma Volatile_Components(array_local_name);
-- see C.6.
ΓòÉΓòÉΓòÉ 28. Implementation-Defined Characteristics (informative) ΓòÉΓòÉΓòÉ
1. The Ada language allows for certain machine dependences in a controlled
manner. Each Ada implementation must document all implementation-defined
characteristics:
a. Whether or not each recommendation given in Implementation Advice is
followed. See 1.1.2(37).
b. Capacity limitations of the implementation. See 1.1.3(3).
c. Variations from the standard that are impractical to avoid given the
implementation's execution environment. See 1.1.3(6).
d. Which code_statements cause external interactions. See 1.1.3(10).
e. The coded representation for the text of an Ada program. See 2.1,
(4).
f. The control functions allowed in comments. See 2.1(14).
g. The representation for an end of line. See 2.2(2).
h. Maximum supported line length and lexical element length. See 2.2,
(15).
i. Implementation-defined pragmas. See 2.8(14).
j. Effect of pragma Optimize. See 2.8(27).
k. The sequence of characters of the value returned by S'Image when
some of the graphic characters of S'Wide_Image are not defined in
Character. See 3.5(37).
l. The predefined integer types declared in Standard. See 3.5.4(25).
m. Any nonstandard integer types and the operators defined for them.
See 3.5.4(26).
n. Any nonstandard real types and the operators defined for them. See
3.5.6(8).
o. What combinations of requested decimal precision and range are
supported for floating point types. See 3.5.7(7).
p. The predefined floating point types declared in Standard. See 3.5.7,
(16).
q. The small of an ordinary fixed point type. See 3.5.9(8).
r. What combinations of small, range, and digits are supported for
fixed point types. See 3.5.9(10).
s. The result of Tags.Expanded_Name for types declared within an
unnamed block_statement. See 3.9(10).
t. Implementation-defined attributes. See 4.1.4(12).
u. Any implementation-defined time types. See 9.6(6).
v. The time base associated with relative delays. See 9.6(20).
w. The time base of the type Calendar.Time. See 9.6(23).
x. The timezone used for package Calendar operations. See 9.6(24).
y. Any limit on delay_until_statements of select_statements. See 9.6,
(29).
z. Whether or not two nonoverlapping parts of a composite object are
independently addressable, in the case where packing, record layout,
or Component_Size is specified for the object. See 9.10(1).
a. The representation for a compilation. See 10.1(2).
b. Any restrictions on compilations that contain multiple
compilation_units. See 10.1(4).
c. The mechanisms for creating an environment and for adding and
replacing compilation units. See 10.1.4(3).
d. The manner of explicitly assigning library units to a partition. See
10.2(2).
e. The implementation-defined means, if any, of specifying which
compilation units are needed by a given compilation unit. See 10.2,
(2).
f. The manner of designating the main subprogram of a partition. See
10.2(7).
g. The order of elaboration of library_items. See 10.2(18).
h. Parameter passing and function return for the main subprogram. See
10.2(21).
i. The mechanisms for building and running partitions. See 10.2(24).
j. The details of program execution, including program termination. See
10.2(25).
k. The semantics of any nonactive partitions supported by the
implementation. See 10.2(28).
l. The information returned by Exception_Message. See 11.4.1(10).
m. The result of Exceptions.Exception_Name for types declared within an
unnamed block_statement. See 11.4.1(12).
n. The information returned by Exception_Information. See 11.4.1(13).
o. Implementation-defined check names. See 11.5(27).
p. The interpretation of each aspect of representation. See 13.1(20).
q. Any restrictions placed upon representation items. See 13.1(20).
r. The meaning of Size for indefinite subtypes. See 13.3(48).
s. The default external representation for a type tag. See 13.3(75).
t. What determines whether a compilation unit is the same in two
different partitions. See 13.3(76).
u. Implementation-defined components. See 13.5.1(15).
v. If Word_Size = Storage_Unit, the default bit ordering. See 13.5.3,
(5).
w. The contents of the visible part of package System and its
language-defined children. See 13.7(2).
x. The contents of the visible part of package System.Machine_Code, and
the meaning of code_statements. See 13.8(7).
y. The effect of unchecked conversion. See 13.9(11).
z. The manner of choosing a storage pool for an access type when
Storage_Pool is not specified for the type. See 13.11(17).
a. Whether or not the implementation provides user-accessible names for
the standard pool type(s). See 13.11(17).
b. The meaning of Storage_Size. See 13.11(18).
c. Implementation-defined aspects of storage pools. See 13.11(22).
d. The set of restrictions allowed in a pragma Restrictions. See 13.12,
(7).
e. The consequences of violating limitations on Restrictions pragmas.
See 13.12(9).
f. The representation used by the Read and Write attributes of
elementary types in terms of stream elements. See 13.13.2(9).
g. The names and characteristics of the numeric subtypes declared in
the visible part of package Standard. See A.1(3).
h. The accuracy actually achieved by the elementary functions. See
A.5.1(1).
i. The sign of a zero result from some of the operators or functions in
Numerics.Generic_Elementary_Functions, when Float_Type'Signed_Zeros
is True. See A.5.1(46).
j. The value of Numerics.Float_Random.Max_Image_Width. See A.5.2(27).
k. The value of Numerics.Discrete_Random.Max_Image_Width. See A.5.2,
(27).
l. The algorithms for random number generation. See See 2(32).
m. The string representation of a random number generator's state. See
A.5.2(38).
n. The minimum time interval between calls to the time-dependent Reset
procedure that are guaranteed to initiate different random number
sequences. See A.5.2(45).
o. The values of the Model_Mantissa, Model_Emin, Model_Epsilon, Model,
Safe_First, and Safe_Last attributes, if the Numerics Annex is not
supported. See A.5.3(72).
p. Any implementation-defined characteristics of the input-output
packages. See A.7(14).
q. The value of Buffer_Size in Storage_IO. See A.9(10).
r. external files for standard input, standard output, and standard
error. See A.10(5).
s. The accuracy of the value produced by Put. See A.10.9(36).
t. The meaning of Argument_Count, Argument, and Command_Name. See A.15,
(1).
u. Implementation-defined convention names. See B.1(11).
v. The meaning of link names. See B.1(36).
w. The manner of choosing link names when neither the link name nor the
address of an imported or exported entity is specified. See B.1,
(36).
x. The effect of pragma Linker_Options. See B.1(37).
y. The contents of the visible part of package Interfaces and its
language-defined descendants. See B.2(1).
z. Implementation-defined children of package Interfaces. The contents
of the visible part of package Interfaces. See 11.
a. The types Floating, Long_Floating, Binary, Long_Binary,
Decimal_Element, and COBOL_Character; and the initializations of the
variables Ada_To_COBOL and COBOL_To_Ada, in Interfaces.COBOL See
B.4(50).
b. Support for access to machine instructions. See C.1(1).
c. Implementation-defined aspects of access to machine operations. See
C.1(9).
d. Implementation-defined aspects of interrupts. See C.3(2).
e. Implementation-defined aspects of preelaboration. See C.4(13).
f. The semantics of pragma Discard_Names. See C.5(7).
g. The result of the Task_Identification.Image attribute. See C.7.1,
(7).
h. The value of Current_Task when in a protected entry or interrupt
handler. See C.7.1(17).
i. The effect of calling Current_Task from an entry body or interrupt
handler. See C.7.1(19).
j. Implementation-defined aspects of Task_Attributes. See C.7.2(19).
k. Values of all Metrics. See D(2).
l. The declarations of Any_Priority and Priority. See D.1(11).
m. Implementation-defined execution resources. See D.1(15).
n. Whether, on a multiprocessor, a task that is waiting for access to a
protected object keeps its processor busy. See D.2.1(3).
o. The affect of implementation defined execution resources on task
dispatching. See D.2.1(9).
p. Implementation-defined policy_identifiers allowed in a pragma
Task_Dispatching_Policy. See D.2.2(3).
q. Implementation-defined aspects of priority inversion. See D.2.2,
(16).
r. Implementation defined task dispatching. See D.2.2(18).
s. Implementation-defined policy_identifiers allowed in a pragma
Locking_Policy. See D.3(4).
t. Default ceiling priorities. See D.3(10).
u. The ceiling of any protected object used internally by the
implementation. See D.3(16).
v. Implementation-defined queuing policies. See D.4(1).
w. On a multiprocessor, any conditions that cause the completion of an
aborted construct to be delayed later than what is specified for a
single processor. See D.6(3).
x. Any operations that implicitly require heap storage allocation. See
D.7(8).
y. Implementation-defined aspects of pragma Restrictions. See D.7(20).
z. Implementation-defined aspects of package Real_Time. See D.8(17).
a. Implementation-defined aspects of delay_statements. See D.9(8).
b. The upper bound on the duration of interrupt blocking caused by the
implementation. See D.12(5).
c. The means for creating and executing distributed programs. See E,
(5).
d. Any events that can result in a partition becoming inaccessible. See
E.1(7).
e. The scheduling policies, treatment of priorities, and management of
shared resources between partitions in certain cases. See E.1(11).
f. Events that cause the version of a compilation unit to change. See
E.3(5).
g. Whether the execution of the remote subprogram is immediately
aborted as a result of cancellation. See E.4(13).
h. Implementation-defined aspects of the PCS. See E.5(25).
i. Implementation-defined interfaces in the PCS. See E.5(26).
j. The values of named numbers in the package Decimal. See F.2(7).
k. The value of Max_Picture_Length in the package Text_IO.Editing See
F.3.3(16).
l. The value of Max_Picture_Length in the package Wide_Text_IO.Editing
See F.3.4(5).
m. The accuracy actually achieved by the complex elementary functions
and by other complex arithmetic operations. See G.1(1).
n. The sign of a zero result (or a component thereof) from any operator
or function in Numerics.Generic_Complex_Types, when
Real'Signed_Zeros is True. See G.1.1(53).
o. The sign of a zero result (or a component thereof) from any operator
or function in Numerics.Generic_Complex_Elementary_Functions, when
Complex_Types.Real'Signed_Zeros is True. See G.1.2(45).
p. Whether the strict mode or the relaxed mode is the default. See G.2,
(2).
q. The result interval in certain cases of fixed-to-float conversion.
See G.2.1(10).
r. The result of a floating point arithmetic operation in overflow
situations, when the Machine_Overflows attribute of the result type
is False. See G.2.1(13).
s. The result interval for division (or exponentiation by a negative
exponent), when the floating point hardware implements division as
multiplication by a reciprocal. See G.2.1(16).
t. The definition of close result set, which determines the accuracy of
certain fixed point multiplications and divisions. See G.2.3(5).
u. Conditions on a universal_real operand of a fixed point
multiplication or division for which the result shall be in the
perfect result set. See G.2.3(22).
v. The result of a fixed point arithmetic operation in overflow
situations, when the Machine_Overflows attribute of the result type
is False. See G.2.3(27).
w. The result of an elementary function reference in overflow
situations, when the Machine_Overflows attribute of the result type
is False. See G.2.4(4).
x. The value of the angle threshold, within which certain elementary
functions, complex arithmetic operations, and complex elementary
functions yield results conforming to a maximum relative error
bound. See G.2.4(10).
y. The accuracy of certain elementary functions for parameters beyond
the angle threshold. See G.2.4(10).
z. The result of a complex arithmetic operation or complex elementary
function reference in overflow situations, when the
Machine_Overflows attribute of the corresponding real type is False.
See G.2.6(5).
a. The accuracy of certain complex arithmetic operations and certain
complex elementary functions for parameters (or components thereof)
beyond the angle threshold. See G.2.6(8).
b. Information regarding bounded errors and erroneous execution. See
H.2(1).
c. Implementation-defined aspects of pragma Inspection_Point. See
H.3.2, (8).
d. Implementation-defined aspects of pragma Restrictions. See H.4(25).
e. Any restrictions on pragma Restrictions. See H.4(27).
ΓòÉΓòÉΓòÉ 29. Glossary (informative) ΓòÉΓòÉΓòÉ
1. This Annex contains informal descriptions of some terms used in this
International Standard. To find more formal definitions, look the term up
in the index.
2. Access type. An access type has values that designate aliased objects.
Access types correspond to ``pointer types'' or ``reference types'' in
some other languages.
3. Aliased. An aliased view of an object is one that can be designated by an
access value. Objects allocated by allocators are aliased. Objects can
also be explicitly declared as aliased with the reserved word aliased.
The Access attribute can be used to create an access value designating an
aliased object.
4. Array type. An array type is a composite type whose components are all of
the same type. Components are selected by indexing.
5. Character type. A character type is an enumeration type whose values
include characters.
6. Class. A class is a set of types that is closed under derivation, which
means that if a given type is in the class, then all types derived from
that type are also in the class. The set of types of a class share common
properties, such as their primitive operations.
7. Compilation unit. The text of a program can be submitted to the compiler
in one or more compilations. Each compilation is a succession of
compilation_units. A compilation_unit contains either the declaration,
the body, or a renaming of a program unit.
8. Composite type. A composite type has components.
9. Construct. A construct is a piece of text (explicit or implicit) that is
an instance of a syntactic category defined under ``Syntax.''
10. Controlled type. A controlled type supports user-defined assignment and
finalization. Objects are always finalized before being destroyed.
Declaration. A declaration is a language construct that associates a name
with (a view of) an entity. A declaration may appear explicitly in the
program text (an explicit declaration), or may be supposed to occur at a
given place in the text as a consequence of the semantics of another
construct (an implicit declaration).
11. Definition. All declarations contain a definition for a view of an
entity. A view consists of an identification of the entity (the entity of
the view), plus view-specific characteristics that affect the use of the
entity through that view (such as mode of access to an object, formal
parameter names and defaults for a subprogram, or visibility to
components of a type). In most cases, a declaration also contains the
definition for the entity itself (a renaming_declaration is an example of
a declaration that does not define a new entity, but instead defines a
view of an existing entity, see 8.5.
12. Derived type. A derived type is a type defined in terms of another type,
which is the parent type of the derived type. Each class containing the
parent type also contains the derived type. The derived type inherits
properties such as components and primitive operations from the parent. A
type together with the types derived from it (directly or indirectly)
form a derivation class.
13. Discrete type. A discrete type is either an integer type or an
enumeration type. Discrete types may be used, for example, in
case_statements and as array indices.
14. Discriminant. A discriminant is a parameter of a composite type. It can
control, for example, the bounds of a component of the type if that type
is an array type. A discriminant of a task type can be used to pass data
to a task of the type upon creation.
15. Elementary type. An elementary type does not have components.
16. Enumeration type. An enumeration type is defined by an enumeration of its
values, which may be named by identifiers or character literals.
17. Exception. An exception represents a kind of exceptional situation; an
occurrence of such a situation (at run time) is called an exception
occurrence. To raise an exception is to abandon normal program execution
so as to draw attention to the fact that the corresponding situation has
arisen. Performing some actions in response to the arising of an
exception is called handling the exception.
18. Execution. The process by which a construct achieves its run-time effect
is called execution. Execution of a declaration is also called
elaboration. Execution of an expression is also called evaluation.
19. Generic unit. A generic unit is a template for a (nongeneric) program
unit; the template can be parameterized by objects, types, subprograms,
and packages. An instance of a generic unit is created by a
generic_instantiation. The rules of the language are enforced when a
generic unit is compiled, using a generic contract model; additional
checks are performed upon instantiation to verify the contract is met.
That is, the declaration of a generic unit represents a contract between
the body of the generic and instances of the generic. Generic units can
be used to perform the role that macros sometimed play in other
languages.
20. Integer type. Integer types comprise the signed integer types and the
modular types. A signed integer type has a base range that includes both
positive and negative numbers, and has operations that may raise an
exception when the result is outside the base range. A modular type has a
base range whose lower bound is zero, and has operations with
``wraparound'' semantics. Modular types subsume what are called
``unsigned types'' in some other languages.
21. Library unit. A library unit is a separately compiled program unit, and
is always a package, subprogram, or generic unit. Library units may have
other (logically nested) library units as children, and may have other
program units physically nested within them. A root library unit,
together with its children and grandchildren and so on, form a subsystem.
22. Limited type. A limited type is (a view of) a type for which the
assignment operation is not allowed. A nonlimited type is a (view of a)
type for which the assignment operation is allowed.
23. Object. An object is either a constant or a variable. An object contains
a value. An object is created by an object_declaration or by an
allocator. A formal parameter is (a view of) an object. A subcomponent of
an object is an object.
24. Package. Packages are program units that allow the specification of
groups of logically related entities. Typically, a package contains the
declaration of a type (often a private type or private extension) along
with the declarations of primitive subprograms of the type, which can be
called from outside the package, while their inner workings remain hidden
from outside users.
25. Partition. A partition is a part of a program. Each partition consists of
a set of library units. Each partition may run in a separate address
space, possibly on a separate computer. A program may contain just one
partition. A distributed program typically contains multiple partitions,
which can execute concurrently.
26. Pragma. A pragma is a compiler directive. There are language-defined
pragmas that give instructions for optimization, listing control, etc. An
implementation may support additional (implementation-defined) pragmas.
27. Primitive operations. The primitive operations of a type are the
operations (such as subprograms) declared together with the type
declaration. They are inherited by other types in the same class of
types. For a tagged type, the primitive subprograms are dispatching
subprograms, providing run-time polymorphism. A dispatching subprogram
may be called with statically tagged operands, in which case the
subprogram body invoked is determined at compile time. Alternatively, a
dispatching subprogram may be called using a dispatching call, in which
case the subprogram body invoked is determined at run time.
28. Private extension. A private extension is like a record extension, except
that the components of the extension part are hidden from its clients.
29. Private type. A private type is a partial view of a type whose full view
is hidden from its clients.
30. Program unit. A program unit is either a package, a task unit, a
protected unit, a protected entry, a generic unit, or an explicitly
declared subprogram other than an enumeration literal. Certain kinds of
program units can be separately compiled. Alternatively, they can appear
physically nested within other program units.
31. Program. A program is a set of partitions, each of which may execute in a
separate address space, possibly on a separate computer. A partition
consists of a set of library units.
32. Protected type. A protected type is a composite type whose components are
protected from concurrent access by multiple tasks.
33. Real type. A real type has values that are approximations of the real
numbers. Floating point and fixed point types are real types.
34. Record extension. A record extension is a type that extends another type
by adding additional components.
35. Record type. A record type is a composite type consisting of zero or more
named components, possibly of different types.
36. Scalar type. A scalar type is either a discrete type or a real type.
37. Subtype. A subtype is a type together with a constraint, which constrains
the values of the subtype to satisfy a certain condition. The values of a
subtype are a subset of the values of its type.
38. Tagged type. The objects of a tagged type have a run-time type tag, which
indicates the specific type with which the object was originally created.
An operand of a class-wide tagged type can be used in a dispatching call;
the tag indicates which subprogram body to invoke. Nondispatching calls,
in which the subprogram body to invoke is determined at compile time, are
also allowed. Tagged types may be extended with additional components.
39. Task type. A task type is a composite type whose values are tasks, which
are active entities that may execute concurrently with other tasks. The
top-level task of a partition is called the environment task.
40. Type. Each object has a type. A type has an associated set of values, and
a set of primitive operations which implement the fundamental aspects of
its semantics. Types are grouped into classes. The types of a given class
share a set of primitive operations. Classes are closed under derivation;
that is, if a type is in a class, then all of its derivatives are in that
class.
41. View. (See Definition.)
ΓòÉΓòÉΓòÉ 30. Syntax Summary (informative) ΓòÉΓòÉΓòÉ
1. This Annex summarizes the complete syntax of the language. 1.1.4, for a
description of the notation used.
2.1
character ::=
graphic_character
| format_effector
| other_control_function
2.1
graphic_character ::=
identifier_letter
| digit
| space_character
| special_character
2.3
identifier ::= identifier_letter {[underline] letter_or_digit}
2.3
letter_or_digit ::= identifier_letter | digit
2.4
numeric_literal ::= decimal_literal | based_literal
2.4.1
decimal_literal ::= numeral [.numeral] [exponent]
2.4.1
numeral ::= digit {[underline] digit}
2.4.1
exponent ::= E [+] numeral | E - numeral
2.4.2
based_literal ::= base # based_numeral [.based_numeral] # [exponent]
2.4.2
base ::= numeral
2.4.2
based_numeral ::= extended_digit {[underline] extended_digit}
2.4.2
extended_digit ::= digit | A | B | C | D | E | F
2.5
character_literal ::= 'graphic_character'
2.6
string_literal ::= "{string_element}"
2.6
string_element ::= "" | non_quotation_mark_graphic_character
A string_element is either a pair of quotation marks (""), or a
single graphic_character other than a quotation mark.
2.7
comment ::= --{non_end_of_line_character}
2.8
pragma ::=
pragma identifier [(pragma_argument_association
{, pragma_argument_association})];
2.8
pragma_argument_association ::=
[pragma_argument_identifier =>] name
| [pragma_argument_identifier =>] expression
3.1
basic_declaration ::=
type_declaration | subtype_declaration
| object_declaration | number_declaration
| subprogram_declaration | abstract_subprogram_declaration
| package_declaration | renaming_declaration
| exception_declaration | generic_declaration
| generic_instantiation
3.1
defining_identifier ::= identifier
3.2.1
type_declaration ::=
full_type_declaration
| incomplete_type_declaration
| private_type_declaration
| private_extension_declaration
3.2.1
full_type_declaration ::=
type defining_identifier [known_discriminant_part]
is type_definition;
| task_type_declaration
| protected_type_declaration
3.2.1
type_definition ::=
enumeration_type_definition | integer_type_definition
| real_type_definition | array_type_definition
| record_type_definition | access_type_definition
| derived_type_definition
3.2.2
subtype_declaration ::=
subtype defining_identifier is subtype_indication;
3.2.2
subtype_indication ::= subtype_mark [constraint]
3.2.2
subtype_mark ::= subtype_name
3.2.2
constraint ::= scalar_constraint | composite_constraint
3.2.2
scalar_constraint ::=
range_constraint | digits_constraint | delta_constraint
3.2.2
composite_constraint ::=
index_constraint | discriminant_constraint
3.3.1
object_declaration ::=
defining_identifier_list : [aliased] [constant]
subtype_indication [:= expression];
| defining_identifier_list : [aliased] [constant]
array_type_definition [:= expression];
| single_task_declaration
| single_protected_declaration
3.3.1
defining_identifier_list ::=
defining_identifier {, defining_identifier}
3.3.2
number_declaration ::=
defining_identifier_list : constant := static_expression;
3.4
derived_type_definition ::= [abstract] new
parent_subtype_indication [record_extension_part]
3.5
range_constraint ::= range range
3.5
range ::=
range_attribute_reference
| simple_expression ┬╖┬╖ simple_expression
3.5.1
enumeration_type_definition ::=
(enumeration_literal_specification
{, enumeration_literal_specification})
3.5.1
enumeration_literal_specification ::=
defining_identifier | defining_character_literal
3.5.1
defining_character_literal ::= character_literal
3.5.4
integer_type_definition ::=
signed_integer_type_definition | modular_type_definition
3.5.4
signed_integer_type_definition ::=
range static_simple_expression ┬╖┬╖ static_simple_expression
3.5.4
modular_type_definition ::= mod static_expression
3.5.6
real_type_definition ::=
floating_point_definition | fixed_point_definition
3.5.7
floating_point_definition ::=
digits static_expression [real_range_specification]
3.5.7
real_range_specification ::=
range static_simple_expression ┬╖┬╖ static_simple_expression
3.5.9
fixed_point_definition ::=
ordinary_fixed_point_definition | decimal_fixed_point_definition
3.5.9
ordinary_fixed_point_definition ::=
delta static_expression real_range_specification
3.5.9
decimal_fixed_point_definition ::=
delta static_expression digits static_expression
[real_range_specification]
3.5.9
digits_constraint ::=
digits static_expression [range_constraint]
3.6
array_type_definition ::=
unconstrained_array_definition | constrained_array_definition
3.6
unconstrained_array_definition ::=
array(index_subtype_definition {, index_subtype_definition})
of component_definition
3.6
index_subtype_definition ::= subtype_mark range <>
3.6
constrained_array_definition ::=
array (discrete_subtype_definition
{, discrete_subtype_definition}) of component_definition
3.6
discrete_subtype_definition ::= discrete_subtype_indication | range
3.6
component_definition ::= [aliased] subtype_indication
3.6.1
index_constraint ::= (discrete_range {, discrete_range})
3.6.1
discrete_range ::= discrete_subtype_indication | range
3.7
discriminant_part ::=
unknown_discriminant_part | known_discriminant_part
3.7
unknown_discriminant_part ::= (<>)
3.7
known_discriminant_part ::=
(discriminant_specification {; discriminant_specification})
3.7
discriminant_specification ::=
defining_identifier_list : subtype_mark
[:= default_expression]
| defining_identifier_list : access_definition
[:= default_expression]
3.7
default_expression ::= expression
3.7.1
discriminant_constraint ::=
(discriminant_association {, discriminant_association})
3.7.1
discriminant_association ::=
[discriminant_selector_name
{| discriminant_selector_name} =>] expression
3.8
record_type_definition ::=
[[abstract] tagged] [limited] record_definition
3.8
record_definition ::=
record
component_list
end record
| null record
3.8
component_list ::=
component_item {component_item}
| {component_item} variant_part
| null;
3.8
component_item ::= component_declaration | representation_clause
3.8
component_declaration ::=
defining_identifier_list : component_definition
[:= default_expression];
3.8.1
variant_part ::=
case discriminant_direct_name is
variant
{variant}
end case;
3.8.1
variant ::=
when discrete_choice_list =>
component_list
3.8.1
discrete_choice_list ::= discrete_choice {| discrete_choice}
3.8.1
discrete_choice ::= expression | discrete_range | others
3.9.1
record_extension_part ::= with record_definition
3.10
access_type_definition ::=
access_to_object_definition
| access_to_subprogram_definition
3.10
access_to_object_definition ::=
access [general_access_modifier] subtype_indication
3.10
general_access_modifier ::= all | constant
3.10
access_to_subprogram_definition ::=
access [protected] procedure parameter_profile
| access [protected] function parameter_and_result_profile
3.10
access_definition ::= access subtype_mark
3.10.1
incomplete_type_declaration ::=
type defining_identifier [discriminant_part];
3.11
declarative_part ::= {declarative_item}
3.11
declarative_item ::= basic_declarative_item | body
3.11
basic_declarative_item ::=
basic_declaration | representation_clause | use_clause
3.11
body ::= proper_body | body_stub
3.11
proper_body ::=
subprogram_body | package_body | task_body | protected_body
4.1
name ::=
direct_name | explicit_dereference
| indexed_component | slice
| selected_component | attribute_reference
| type_conversion | function_call
| character_literal
4.1
direct_name ::= identifier | operator_symbol
4.1
prefix ::= name | implicit_dereference
4.1
explicit_dereference ::= name.all
4.1
implicit_dereference ::= name
4.1.1
indexed_component ::= prefix(expression {, expression})
4.1.2
slice ::= prefix(discrete_range)
4.1.3
selected_component ::= prefix . selector_name
4.1.3
selector_name ::= identifier | character_literal | operator_symbol
4.1.4
attribute_reference ::= prefix'attribute_designator
4.1.4
attribute_designator ::=
identifier[(static_expression)]
| Access | Delta | Digits
4.1.4
range_attribute_reference ::= prefix'range_attribute_designator
4.1.4
range_attribute_designator ::= Range[(static_expression)]
4.3
aggregate ::=
record_aggregate | extension_aggregate | array_aggregate
4.3.1
record_aggregate ::= (record_component_association_list)
4.3.1
record_component_association_list ::=
record_component_association {, record_component_association}
| null record
4.3.1
record_component_association ::=
[ component_choice_list => ] expression
4.3.1
component_choice_list ::=
component_selector_name {| component_selector_name}
| others
4.3.2
extension_aggregate ::=
(ancestor_part with record_component_association_list)
4.3.2
ancestor_part ::= expression | subtype_mark
4.3.3
array_aggregate ::=
positional_array_aggregate | named_array_aggregate
4.3.3
positional_array_aggregate ::=
(expression, expression {, expression})
| (expression {, expression}, others => expression)
4.3.3
named_array_aggregate ::=
(array_component_association {, array_component_association})
4.3.3
array_component_association ::=
discrete_choice_list => expression
4.4
expression ::=
relation {and relation} | relation {and then relation}
| relation {or relation} | relation {or else relation}
| relation {xor relation}
4.4
relation ::=
simple_expression [relational_operator simple_expression]
| simple_expression [not] in range
| simple_expression [not] in subtype_mark
4.4
simple_expression ::=
[unary_adding_operator] term {binary_adding_operator term}
4.4
term ::= factor {multiplying_operator factor}
4.4
factor ::= primary [** primary] | abs primary | not primary
4.4
primary ::=
numeric_literal | null
| string_literal | aggregate
| name | qualified_expression
| allocator | (expression)
4.5
logical_operator ::= and | or | xor
4.5
relational_operator ::= = | /= | < | <= | > | >=
4.5
binary_adding_operator ::= + | - | &
4.5
unary_adding_operator ::= + | -
4.5
multiplying_operator ::= * | / | mod | rem
4.5
highest_precedence_operator ::= ** | abs | not
4.6
type_conversion ::=
subtype_mark(expression)
| subtype_mark(name)
4.7
qualified_expression ::=
subtype_mark'(expression) | subtype_mark'aggregate
4.8
allocator ::=
new subtype_indication | new qualified_expression
5.1
sequence_of_statements ::= statement {statement}
5.1
statement ::=
{label} simple_statement | {label} compound_statement
5.1
simple_statement ::= null_statement
| assignment_statement | exit_statement
| goto_statement | procedure_call_statement
| return_statement | entry_call_statement
| requeue_statement | delay_statement
| abort_statement | raise_statement
| code_statement
5.1
compound_statement ::=
if_statement | case_statement
| loop_statement | block_statement
| accept_statement | select_statement
5.1
null_statement ::= null;
5.1
label ::= <<label_statement_identifier>>
5.1
statement_identifier ::= direct_name
5.2
assignment_statement ::= variable_name := expression;
5.3
if_statement ::=
if condition then
sequence_of_statements
{elsif condition then
sequence_of_statements}
[else
sequence_of_statements]
end if;
5.3
condition ::= boolean_expression
5.4
case_statement ::=
case expression is
case_statement_alternative
{case_statement_alternative}
end case;
5.4
case_statement_alternative ::=
when discrete_choice_list =>
sequence_of_statements
5.5
loop_statement ::=
[loop_statement_identifier:]
[iteration_scheme] loop
sequence_of_statements
end loop [loop_identifier];
5.5
iteration_scheme ::= while condition
| for loop_parameter_specification
5.5
loop_parameter_specification ::=
defining_identifier in [reverse] discrete_subtype_definition
5.6
block_statement ::=
[block_statement_identifier:]
[declare
declarative_part]
begin
handled_sequence_of_statements
end [block_identifier];
5.7
exit_statement ::= exit [loop_name] [when condition];
5.8
goto_statement ::= goto label_name;
6.1
subprogram_declaration ::= subprogram_specification;
6.1
abstract_subprogram_declaration ::= subprogram_specification is abstract;
6.1
subprogram_specification ::=
procedure defining_program_unit_name parameter_profile
| function defining_designator parameter_and_result_profile
6.1
designator ::= [parent_unit_name . ]identifier | operator_symbol
6.1
defining_designator ::=
defining_program_unit_name | defining_operator_symbol
6.1
defining_program_unit_name ::=
[parent_unit_name . ]defining_identifier
6.1
operator_symbol ::= string_literal
6.1
defining_operator_symbol ::= operator_symbol
6.1
parameter_profile ::= [formal_part]
6.1
parameter_and_result_profile ::= [formal_part] return subtype_mark
6.1
formal_part ::=
(parameter_specification {; parameter_specification})
6.1
parameter_specification ::=
defining_identifier_list : mode subtype_mark
[:= default_expression]
| defining_identifier_list : access_definition
[:= default_expression]
6.1
mode ::= [in] | in out | out
6.3
subprogram_body ::=
subprogram_specification is
declarative_part
begin
handled_sequence_of_statements
end [designator];
6.4
procedure_call_statement ::=
procedure_name;
| procedure_prefix actual_parameter_part;
6.4
function_call ::=
function_name
| function_prefix actual_parameter_part
6.4
actual_parameter_part ::=
(parameter_association {, parameter_association})
6.4
parameter_association ::=
[formal_parameter_selector_name =>] explicit_actual_parameter
6.4
explicit_actual_parameter ::= expression | variable_name
6.5
return_statement ::= return [expression];
7.1
package_declaration ::= package_specification;
7.1
package_specification ::=
package defining_program_unit_name is
{basic_declarative_item}
[private
{basic_declarative_item}]
end [[parent_unit_name.]identifier]
7.2
package_body ::=
package body defining_program_unit_name is
declarative_part
[begin
handled_sequence_of_statements]
end [[parent_unit_name.]identifier];
7.3
private_type_declaration ::=
type defining_identifier [discriminant_part] is
[[abstract] tagged] [limited] private;
7.3
private_extension_declaration ::=
type defining_identifier [discriminant_part] is
[abstract] new ancestor_subtype_indication with private;
8.4
use_clause ::= use_package_clause | use_type_clause
8.4
use_package_clause ::= use package_name {, package_name};
8.4
use_type_clause ::= use type subtype_mark {, subtype_mark};
8.5
renaming_declaration ::=
object_renaming_declaration
| exception_renaming_declaration
| package_renaming_declaration
| subprogram_renaming_declaration
| generic_renaming_declaration
8.5.1
object_renaming_declaration ::=
defining_identifier : subtype_mark renames object_name;
8.5.2
exception_renaming_declaration ::=
defining_identifier : exception renames exception_name;
8.5.3
package_renaming_declaration ::=
package defining_program_unit_name renames package_name;
8.5.4
subprogram_renaming_declaration ::=
subprogram_specification renames callable_entity_name;
8.5.5
generic_renaming_declaration ::=
generic package defining_program_unit_name renames
generic_package_name;
| generic procedure defining_program_unit_name renames
generic_procedure_name;
| generic function defining_program_unit_name renames
generic_function_name;
9.1
task_type_declaration ::=
task type defining_identifier [known_discriminant_part]
[is task_definition];
9.1
single_task_declaration ::=
task defining_identifier [is task_definition];
9.1
task_definition ::=
{task_item}
[ private
{task_item}]
end [task_identifier]
9.1
task_item ::= entry_declaration | representation_clause
9.1
task_body ::=
task body defining_identifier is
declarative_part
begin
handled_sequence_of_statements
end [task_identifier];
9.4
protected_type_declaration ::=
protected type defining_identifier [known_discriminant_part] is
protected_definition;
9.4
single_protected_declaration ::=
protected defining_identifier is protected_definition;
9.4
protected_definition ::=
{ protected_operation_declaration }
[ private
{ protected_element_declaration } ]
end [protected_identifier]
9.4
protected_operation_declaration ::=
subprogram_declaration
| entry_declaration
| representation_clause
9.4
protected_element_declaration ::=
protected_operation_declaration | component_declaration
9.4
protected_body ::=
protected body defining_identifier is
{ protected_operation_item }
end [protected_identifier];
9.4
protected_operation_item ::=
subprogram_declaration
| subprogram_body
| entry_body
| representation_clause
9.5.2
entry_declaration ::=
entry defining_identifier [(discrete_subtype_definition)]
parameter_profile;
9.5.2
accept_statement ::=
accept entry_direct_name [(entry_index)] parameter_profile [do
handled_sequence_of_statements
end [entry_identifier]];
9.5.2
entry_index ::= expression
9.5.2
entry_body ::=
entry defining_identifier entry_body_formal_part entry_barrier is
declarative_part
begin
handled_sequence_of_statements
end [entry_identifier];
9.5.2
entry_body_formal_part ::=
[(entry_index_specification)] parameter_profile
9.5.2
entry_barrier ::= when condition
9.5.2
entry_index_specification ::=
for defining_identifier in discrete_subtype_definition
9.5.3
entry_call_statement ::= entry_name [actual_parameter_part];
9.5.4
requeue_statement ::= requeue entry_name [with abort];
9.6
delay_statement ::= delay_until_statement | delay_relative_statement
9.6
delay_until_statement ::= delay until delay_expression;
9.6
delay_relative_statement ::= delay delay_expression;
9.7
select_statement ::=
selective_accept
| timed_entry_call
| conditional_entry_call
| asynchronous_select
9.7.1
selective_accept ::=
select
[guard]
select_alternative
{ or
[guard]
select_alternative }
[ else
sequence_of_statements ]
end select;
9.7.1
guard ::= when condition =>
9.7.1
select_alternative ::=
accept_alternative
| delay_alternative
| terminate_alternative
9.7.1
accept_alternative ::=
accept_statement [sequence_of_statements]
9.7.1
delay_alternative ::=
delay_statement [sequence_of_statements]
9.7.1
terminate_alternative ::= terminate;
9.7.2
timed_entry_call ::=
select
entry_call_alternative
or
delay_alternative
end select;
9.7.2
entry_call_alternative ::=
entry_call_statement [sequence_of_statements]
9.7.3
conditional_entry_call ::=
select
entry_call_alternative
else
sequence_of_statements
end select;
9.7.4
asynchronous_select ::=
select
triggering_alternative
then abort
abortable_part
end select;
9.7.4
triggering_alternative ::=
triggering_statement [sequence_of_statements]
9.7.4
triggering_statement ::= entry_call_statement | delay_statement
9.7.4
abortable_part ::= sequence_of_statements
9.8
abort_statement ::= abort task_name {, task_name};
10.1.1
compilation ::= {compilation_unit}
10.1.1
compilation_unit ::=
context_clause library_item
| context_clause subunit
10.1.1
library_item ::= [private] library_unit_declaration
| library_unit_body
| [private] library_unit_renaming_declaration
10.1.1
library_unit_declaration ::=
subprogram_declaration | package_declaration
| generic_declaration | generic_instantiation
10.1.1
library_unit_renaming_declaration ::=
package_renaming_declaration
| generic_renaming_declaration
| subprogram_renaming_declaration
10.1.1
library_unit_body ::= subprogram_body | package_body
10.1.1
parent_unit_name ::= name
10.1.2
context_clause ::= {context_item}
10.1.2
context_item ::= with_clause | use_clause
10.1.2
with_clause ::= with library_unit_name {, library_unit_name};
10.1.3
body_stub ::=
subprogram_body_stub
| package_body_stub
| task_body_stub
| protected_body_stub
10.1.3
subprogram_body_stub ::= subprogram_specification is separate;
10.1.3
package_body_stub ::= package body defining_identifier is separate;
10.1.3
task_body_stub ::= task body defining_identifier is separate;
10.1.3
protected_body_stub ::=
protected body defining_identifier is separate;
10.1.3
subunit ::= separate (parent_unit_name) proper_body
11.1
exception_declaration ::= defining_identifier_list : exception;
11.2
handled_sequence_of_statements ::=
sequence_of_statements
[exception
exception_handler
{exception_handler}]
11.2
exception_handler ::=
when [choice_parameter_specification:] exception_choice
{| exception_choice} =>
sequence_of_statements
11.2
choice_parameter_specification ::= defining_identifier
11.2
exception_choice ::= exception_name | others
11.3
raise_statement ::= raise [exception_name];
12.1
generic_declaration ::=
generic_subprogram_declaration | generic_package_declaration
12.1
generic_subprogram_declaration ::=
generic_formal_part subprogram_specification;
12.1
generic_package_declaration ::=
generic_formal_part package_specification;
12.1
generic_formal_part ::=
generic {generic_formal_parameter_declaration | use_clause}
12.1
generic_formal_parameter_declaration ::=
formal_object_declaration
| formal_type_declaration
| formal_subprogram_declaration
| formal_package_declaration
12.3
generic_instantiation ::=
package defining_program_unit_name is
new generic_package_name [generic_actual_part];
| procedure defining_program_unit_name is
new generic_procedure_name [generic_actual_part];
| function defining_designator is
new generic_function_name [generic_actual_part];
12.3
generic_actual_part ::=
(generic_association {, generic_association})
12.3
generic_association ::=
[generic_formal_parameter_selector_name =>]
explicit_generic_actual_parameter
12.3
explicit_generic_actual_parameter ::= expression | variable_name
| subprogram_name | entry_name | subtype_mark
| package_instance_name
12.4
formal_object_declaration ::=
defining_identifier_list : mode subtype_mark
[:= default_expression];
12.5
formal_type_declaration ::=
type defining_identifier[discriminant_part] is
formal_type_definition;
12.5
formal_type_definition ::=
formal_private_type_definition
| formal_derived_type_definition
| formal_discrete_type_definition
| formal_signed_integer_type_definition
| formal_modular_type_definition
| formal_floating_point_definition
| formal_ordinary_fixed_point_definition
| formal_decimal_fixed_point_definition
| formal_array_type_definition
| formal_access_type_definition
12.5.1
formal_private_type_definition ::=
[[abstract] tagged] [limited] private
12.5.1
formal_derived_type_definition ::=
[abstract] new subtype_mark [with private]
12.5.2
formal_discrete_type_definition ::= (<>)
12.5.2
formal_signed_integer_type_definition ::= range <>
12.5.2
formal_modular_type_definition ::= mod <>
12.5.2
formal_floating_point_definition ::= digits <>
12.5.2
formal_ordinary_fixed_point_definition ::= delta <>
12.5.2
formal_decimal_fixed_point_definition ::= delta <> digits <>
12.5.3
formal_array_type_definition ::= array_type_definition
12.5.4
formal_access_type_definition ::= access_type_definition
12.6
formal_subprogram_declaration ::=
with subprogram_specification [is subprogram_default];
12.6
subprogram_default ::= default_name | <>
12.6
default_name ::= name
12.7
formal_package_declaration ::=
with package defining_identifier is new
generic_package_name formal_package_actual_part;
12.7
formal_package_actual_part ::= (<>) | [generic_actual_part]
13.1
representation_clause ::=
attribute_definition_clause
| enumeration_representation_clause
| record_representation_clause
| at_clause
13.1
local_name ::=
direct_name
| direct_name'attribute_designator
| library_unit_name
13.3
attribute_definition_clause ::=
for local_name'attribute_designator use expression;
| for local_name'attribute_designator use name;
13.4
enumeration_representation_clause ::=
for first_subtype_local_name use enumeration_aggregate;
13.4
enumeration_aggregate ::= array_aggregate
13.5.1
record_representation_clause ::=
for first_subtype_local_name use
record [mod_clause]
{component_clause}
end record;
13.5.1
component_clause ::=
component_local_name at position range first_bit ┬╖┬╖ last_bit;
13.5.1
position ::= static_expression
13.5.1
first_bit ::= static_simple_expression
13.5.1
last_bit ::= static_simple_expression
13.8
code_statement ::= qualified_expression;
13.12
restriction ::= restriction_identifier
| restriction_parameter_identifier => expression
J.3
delta_constraint ::= delta static_expression [range_constraint]
J.7
at_clause ::= for direct_name use at expression;
J.8
mod_clause ::= at mod static_expression;
SYNTAX CROSS REFERENCE
2.
abort_statement
simple_statement 5.1
abortable_part
asynchronous_select 9.7.4
abstract_subprogram_declaration
basic_declaration 3.1
accept_alternative
select_alternative 9.7.1
accept_statement
accept_alternative 9.7.1
compound_statement 5.1
access_definition
discriminant_specification 3.7
parameter_specification 6.1
access_type_definition
formal_access_type_definition 12.5.4
type_definition 3.2.1
access_to_object_definition
access_type_definition 3.10
access_to_subprogram_definition
access_type_definition 3.10
actual_parameter_part
entry_call_statement 9.5.3
function_call 6.4
procedure_call_statement 6.4
aggregate
primary 4.4
qualified_expression 4.7
allocator
primary 4.4
ancestor_part
extension_aggregate 4.3.2
array_aggregate
aggregate 4.3
enumeration_aggregate 13.4
array_component_association
named_array_aggregate 4.3.3
array_type_definition
formal_array_type_definition 12.5.3
object_declaration 3.3.1
type_definition 3.2.1
assignment_statement
simple_statement 5.1
asynchronous_select
select_statement 9.7
at_clause
representation_clause 13.1
attribute_definition_clause
representation_clause 13.1
attribute_designator
attribute_definition_clause 13.3
attribute_reference 4.1.4
local_name 13.1
attribute_reference
name 4.1
base
based_literal 2.4.2
based_literal
numeric_literal 2.4
based_numeral
based_literal 2.4.2
basic_declaration
basic_declarative_item 3.11
basic_declarative_item
declarative_item 3.11
package_specification 7.1
binary_adding_operator
simple_expression 4.4
block_statement
compound_statement 5.1
body
declarative_item 3.11
body_stub
body 3.11
case_statement
compound_statement 5.1
case_statement_alternative
case_statement 5.4
character
comment 2.7
character_literal
defining_character_literal 3.5.1
name 4.1
selector_name 4.1.3
choice_parameter_specification
exception_handler 11.2
code_statement
simple_statement 5.1
compilation_unit
compilation 10.1.1
component_choice_list
record_component_association 4.3.1
component_clause
record_representation_clause 13.5.1
component_declaration
component_item 3.8
protected_element_declaration 9.4
component_definition
component_declaration 3.8
constrained_array_definition 3.6
unconstrained_array_definition 3.6
component_item
component_list 3.8
component_list
record_definition 3.8
variant 3.8.1
composite_constraint
constraint 3.2.2
compound_statement
statement 5.1
condition
entry_barrier 9.5.2
exit_statement 5.7
guard 9.7.1
if_statement 5.3
iteration_scheme 5.5
conditional_entry_call
select_statement 9.7
constrained_array_definition
array_type_definition 3.6
constraint
subtype_indication 3.2.2
context_clause
compilation_unit 10.1.1
context_item
context_clause 10.1.2
decimal_fixed_point_definition
fixed_point_definition 3.5.9
decimal_literal
numeric_literal 2.4
declarative_item
declarative_part 3.11
declarative_part
block_statement 5.6
entry_body 9.5.2
package_body 7.2
subprogram_body 6.3
task_body 9.1
default_expression
component_declaration 3.8
discriminant_specification 3.7
formal_object_declaration 12.4
parameter_specification 6.1
default_name
subprogram_default 12.6
defining_character_literal
enumeration_literal_specification 3.5.1
defining_designator
generic_instantiation 12.3
subprogram_specification 6.1
defining_identifier
choice_parameter_specification 11.2
defining_identifier_list 3.3.1
defining_program_unit_name 6.1
entry_body 9.5.2
entry_declaration 9.5.2
entry_index_specification 9.5.2
enumeration_literal_specification 3.5.1
exception_renaming_declaration 8.5.2
formal_package_declaration 12.7
formal_type_declaration 12.5
full_type_declaration 3.2.1
incomplete_type_declaration 3.10.1
loop_parameter_specification 5.5
object_renaming_declaration 8.5.1
package_body_stub 10.1.3
private_extension_declaration 7.3
private_type_declaration 7.3
protected_body 9.4
protected_body_stub 10.1.3
protected_type_declaration 9.4
single_protected_declaration 9.4
single_task_declaration 9.1
subtype_declaration 3.2.2
task_body 9.1
task_body_stub 10.1.3
task_type_declaration 9.1
defining_identifier_list
component_declaration 3.8
discriminant_specification 3.7
exception_declaration 11.1
formal_object_declaration 12.4
number_declaration 3.3.2
object_declaration 3.3.1
parameter_specification 6.1
defining_operator_symbol
defining_designator 6.1
defining_program_unit_name
defining_designator 6.1
generic_instantiation 12.3
generic_renaming_declaration 8.5.5
package_body 7.2
package_renaming_declaration 8.5.3
package_specification 7.1
subprogram_specification 6.1
delay_alternative
select_alternative 9.7.1
timed_entry_call 9.7.2
delay_relative_statement
delay_statement 9.6
delay_statement
delay_alternative 9.7.1
simple_statement 5.1
triggering_statement 9.7.4
delay_until_statement
delay_statement 9.6
delta_constraint
scalar_constraint 3.2.2
derived_type_definition
type_definition 3.2.1
designator
subprogram_body 6.3
digit
extended_digit 2.4.2
graphic_character 2.1
letter_or_digit 2.3
numeral 2.4.1
digits_constraint
scalar_constraint 3.2.2
direct_name
accept_statement 9.5.2
at_clause J.7
local_name 13.1
name 4.1
statement_identifier 5.1
variant_part 3.8.1
discrete_choice
discrete_choice_list 3.8.1
discrete_choice_list
array_component_association 4.3.3
case_statement_alternative 5.4
variant 3.8.1
discrete_range
discrete_choice 3.8.1
index_constraint 3.6.1
slice 4.1.2
discrete_subtype_definition
constrained_array_definition 3.6
entry_declaration 9.5.2
entry_index_specification 9.5.2
loop_parameter_specification 5.5
discriminant_association
discriminant_constraint 3.7.1
discriminant_constraint
composite_constraint 3.2.2
discriminant_part
formal_type_declaration 12.5
incomplete_type_declaration 3.10.1
private_extension_declaration 7.3
private_type_declaration 7.3
discriminant_specification
known_discriminant_part 3.7
entry_barrier
entry_body 9.5.2
entry_body
protected_operation_item 9.4
entry_body_formal_part
entry_body 9.5.2
entry_call_alternative
conditional_entry_call 9.7.3
timed_entry_call 9.7.2
entry_call_statement
entry_call_alternative 9.7.2
simple_statement 5.1
triggering_statement 9.7.4
entry_declaration
protected_operation_declaration 9.4
task_item 9.1
entry_index
accept_statement 9.5.2
entry_index_specification
entry_body_formal_part 9.5.2
enumeration_aggregate
enumeration_representation_clause 13.4
enumeration_literal_specification
enumeration_type_definition 3.5.1
enumeration_representation_clause
representation_clause 13.1
enumeration_type_definition
type_definition 3.2.1
exception_choice
exception_handler 11.2
exception_declaration
basic_declaration 3.1
exception_handler
handled_sequence_of_statements 11.2
exception_renaming_declaration
renaming_declaration 8.5
exit_statement
simple_statement 5.1
explicit_actual_parameter
parameter_association 6.4
explicit_dereference
name 4.1
explicit_generic_actual_parameter
generic_association 12.3
exponent
based_literal 2.4.2
decimal_literal 2.4.1
expression
ancestor_part 4.3.2
array_component_association 4.3.3
assignment_statement 5.2
at_clause J.7
attribute_definition_clause 13.3
attribute_designator 4.1.4
case_statement 5.4
condition 5.3
decimal_fixed_point_definition 3.5.9
default_expression 3.7
delay_relative_statement 9.6
delay_until_statement 9.6
delta_constraint J.3
digits_constraint 3.5.9
discrete_choice 3.8.1
discriminant_association 3.7.1
entry_index 9.5.2
explicit_actual_parameter 6.4
explicit_generic_actual_parameter 12.3
floating_point_definition 3.5.7
indexed_component 4.1.1
mod_clause J.8
modular_type_definition 3.5.4
number_declaration 3.3.2
object_declaration 3.3.1
ordinary_fixed_point_definition 3.5.9
position 13.5.1
positional_array_aggregate 4.3.3
pragma_argument_association 2.8
primary 4.4
qualified_expression 4.7
range_attribute_designator 4.1.4
record_component_association 4.3.1
restriction 13.12
return_statement 6.5
type_conversion 4.6
extended_digit
based_numeral 2.4.2
extension_aggregate
aggregate 4.3
factor
term 4.4
first_bit
component_clause 13.5.1
fixed_point_definition
real_type_definition 3.5.6
floating_point_definition
real_type_definition 3.5.6
formal_access_type_definition
formal_type_definition 12.5
formal_array_type_definition
formal_type_definition 12.5
formal_decimal_fixed_point_definition
formal_type_definition 12.5
formal_derived_type_definition
formal_type_definition 12.5
formal_discrete_type_definition
formal_type_definition 12.5
formal_floating_point_definition
formal_type_definition 12.5
formal_modular_type_definition
formal_type_definition 12.5
formal_object_declaration
generic_formal_parameter_declaration 12.1
formal_ordinary_fixed_point_definition
formal_type_definition 12.5
formal_package_actual_part
formal_package_declaration 12.7
formal_package_declaration
generic_formal_parameter_declaration 12.1
formal_part
parameter_and_result_profile 6.1
parameter_profile 6.1
formal_private_type_definition
formal_type_definition 12.5
formal_signed_integer_type_definition
formal_type_definition 12.5
formal_subprogram_declaration
generic_formal_parameter_declaration 12.1
formal_type_declaration
generic_formal_parameter_declaration 12.1
formal_type_definition
formal_type_declaration 12.5
format_effector
character 2.1
full_type_declaration
type_declaration 3.2.1
function_call
name 4.1
general_access_modifier
access_to_object_definition 3.10
generic_actual_part
formal_package_actual_part 12.7
generic_instantiation 12.3
generic_association
generic_actual_part 12.3
generic_declaration
basic_declaration 3.1
library_unit_declaration 10.1.1
generic_formal_parameter_declaration
generic_formal_part 12.1
generic_formal_part
generic_package_declaration 12.1
generic_subprogram_declaration 12.1
generic_instantiation
basic_declaration 3.1
library_unit_declaration 10.1.1
generic_package_declaration
generic_declaration 12.1
generic_renaming_declaration
library_unit_renaming_declaration 10.1.1
renaming_declaration 8.5
generic_subprogram_declaration
generic_declaration 12.1
goto_statement
simple_statement 5.1
graphic_character
character 2.1
character_literal 2.5
string_element 2.6
guard
selective_accept 9.7.1
handled_sequence_of_statements
accept_statement 9.5.2
block_statement 5.6
entry_body 9.5.2
package_body 7.2
subprogram_body 6.3
task_body 9.1
identifier
accept_statement 9.5.2
attribute_designator 4.1.4
block_statement 5.6
defining_identifier 3.1
designator 6.1
direct_name 4.1
entry_body 9.5.2
loop_statement 5.5
package_body 7.2
package_specification 7.1
pragma 2.8
pragma_argument_association 2.8
protected_body 9.4
protected_definition 9.4
restriction 13.12
selector_name 4.1.3
task_body 9.1
task_definition 9.1
identifier_letter
graphic_character 2.1
identifier 2.3
letter_or_digit 2.3
if_statement
compound_statement 5.1
implicit_dereference
prefix 4.1
incomplete_type_declaration
type_declaration 3.2.1
index_constraint
composite_constraint 3.2.2
index_subtype_definition
unconstrained_array_definition 3.6
indexed_component
name 4.1
integer_type_definition
type_definition 3.2.1
iteration_scheme
loop_statement 5.5
known_discriminant_part
discriminant_part 3.7
full_type_declaration 3.2.1
protected_type_declaration 9.4
task_type_declaration 9.1
label
statement 5.1
last_bit
component_clause 13.5.1
letter_or_digit
identifier 2.3
library_item
compilation_unit 10.1.1
library_unit_body
library_item 10.1.1
library_unit_declaration
library_item 10.1.1
library_unit_renaming_declaration
library_item 10.1.1
local_name
attribute_definition_clause 13.3
component_clause 13.5.1
enumeration_representation_clause 13.4
record_representation_clause 13.5.1
loop_parameter_specification
iteration_scheme 5.5
loop_statement
compound_statement 5.1
mod_clause
record_representation_clause 13.5.1
mode
formal_object_declaration 12.4
parameter_specification 6.1
modular_type_definition
integer_type_definition 3.5.4
multiplying_operator
term 4.4
name
abort_statement 9.8
assignment_statement 5.2
attribute_definition_clause 13.3
default_name 12.6
entry_call_statement 9.5.3
exception_choice 11.2
exception_renaming_declaration 8.5.2
exit_statement 5.7
explicit_actual_parameter 6.4
explicit_dereference 4.1
explicit_generic_actual_parameter 12.3
formal_package_declaration 12.7
function_call 6.4
generic_instantiation 12.3
generic_renaming_declaration 8.5.5
goto_statement 5.8
implicit_dereference 4.1
local_name 13.1
object_renaming_declaration 8.5.1
package_renaming_declaration 8.5.3
parent_unit_name 10.1.1
pragma_argument_association 2.8
prefix 4.1
primary 4.4
procedure_call_statement 6.4
raise_statement 11.3
requeue_statement 9.5.4
subprogram_renaming_declaration 8.5.4
subtype_mark 3.2.2
type_conversion 4.6
use_package_clause 8.4
with_clause 10.1.2
named_array_aggregate
array_aggregate 4.3.3
null_statement
simple_statement 5.1
number_declaration
basic_declaration 3.1
numeral
base 2.4.2
decimal_literal 2.4.1
exponent 2.4.1
numeric_literal
primary 4.4
object_declaration
basic_declaration 3.1
object_renaming_declaration
renaming_declaration 8.5
operator_symbol
defining_operator_symbol 6.1
designator 6.1
direct_name 4.1
selector_name 4.1.3
ordinary_fixed_point_definition
fixed_point_definition 3.5.9
other_control_function
character 2.1
package_body
library_unit_body 10.1.1
proper_body 3.11
package_body_stub
body_stub 10.1.3
package_declaration
basic_declaration 3.1
library_unit_declaration 10.1.1
package_renaming_declaration
library_unit_renaming_declaration 10.1.1
renaming_declaration 8.5
package_specification
generic_package_declaration 12.1
package_declaration 7.1
parameter_and_result_profile
access_to_subprogram_definition 3.10
subprogram_specification 6.1
parameter_association
actual_parameter_part 6.4
parameter_profile
accept_statement 9.5.2
access_to_subprogram_definition 3.10
entry_body_formal_part 9.5.2
entry_declaration 9.5.2
subprogram_specification 6.1
parameter_specification
formal_part 6.1
parent_unit_name
defining_program_unit_name 6.1
designator 6.1
package_body 7.2
package_specification 7.1
subunit 10.1.3
position
component_clause 13.5.1
positional_array_aggregate
array_aggregate 4.3.3
pragma_argument_association
pragma 2.8
prefix
attribute_reference 4.1.4
function_call 6.4
indexed_component 4.1.1
procedure_call_statement 6.4
range_attribute_reference 4.1.4
selected_component 4.1.3
slice 4.1.2
primary
factor 4.4
private_extension_declaration
type_declaration 3.2.1
private_type_declaration
type_declaration 3.2.1
procedure_call_statement
simple_statement 5.1
proper_body
body 3.11
subunit 10.1.3
protected_body
proper_body 3.11
protected_body_stub
body_stub 10.1.3
protected_definition
protected_type_declaration 9.4
single_protected_declaration 9.4
protected_element_declaration
protected_definition 9.4
protected_operation_declaration
protected_definition 9.4
protected_element_declaration 9.4
protected_operation_item
protected_body 9.4
protected_type_declaration
full_type_declaration 3.2.1
qualified_expression
allocator 4.8
code_statement 13.8
primary 4.4
raise_statement
simple_statement 5.1
range
discrete_range 3.6.1
discrete_subtype_definition 3.6
range_constraint 3.5
relation 4.4
range_attribute_designator
range_attribute_reference 4.1.4
range_attribute_reference
range 3.5
range_constraint
delta_constraint J.3
digits_constraint 3.5.9
scalar_constraint 3.2.2
real_range_specification
decimal_fixed_point_definition 3.5.9
floating_point_definition 3.5.7
ordinary_fixed_point_definition 3.5.9
real_type_definition
type_definition 3.2.1
record_aggregate
aggregate 4.3
record_component_association
record_component_association_list 4.3.1
record_component_association_list
extension_aggregate 4.3.2
record_aggregate 4.3.1
record_definition
record_extension_part 3.9.1
record_type_definition 3.8
record_extension_part
derived_type_definition 3.4
record_representation_clause
representation_clause 13.1
record_type_definition
type_definition 3.2.1
relation
expression 4.4
relational_operator
relation 4.4
renaming_declaration
basic_declaration 3.1
representation_clause
basic_declarative_item 3.11
component_item 3.8
protected_operation_declaration 9.4
protected_operation_item 9.4
task_item 9.1
requeue_statement
simple_statement 5.1
return_statement
simple_statement 5.1
scalar_constraint
constraint 3.2.2
select_alternative
selective_accept 9.7.1
select_statement
compound_statement 5.1
selected_component
name 4.1
selective_accept
select_statement 9.7
selector_name
component_choice_list 4.3.1
discriminant_association 3.7.1
generic_association 12.3
parameter_association 6.4
selected_component 4.1.3
sequence_of_statements
abortable_part 9.7.4
accept_alternative 9.7.1
case_statement_alternative 5.4
conditional_entry_call 9.7.3
delay_alternative 9.7.1
entry_call_alternative 9.7.2
exception_handler 11.2
handled_sequence_of_statements 11.2
if_statement 5.3
loop_statement 5.5
selective_accept 9.7.1
triggering_alternative 9.7.4
signed_integer_type_definition
integer_type_definition 3.5.4
simple_expression
first_bit 13.5.1
last_bit 13.5.1
range 3.5
real_range_specification 3.5.7
relation 4.4
signed_integer_type_definition 3.5.4
simple_statement
statement 5.1
single_protected_declaration
object_declaration 3.3.1
single_task_declaration
object_declaration 3.3.1
slice
name 4.1
space_character
graphic_character 2.1
special_character
graphic_character 2.1
statement
sequence_of_statements 5.1
statement_identifier
block_statement 5.6
label 5.1
loop_statement 5.5
string_element
string_literal 2.6
string_literal
operator_symbol 6.1
primary 4.4
subprogram_body
library_unit_body 10.1.1
proper_body 3.11
protected_operation_item 9.4
subprogram_body_stub
body_stub 10.1.3
subprogram_declaration
basic_declaration 3.1
library_unit_declaration 10.1.1
protected_operation_declaration 9.4
protected_operation_item 9.4
subprogram_default
formal_subprogram_declaration 12.6
subprogram_renaming_declaration
library_unit_renaming_declaration 10.1.1
renaming_declaration 8.5
subprogram_specification
abstract_subprogram_declaration 6.1
formal_subprogram_declaration 12.6
generic_subprogram_declaration 12.1
subprogram_body 6.3
subprogram_body_stub 10.1.3
subprogram_declaration 6.1
subprogram_renaming_declaration 8.5.4
subtype_declaration
basic_declaration 3.1
subtype_indication
access_to_object_definition 3.10
allocator 4.8
component_definition 3.6
derived_type_definition 3.4
discrete_range 3.6.1
discrete_subtype_definition 3.6
object_declaration 3.3.1
private_extension_declaration 7.3
subtype_declaration 3.2.2
subtype_mark
access_definition 3.10
ancestor_part 4.3.2
discriminant_specification 3.7
explicit_generic_actual_parameter 12.3
formal_derived_type_definition 12.5.1
formal_object_declaration 12.4
index_subtype_definition 3.6
object_renaming_declaration 8.5.1
parameter_and_result_profile 6.1
parameter_specification 6.1
qualified_expression 4.7
relation 4.4
subtype_indication 3.2.2
type_conversion 4.6
use_type_clause 8.4
subunit
compilation_unit 10.1.1
task_body
proper_body 3.11
task_body_stub
body_stub 10.1.3
task_definition
single_task_declaration 9.1
task_type_declaration 9.1
task_item
task_definition 9.1
task_type_declaration
full_type_declaration 3.2.1
term
simple_expression 4.4
terminate_alternative
select_alternative 9.7.1
timed_entry_call
select_statement 9.7
triggering_alternative
asynchronous_select 9.7.4
triggering_statement
triggering_alternative 9.7.4
type_conversion
name 4.1
type_declaration
basic_declaration 3.1
type_definition
full_type_declaration 3.2.1
unary_adding_operator
simple_expression 4.4
unconstrained_array_definition
array_type_definition 3.6
underline
based_numeral 2.4.2
identifier 2.3
numeral 2.4.1
unknown_discriminant_part
discriminant_part 3.7
use_clause
basic_declarative_item 3.11
context_item 10.1.2
generic_formal_part 12.1
use_package_clause
use_clause 8.4
use_type_clause
use_clause 8.4
variant
variant_part 3.8.1
variant_part
component_list 3.8
with_clause
context_item 10.1.2
ΓòÉΓòÉΓòÉ 30.1. Index ΓòÉΓòÉΓòÉ
Index entries are given by paragraph number. A list of all
language-defined library units may be found under Language-Defined
Library Units. A list of all language-defined types may be found under
Language-Defined Types.
Index.Operators Index.Operators
Index.Digits Index.Digits
Index.A Index.A
Index.B Index.B
Index.C Index.C
Index.D Index.D
Index.E Index.E
Index.F Index.F
Index.G Index.G
Index.H Index.H
Index.I Index.I
Index.J Index.J
Index.K Index.K
Index.L Index.L
Index.M Index.M
Index.N Index.N
Index.O Index.O
Index.P Index.P
Index.Q Index.Q
Index.R Index.R
Index.S Index.S
Index.T Index.T
Index.U Index.U
Index.V Index.V
Index.W Index.W
Index.X Index.X
Index.Y Index.Y
ΓòÉΓòÉΓòÉ 30.2. Operator index ΓòÉΓòÉΓòÉ
& operator 4.4(1), 4.5.3(1), 4.5.3(3)
* operator 4.4(1), 4.5.5(1), 4.5.5(1)
** operator 4.4(1), 4.5.6(1), 4.5.6(7)
+ operator 4.4(1), 4.5.3(1), 4.5.4(1), see 4.5.3(1), see 4.5.4(1)
= operator 4.4(1), 4.5.2(1), 4.5.2(1)
- operator 4.4(1), 4.5.3(1), 4.5.4(1), see 4.5.3(1), see 4.5.4(1)
/ operator 4.4(1), 4.5.5(1), 4.5.5(1)
/= operator 4.4(1), 4.5.2(1), 4.5.2(1)
< operator 4.4(1), 4.5.2(1), 4.5.2(1)
<= operator 4.4(1), 4.5.2(1), 4.5.2(1)
> operator 4.4(1), 4.5.2(1), 4.5.2(1)
>= operator 4.4(1), 4.5.2(1), 4.5.2(1)
ΓòÉΓòÉΓòÉ 30.3. Digits index ΓòÉΓòÉΓòÉ
10646-1:1993, ISO/IEC standard 1.2(8).
1539:1991, ISO/IEC standard 1.2(3).
1989:1985, ISO standard 1.2(4).
6429:1992, ISO/IEC standard 1.2(5).
646:1991, ISO/IEC standard 1.2(2).
8859-1:1987, ISO/IEC standard 1.2(6).
9899:1990, ISO/IEC standard 1.2(7).
ΓòÉΓòÉΓòÉ 31. index ΓòÉΓòÉΓòÉ
A_Form 4.6.
abnormal completion 7.6.1.
abnormal state of an object 13.9.1.
[partial] 9.8(21), see 11.6(6), see A.13(21), see 11.6(6), see A.13(17).
abnormal task 9.8.
abort
of a partition E.1.
of a task 9.8.
of the execution of a construct 9.8.
abort completion point 9.8.
abort-deferred operation 9.8.
abort_statement 9.8.
used 5.1(4), see P(4), see P(1).
Abort_Task C.7.1.
abortable_part 9.7.4.
used 9.7.4(2), see P(2), see P(1).
abs operator 4.4(1), see 4.5.6(1), see 4.5.6(1).
absolute value 4.4(1), see 4.5.6(1), see 4.5.6(1).
abstract data type (ADT)
See also abstract type 3.9.3.
See private types and private extensions 7.3.
abstract subprogram 3.9.3(1), see 3.9.3(1), see 3.9.3(3).
abstract type 3.9.3(1), see 3.9.3(1), see 3.9.3(2).
abstract_subprogram_declaration 6.1.
used 3.1(3), see P(3), see P(1).
Acc 13.11.
accept_alternative 9.7.1.
used 9.7.1(4), see P(4), see P(1).
accept_statement 9.5.2.
used 5.1(5), see 9.7.1(5), see P(5), see 9.7.1(5), see P(1).
acceptable interpretation 8.6.
Access attribute 3.10.2(24), see 3.10.2(24), see 3.10.2(32),
K(2), K(2), K(4).
See also Unchecked_Access attribute 13.10.
access discriminant 3.7.
access parameter 6.1.
access paths
distinct 6.2.
access type 3.10(1), see N(1), see N(2).
access types
input-output unspecified A.7.
access value 3.10.
access-to-constant type 3.10.
access-to-object type 3.10.
access-to-subprogram type 3.10(7), see 3.10(7), see 3.10(11).
access-to-variable type 3.10.
Access_Check 11.5.
[partial] 4.1(13), see 4.6(13), see 4.6(49).
access_definition 3.10.
used 3.7(5), see 6.1(15), see P(5), see 6.1(15), see P(1).
access_type_definition 3.10.
used 3.2.1(4), see 12.5.4(2), see P(4), see 12.5.4(2), see P(1).
access_to_object_definition 3.10.
used 3.10(2), see P(2), see P(1).
access_to_subprogram_definition 3.10.
used 3.10(2), see P(2), see P(1).
accessibility
from shared passive library units E.2.1.
accessibility level 3.10.2.
accessibility rule
Access attribute 3.10.2(28), see 3.10.2(28), see 3.10.2(32).
record extension 3.9.1.
requeue statement 9.5.4.
type conversion 4.6(17), see 4.6(17), see 4.6(20).
Accessibility_Check 11.5.
[partial] 3.10.2(29), see 4.6(48), see 6.5(29), see 4.6(48), see 6.5(17),
E.4.
accessible partition E.1.
accuracy 4.6(32), see G.2(32), see G.2(1).
ACK A.3.3(5), see J.5(5), see J.5(4).
acquire
execution resource associated with protected object
9.5.1.
Activate 6.4.
activation
of a task 9.2.
activation failure 9.2.
activator
of a task 9.2.
active partition 10.2(28), see E.1(28), see E.1(2).
active priority D.1.
actual 12.3.
actual duration D.9.
actual parameter
for a formal parameter 6.4.1.
actual subtype 3.3(23), see 12.5(23), see 12.5(4).
of an object 3.3.1.
actual type 12.5.
actual_parameter_part 6.4.
used 6.4(2), see 6.4(3), see 9.5.3(2), see P(2), see 6.4(3), see 9.5.3(2), see P(1).
Acute A.3.3.
Ada A.2.
Ada calling convention 6.3.1.
Ada.Asynchronous_Task_Control D.11.
Ada.Calendar 9.6.
Ada.Characters A.3.1.
Ada.Characters.Handling A.3.2.
Ada.Characters.Latin_1 A.3.3.
Ada.Command_Line A.15.
Ada.Decimal F.2.
Ada.Direct_IO A.8.4.
Ada.Dynamic_Priorities D.5.
Ada.Exceptions 11.4.1.
Ada.Finalization 7.6.
Ada.Float_Text_IO A.10.9.
Ada.Float_Wide_Text_IO A.11.
Ada.Integer_Text_IO A.10.8.
Ada.Integer_Wide_Text_IO A.11.
Ada.Interrupts C.3.2.
Ada.Interrupts.Names C.3.2.
Ada.Numerics A.5.
Ada.Numerics.Complex_Elementary_Functions G.1.2.
Ada.Numerics.Complex_Types G.1.1.
Ada.Numerics.Discrete_Random A.5.2.
Ada.Numerics.Elementary_Functions A.5.1.
Ada.Numerics.Float_Random A.5.2.
Ada.Numerics.Generic_Complex_Elementary_Functions G.1.2.
Ada.Numerics.Generic_Complex_Types G.1.1.
Ada.Numerics.Generic_Elementary_Functions A.5.1.
Ada.Real_Time D.8.
Ada.Sequential_IO A.8.1.
Ada.Storage_IO A.9.
Ada.Streams 13.13.1.
Ada.Streams.Stream_IO A.12.1.
Ada.Strings A.4.1.
Ada.Strings.Bounded A.4.4.
Ada.Strings.Fixed A.4.3.
Ada.Strings.Maps A.4.2.
Ada.Strings.Maps.Constants A.4.6.
Ada.Strings.Unbounded A.4.5.
Ada.Strings.Wide_Bounded A.4.7.
Ada.Strings.Wide_Fixed A.4.7.
Ada.Strings.Wide_Maps A.4.7.
Ada.Strings.Wide_Maps.Wide_Constants A.4.7.
Ada.Strings.Wide_Unbounded A.4.7.
Ada.Synchronous_Task_Control D.10.
Ada.Tags 3.9.
Ada.Task_Attributes C.7.2.
Ada.Task_Identification C.7.1.
Ada.Text_IO A.10.1.
Ada.Text_IO.Complex_IO G.1.3.
Ada.Text_IO.Editing F.3.3.
Ada.Text_IO.Text_Streams A.12.2.
Ada.Unchecked_Conversion 13.9.
Ada.Unchecked_Deallocation 13.11.2.
Ada.Wide_Text_IO A.11.
Ada.Wide_Text_IO.Complex_IO G.1.4.
Ada.Wide_Text_IO.Editing F.3.4.
Ada.Wide_Text_IO.Text_Streams A.12.3.
Ada.IO_Exceptions A.13.
Ada_Application B.5.
Ada_Employee_Record_Type B.4.
Addition 3.9.1.
Address 13.7.
arithmetic 13.7.1.
comparison 13.7.
null 13.7.
Address attribute 13.3(11), see J.7.1(5), see K(11), see J.7.1(5), see K(6).
Address clause 13.3(7), see 13.3(7), see 13.3(12).
Address_To_Access_Conversions
child of System 13.7.2.
Adjacent attribute A.5.3(48), see K(48), see K(8).
Adjust 7.6(2), see 7.6(2), see 7.6(6).
adjusting the value of an object 7.6(15), see 7.6(15), see 7.6(16).
adjustment 7.6(15), see 7.6(15), see 7.6(16).
as part of assignment 5.2.
Adjustments_Conversions B.4.
Adjustments_Type B.4.
ADT (abstract data type)
See also abstract type 3.9.3.
See private types and private extensions 7.3.
advice 1.1.2.
Aft attribute 3.5.10(5), see K(5), see K(12).
aggregate 4.3(1), see 4.3(1), see 4.3(2).
used 4.4(7), see 4.7(2), see P(7), see 4.7(2), see P(1).
See also composite type 3.2.
aliased 3.10(9), see N(9), see N(3).
aliasing
See distinct access paths 6.2.
Alignment A.4.1.
Alignment attribute 13.3(23), see K(23), see K(14).
Alignment clause 13.3(7), see 13.3(7), see 13.3(25).
All_Calls_Remote pragma E.2.3(5), see L(5), see L(2).
All_Checks 11.5.
Allocate 13.11.
allocator 4.8.
used 4.4(7), see P(7), see P(1).
Alphanumeric B.4.
alphanumeric character
a category of Character A.3.2.
Alphanumeric_Set A.4.6.
ambiguous 8.6.
ampersand 2.1(15), see A.3.3(8)
ampersand operator 4.4(1), see 4.5.3(1), see 4.5.3(3).
ancestor
of a library unit 10.1.1.
of a type 3.4.1.
ultimate 3.4.1.
ancestor subtype
of a private_extension_declaration 7.3.
of a formal derived type 12.5.1.
ancestor_part 4.3.2.
used 4.3.2(2), see P(2), see P(1).
and operator 4.4(1), see 4.5.1(1), see 4.5.1(2).
and then (short-circuit control form) 4.4,
4.5.1.
Angle 12.5.
angle threshold G.2.4.
Annex
informative 1.1.2.
normative 1.1.2.
Specialized Needs 1.1.2.
anonymous access type 3.10.
anonymous array type 3.3.1.
anonymous protected type 3.3.1.
anonymous task type 3.3.1.
anonymous type 3.2.1.
Any_Priority 13.7(16), see D.1(16), see D.1(10).
APC A.3.3.
apostrophe 2.1(15), see A.3.3(15), see A.3.3(8).
Append A.4.4(13), see A.4.4(14), see A.4.4(13), see A.4.4(14), see A.4.4(15),
A.4.4(16), see A.4.4(17), see A.4.4(16), see A.4.4(17), see A.4.4(18),
A.4.4(19), see A.4.4(20), see A.4.5(19), see A.4.4(20), see A.4.5(12),
A.4.5(13), see A.4.5(13), see A.4.5(14).
applicable index constraint 4.3.3.
application areas 1.1.2.
apply
to a loop_statement by an exit_statement 5.7.
to a callable construct by a return_statement 6.5.
to a program unit by a program unit pragma 10.1.5.
arbitrary order 1.1.4.
Arccos A.5.1(6), see G.1.2(6), see G.1.2(5).
Arccosh A.5.1(7), see G.1.2(7), see G.1.2(7).
Arccot A.5.1(6), see G.1.2(6), see G.1.2(5).
Arccoth A.5.1(7), see G.1.2(7), see G.1.2(7).
Arcsin A.5.1(6), see G.1.2(5)
Arcsinh A.5.1(7), see G.1.2(7), see G.1.2(7).
Arctan A.5.1(6), see G.1.2(6), see G.1.2(5).
Arctanh A.5.1(7), see G.1.2(7), see G.1.2(7).
Argument A.15(5), see G.1.1(5), see G.1.1(10).
argument of a pragma 2.8.
Argument_Count A.15.
Argument_Error A.5.
array 3.6.
array component expression 4.3.3.
array indexing
See indexed_component 4.1.1.
array slice 4.1.2.
array type 3.6(1), see N(1), see N(4).
array_aggregate 4.3.3.
used 4.3(2), see 13.4(3), see P(2), see 13.4(3), see P(1).
array_component_association 4.3.3.
used 4.3.3(4), see P(4), see P(1).
array_type_definition 3.6.
used 3.2.1(4), see 3.3.1(2), see 12.5.3(4), see 3.3.1(2), see 12.5.3(2),
P.
ASCII A.1(36), see J.5(36), see J.5(2).
package physically nested within the declaration of Standard
A.1.
aspect of representation 13.1.
coding 13.4.
controlled 13.11.3.
convention, calling convention B.1.
exported B.1.
imported B.1.
layout 13.5.
packing 13.2.
record layout 13.5.
specifiable attributes 13.3.
storage place 13.5.
assembly language C.1.
assign
See assignment operation 5.2.
assigning back of parameters 6.4.1.
assignment
user-defined 7.6.
assignment operation 5.2(3), see 5.2(12), see 7.6(3), see 5.2(12), see 7.6(13).
during elaboration of an object_declaration 3.3.1.
during evaluation of a generic_association for a formal object
of mode in 12.4(11)
during evaluation of a parameter_association 6.4.1.
during evaluation of an aggregate 4.3.
during evaluation of an initialized allocator 4.8.
during evaluation of an uninitialized allocator 4.8,
4.8.
during evaluation of concatenation 4.5.3.
during execution of a for loop 5.5.
during execution of a return_statement 6.5.
during execution of an assignment_statement 5.2.
during parameter copy back 6.4.1.
assignment_statement 5.2.
used 5.1(4), see P(4), see P(1).
associated components
of a record_component_association 4.3.1.
associated discriminants
of a named discriminant_association 3.7.1.
of a positional discriminant_association 3.7.1.
associated object
of a value of a by-reference type 6.2.
asterisk 2.1(15), see A.3.3(15), see A.3.3(8).
asynchronous
remote procedure call E.4.1.
Asynchronous pragma E.4.1(3), see L(3), see L(3).
asynchronous remote procedure call E.4.
asynchronous_select 9.7.4.
used 9.7(2), see P(2), see P(1).
Asynchronous_Task_Control
child of Ada D.11.
at-most-once execution E.4.
at_clause J.7.
used 13.1(2), see P(2), see P(1).
atomic C.6.
Atomic pragma C.6(3), see L(3), see L(4).
Atomic_Components pragma C.6(5), see L(5), see L(5).
Attach_Handler C.3.2.
Attach_Handler pragma C.3.1, L(6)
attaching
to an interrupt C.3.
attribute 4.1.4(1), see C.7.2(2), see K(1), see C.7.2(2), see K(1).
representation 13.3.
specifiable 13.3.
specifying 13.3.
attribute_definition_clause 13.3.
used 13.1(2), see P(2), see P(1).
attribute_designator 4.1.4.
used 4.1.4(2), see 13.1(3), see 13.3(2), see 13.1(3), see 13.3(2),
P.
Attribute_Handle C.7.2.
attribute_reference 4.1.4.
used 4.1(2), see P(2), see P(1).
attributes
Access 3.10.2(24), see 3.10.2(32), see K(24), see 3.10.2(32), see K(2),
K.
Address 13.3(11), see J.7.1(5), see K(11), see J.7.1(5), see K(6).
Adjacent A.5.3(48), see K(48), see K(8).
Aft 3.5.10(5), see K(5), see K(12).
Alignment 13.3(23), see K(23), see K(14).
Base 3.5(15), see K(15), see K(17).
Bit_Order 13.5.3(4), see K(4), see K(19).
Body_Version E.3(4), see K(4), see K(21).
Callable 9.9(2), see K(2), see K(23).
Caller C.7.1(14), see K(14), see K(25).
Ceiling A.5.3(33), see K(33), see K(27).
Class 3.9(14), see 7.3.1(9), see K(14), see 7.3.1(9), see K(31),
K.
Component_Size 13.3(69), see K(69), see K(36).
Compose A.5.3(24), see K(24), see K(38).
Constrained 3.7.2(3), see J.4(2), see K(3), see J.4(2), see K(42).
Copy_Sign A.5.3(51), see K(51), see K(44).
Count 9.9(5), see K(5), see K(48).
Definite 12.5.1(23), see K(23), see K(50).
Delta 3.5.10(3), see K(3), see K(52).
Denorm A.5.3(9), see K(9), see K(54).
Digits 3.5.8(2), see 3.5.10(7), see K(2), see 3.5.10(7), see K(56),
K.
Exponent A.5.3(18), see K(18), see K(60).
External_Tag 13.3(75), see K(75), see K(64).
First 3.5(12), see 3.6.2(3), see K(12), see 3.6.2(3), see K(68),
K.
First(N) 3.6.2(4), see K(4), see K(66).
First_Bit 13.5.2(3), see K(3), see K(72).
Floor A.5.3(30), see K(30), see K(74).
Fore 3.5.10(4), see K(4), see K(78).
Fraction A.5.3(21), see K(21), see K(80).
Identity 11.4.1(9), see C.7.1(12), see K(9), see C.7.1(12), see K(84),
K.
Image 3.5(35), see K(35), see K(88).
Input 13.13.2(22), see 13.13.2(32), see K(22), see 13.13.2(32), see K(92),
K.
Last 3.5(13), see 3.6.2(5), see K(13), see 3.6.2(5), see K(102),
K.
Last(N) 3.6.2(6), see K(6), see K(100).
Last_Bit 13.5.2(4), see K(4), see K(106).
Leading_Part A.5.3(54), see K(54), see K(108).
Length 3.6.2(9), see K(9), see K(117).
Length(N) 3.6.2(10), see K(10), see K(115).
Machine A.5.3(60), see K(60), see K(119).
Machine_Emax A.5.3(8), see K(8), see K(123).
Machine_Emin A.5.3(7), see K(125)
Machine_Mantissa A.5.3(6), see K(6), see K(127).
Machine_Overflows A.5.3(12), see A.5.4(12), see A.5.4(4),
K(129), K(129), K(131).
Machine_Radix A.5.3(2), see A.5.4(2), see K(2), see A.5.4(2), see K(133),
K.
Machine_Rounds A.5.3(11), see A.5.4(11), see A.5.4(3),
K(137), K(137), K(139).
Max 3.5(19), see K(19), see K(141).
Max_Size_In_Storage_Elements 13.11.1(3), see K(3), see K(145).
Min 3.5(16), see K(147)
Model A.5.3(68), see G.2.2(7), see K(68), see G.2.2(7), see K(151).
Model_Emin A.5.3(65), see G.2.2(4), see K(155)
Model_Epsilon A.5.3(66), see K(66), see K(157).
Model_Mantissa A.5.3(64), see G.2.2(3), see K(64), see G.2.2(3), see K(159).
Model_Small A.5.3(67), see K(67), see K(161).
Modulus 3.5.4(17), see K(17), see K(163).
Output 13.13.2(19), see 13.13.2(29), see K(19), see 13.13.2(29), see K(165),
K.
Partition_ID E.1(9), see K(9), see K(173).
Pos 3.5.5(2), see K(2), see K(175).
Position 13.5.2(2), see K(2), see K(179).
Pred 3.5(25), see K(25), see K(181).
Range 3.5(14), see 3.6.2(7), see K(14), see 3.6.2(7), see K(187),
K.
Range(N) 3.6.2(8), see K(8), see K(185).
Read 13.13.2(6), see 13.13.2(14), see K(6), see 13.13.2(14), see K(191),
K.
Remainder A.5.3(45), see K(45), see K(199).
Round 3.5.10(12), see K(12), see K(203).
Rounding A.5.3(36), see K(36), see K(207).
Safe_First A.5.3(71), see G.2.2(5), see K(71), see G.2.2(5), see K(211).
Safe_Last A.5.3(72), see G.2.2(6), see K(72), see G.2.2(6), see K(213).
Scale 3.5.10(11), see K(11), see K(215).
Scaling A.5.3(27), see K(27), see K(217).
Signed_Zeros A.5.3(13), see K(13), see K(221).
Size 13.3(40), see 13.3(45), see K(40), see 13.3(45), see K(223),
K.
Small 3.5.10(2), see K(2), see K(230).
Storage_Pool 13.11(13), see K(13), see K(232).
Storage_Size 13.3(60), see 13.11(14), see J.9(60), see 13.11(14), see J.9(2),
K(234), see K(234), see K(236).
Succ 3.5(22), see K(22), see K(238).
Tag 3.9(16), see 3.9(18), see K(16), see 3.9(18), see K(242),
K.
Terminated 9.9(3), see K(3), see K(246).
Truncation A.5.3(42), see K(42), see K(248).
Unbiased_Rounding A.5.3(39), see K(39), see K(252).
Unchecked_Access 13.10(3), see H.4(18), see K(3), see H.4(18), see K(256).
Val 3.5.5(5), see K(5), see K(258).
Valid 13.9.2(3), see H(6), see K(3), see H(6), see K(262).
Value 3.5(52), see K(52), see K(264).
Version E.3(3), see K(3), see K(268).
Wide_Image 3.5(28), see K(28), see K(270).
Wide_Value 3.5(40), see K(40), see K(274).
Wide_Width 3.5(38), see K(38), see K(278).
Width 3.5(39), see K(39), see K(280).
Write 13.13.2(3), see 13.13.2(11), see K(3), see 13.13.2(11), see K(282),
K.
ΓòÉΓòÉΓòÉ 32. index ΓòÉΓòÉΓòÉ
Backus-Naur Form (BNF)
complete listing P.
cross reference P.
notation 1.1.4.
under Syntax heading 1.1.2.
base 2.4.2(3), see 2.4.2(3), see 2.4.2(6).
base 16 literal 2.4.2.
used 2.4.2(2), see P(2), see P(1).
base 2 literal 2.4.2.
base 8 literal 2.4.2.
Base attribute 3.5(15), see K(15), see K(17).
base decimal precision
of a floating point type 3.5.7(9), see 3.5.7(9), see 3.5.7(10).
base priority D.1.
base range
of a decimal fixed point type 3.5.9.
of a fixed point type 3.5.9.
of a floating point type 3.5.7(8), see 3.5.7(8), see 3.5.7(10).
of a modular type 3.5.4.
of a scalar type 3.5.
of a signed integer type 3.5.4.
of an ordinary fixed point type 3.5.9.
base subtype
of a type 3.5.
based_literal 2.4.2.
used 2.4(2), see P(2), see P(1).
based_numeral 2.4.2.
used 2.4.2(2), see P(2), see P(1).
basic letter
a category of Character A.3.2.
basic_declaration 3.1.
used 3.11(4), see P(4), see P(1).
basic_declarative_item 3.11.
used 3.11(3), see 7.1(3), see P(3), see 7.1(3), see P(1).
Basic_Map A.4.6.
Basic_Set A.4.6.
become nonlimited 7.3.1(5), see 7.5(5), see 7.5(16).
BEL A.3.3.
belong
to a range 3.5.
to a subtype 3.2.
Bias 12.2.
bibliography 1.2.
big endian 13.5.3.
binary B.4.
literal 2.4.2.
binary adding operator 4.5.3.
binary literal 2.4.2.
binary operator 4.5.
binary_adding_operator 4.5.
used 4.4(4), see P(4), see P(1).
Binary_Format B.4.
Binary_Operation 3.9.1.
Binop_Ptr 3.10.
bit field
See record_representation_clause 13.5.1.
bit ordering 13.5.3.
bit string
See logical operators on boolean arrays 4.5.1.
Bit_Order 13.7.
Bit_Order attribute 13.5.3(4), see K(4), see K(19).
Bit_Order clause 13.3(7), see 13.5.3(7), see 13.5.3(4).
Bit_Vector 3.6.
blank
in text input for enumeration and numeric types A.10.6.
block_statement 5.6.
used 5.1(5), see P(5), see P(1).
blocked
[partial] D.2.1.
a task state 9.
during an entry call 9.5.3.
execution of a selective_accept 9.7.1.
on a delay_statement 9.6.
on an accept_statement 9.5.2.
waiting for activations to complete 9.2.
waiting for dependents to terminate 9.3.
blocked interrupt C.3.
blocking, potentially .see 9.5.1(8)
Abort_Task C.7.1.
delay_statement 9.6(34), see D.9(34), see D.9(5).
remote subprogram call E.4.
RPC operations E.5.
Suspend_Until_True D.10.
BMP 3.5.2(2), see 3.5.2(2), see 3.5.2(3).
BNF (Backus-Naur Form)
complete listing P.
cross reference P.
notation 1.1.4.
under Syntax heading 1.1.2.
body 3.11.
used 3.11(3), see P(3), see P(1).
body_stub 10.1.3.
used 3.11(5), see P(5), see P(1).
Body_Version attribute E.3(4), see K(4), see K(21).
Boolean 3.5.3(1), see A.1(1), see A.1(5).
boolean type 3.5.3.
Bounded
child of Ada.Strings A.4.4.
bounded error 1.1.2(31), 1.1.5(8), 6.2(31), 1.1.5(8), 6.2(12),
7.6.1(14), 9.5.1(8), 9.8(14), 9.5.1(8), 9.8(20),
10.2(26), 13.9.1(26), 13.9.1(9),
13.11.2(11), see C.7.1(17), see D.5(11), see C.7.1(17), see D.5(11),
E.1(10), E.3(6), J.7.1(10), E.3(6), J.7.1(11).
Bounded_String A.4.4.
bounds
of a discrete_range 3.6.1.
of an array 3.6.
of the index range of an array_aggregate 4.3.3.
box
compound delimiter 3.6.
broadcast signal
See protected object 9.4.
See requeue 9.5.4.
Broken_Bar A.3.3.
BS A.3.3(5), see J.5(5), see J.5(4).
Buffer 3.7(33), see 9.11(8), see 9.11(33), see 9.11(8), see 9.11(9),
12.5.
Buffer_Size 3.5.4(35), see A.9(35), see A.9(4).
Buffer_Type A.9.
by copy parameter passing 6.2.
by reference parameter passing 6.2.
by-copy type 6.2.
by-reference type 6.2.
atomic or volatile C.6.
Byte 3.5.4(36), see 13.3(80), see B.4(36), see 13.3(80), see B.4(29).
See storage element 13.3.
byte sex
See ordering of storage elements in a word 13.5.3.
Byte_Array B.4.
Byte_Mask 13.5.1.
ΓòÉΓòÉΓòÉ 33. index ΓòÉΓòÉΓòÉ
C 4.3.3(42), see B.3(77), see B.3.2(42), see B.3(77), see B.3.2(46).
child of Interfaces B.3.
C interface B.3.
C standard 1.2.
C_float B.3.
Calendar J.1.
child of Ada 9.6.
call 6.
call on a dispatching operation 3.9.2.
callable 9.9.
Callable attribute 9.9(2), see K(2), see K(23).
callable construct 6.
callable entity 6.
called partition E.4.
Caller attribute C.7.1(14), see K(14), see K(25).
calling convention 6.3.1(2), see B.1(2), see B.1(11).
Ada 6.3.1.
associated with a designated profile 3.10.
entry 6.3.1.
Intrinsic 6.3.1.
protected 6.3.1.
calling partition E.4.
calling stub E.4.
CAN A.3.3(6), see J.5(6), see J.5(4).
cancellation
of a delay_statement 9.6.
of an entry call 9.5.3.
cancellation of a remote subprogram call E.4.
canonical form A.5.3.
canonical semantics 11.6.
canonical-form representation A.5.3.
Car 3.10.1(19), see 3.10.1(21), see 12.5.4(19), see 3.10.1(21), see 12.5.4(10),
12.5.4.
Car_Name 3.10.1(20), see 12.5.4(20), see 12.5.4(10).
case insensitive 2.3.
case_statement 5.4.
used 5.1(5), see P(5), see P(1).
case_statement_alternative 5.4.
used 5.4(2), see P(2), see P(1).
cast
See type conversion 4.6.
See unchecked type conversion 13.9.
catch (an exception)
See handle 11.
categorization pragma E.2.
Remote_Call_Interface E.2.3.
Remote_Types E.2.2.
Shared_Passive E.2.1.
categorized library unit E.2.
catenation operator
See concatenation operator 4.4(1), see 4.5.3(1), see 4.5.3(3).
CCH A.3.3.
Cedilla A.3.3.
Ceiling attribute A.5.3(33), see K(33), see K(27).
ceiling priority
of a protected object D.3.
Ceiling_Check
[partial] C.3.1(11), see D.3(11), see D.3(13).
Cell 3.10.1(15), see 3.10.1(15), see 3.10.1(16).
Cent_Sign A.3.3.
change of representation 13.6.
char B.3.
char_array B.3.
CHAR_BIT B.3.
Char_Ptrs B.3.2.
Char_Star B.3.2.
Char_IO A.10.10.
character 2.1(2), see 3.5.2(2), see A.1(2), see 3.5.2(2), see A.1(35).
used 2.7(2), see P(2), see P(1).
character set 2.1.
character set standard
16-bit 1.2.
7-bit 1.2.
8-bit 1.2.
control functions 1.2.
character type 3.5.2(1), see N(1), see N(5).
character_literal 2.5.
used 3.5.1(4), see 4.1(2), see 4.1.3(4), see 4.1(2), see 4.1.3(3),
P.
Character_Mapping A.4.2.
Character_Mapping_Function A.4.2.
Character_Range A.4.2.
Character_Ranges A.4.2.
Character_Sequence A.4.2.
Character_Set A.4.2(4), see A.4.7(46), see B.5(4), see A.4.7(46), see B.5(11).
characteristics 7.3.
Characters
child of Ada A.3.1.
chars_ptr B.3.1.
check
language-defined 11.5(2), see 11.6(2), see 11.6(1).
check, language-defined
Access_Check 4.1(13), see 4.6(13), see 4.6(49).
Accessibility_Check 3.10.2(29), see 4.6(29), see 4.6(48),
6.5(17), see E.4(17), see E.4(18).
Ceiling_Check C.3.1(11), see D.3(11), see D.3(13).
Discriminant_Check 4.1.3(15), see 4.3(15), see 4.3(6),
4.3.2(8), 4.6(8), 4.6(43),
4.6(45), 4.6(45), 4.6(51),
4.6(52), 4.7(52), 4.7(4),
4.8.
Division_Check 3.5.4(20), see 4.5.5(20), see 4.5.5(22),
A.5.1(28), see A.5.3(28), see A.5.3(47),
G.1.1(40), see G.1.2(40), see G.1.2(28),
K.
Elaboration_Check 3.11.
Index_Check 4.1.1(7), 4.1.2(7), see 4.3.3(7), 4.1.2(7), see 4.3.3(29),
4.3.3(30), see 4.5.3(8), see 4.6(30), see 4.5.3(8), see 4.6(51),
4.7(4), 4.8(4), 4.8(10).
Length_Check 4.5.1(8), see 4.6(37), see 4.6(8), see 4.6(37), see 4.6(52).
Overflow_Check 3.5.4(20), see 4.4(20), see 4.4(11),
5.4(13), G.2.1(13), G.2.1(11),
G.2.2(7), G.2.3(7), G.2.3(25),
G.2.4(2), G.2.6(2), G.2.6(3).
Partition_Check E.4(19)
Range_Check 3.2.2(11), see 3.5(11), see 3.5(24),
3.5(27), 3.5(27), 3.5(43),
3.5(44), 3.5(44), 3.5(51),
3.5(55), 3.5.5(55), 3.5.5(7),
3.5.9(19), see 4.2(19), see 4.2(11),
4.3.3(28), see 4.5.1(28), see 4.5.1(8),
4.5.6(6), 4.5.6(6), 4.5.6(13),
4.6(28), 4.6(28), 4.6(38),
4.6(46), 4.6(46), 4.6(51),
4.7(4), 13.13.2(4), 13.13.2(35),
A.5.2(39), see A.5.2(39), see A.5.2(40),
A.5.3(26), see A.5.3(26), see A.5.3(29),
A.5.3(50), see A.5.3(50), see A.5.3(53),
A.5.3(59), see A.5.3(59), see A.5.3(62),
K(11), K(11), K(41),
K(47), K(47), K(114),
K(122), K(122), K(184),
K(220), K(220), K(241).
Reserved_Check C.3.1.
Storage_Check 11.1(6), 13.3(6), 13.3(67),
13.11(17), see D.7(17), see D.7(15).
Tag_Check 3.9.2(16), see 4.6(42), see 4.6(16), see 4.6(42), see 4.6(52),
5.2(10), 6.5(10), 6.5(9).
child
of a library unit 10.1.1.
choice parameter 11.2.
choice_parameter_specification 11.2.
used 11.2(3), see P(3), see P(1).
Circumflex A.3.3.
class N.
See also package 7.
See also tag 3.9.
of types 3.2.
Class attribute 3.9(14), see 7.3.1(9), see K(14), see 7.3.1(9), see K(31),
K.
class determined for a formal type 12.5.
class-wide type 3.4.1(4), see 3.7(4), see 3.7(26).
cleanup
See finalization 7.6.1.
clock 9.6(6), see 9.6(12), see D.8(6), see 9.6(12), see D.8(7).
clock jump D.8.
clock tick D.8.
Close 7.5(19), 7.5(20), A.8.1(19), 7.5(20), A.8.1(8),
A.8.4(8), see A.10.1(11), see A.12.1(8), see A.10.1(11), see A.12.1(10).
close result set G.2.3.
closed entry 9.5.3.
of a protected object 9.5.3.
of a task 9.5.3.
closed under derivation 3.4(28), see N(6), see N(28), see N(6), see N(41).
closure
downward 3.10.2.
COBOL B.4(104), see B.4(104), see B.4(113).
child of Interfaces B.4.
COBOL interface B.4.
COBOL standard 1.2.
COBOL_Character B.4.
COBOL_Employee_Record_Type B.4.
COBOL_Employee_IO B.4.
COBOL_Record B.4.
Code 4.7.
code_statement 13.8.
used 5.1(4), see P(4), see P(1).
coding
aspect of representation 13.4.
Coefficient 3.5.7.
Coin A.5.2(58)
Col A.10.1.
colon 2.1(15), see A.3.3(10), see J.5(15), see A.3.3(10), see J.5(6).
Color 3.2.1(15), see 3.5.1(15), see 3.5.1(14).
Column 3.2.1.
column number A.10.
Column_Ptr 3.5.4.
comma 2.1(15), see A.3.3(15), see A.3.3(8).
Command_Line
child of Ada A.15.
Command_Name A.15.
comment 2.7.
comments, instructions for submission Introduction.
Commercial_At A.3.3.
Communication_Error E.5.
comparison operator
See relational operator 4.5.2.
compatibility
composite_constraint with an access subtype 3.10.
constraint with a subtype 3.2.2.
delta_constraint with an ordinary fixed point subtype
J.3.
digits_constraint with a decimal fixed point subtype
3.5.9.
digits_constraint with a floating point subtype J.3.
discriminant constraint with a subtype 3.7.1.
index constraint with a subtype 3.6.1.
range with a scalar subtype 3.5.
range_constraint with a scalar subtype 3.5.
compatible
a type, with a convention B.1.
compilation 10.1.1.
separate 10.1.
Compilation unit 10.1(2), see 10.1.1(9), see N(2), see 10.1.1(9), see N(7).
compilation units needed
by a compilation unit 10.2.
remote call interface E.2.3.
shared passive library unit E.2.1.
compilation_unit 10.1.1.
used 10.1.1(2), see P(2), see P(1).
compile-time error 1.1.2(27), see 1.1.5(27), see 1.1.5(4).
compile-time semantics 1.1.2.
complete context 8.6.
completely defined 3.11.1.
completion
abnormal 7.6.1.
compile-time concept 3.11.1.
normal 7.6.1.
run-time concept 7.6.1.
completion and leaving (completed and left) 7.6.1.
completion legality
entry_body 9.5.2.
[partial] 3.10.1.
Complex 3.8(28), see B.5(9), see G.1.1(28), see B.5(9), see G.1.1(3).
Complex_Elementary_Functions
child of Ada.Numerics G.1.2.
Complex_Types
child of Ada.Numerics G.1.1.
Complex_IO
child of Ada.Text_IO G.1.3.
child of Ada.Wide_Text_IO G.1.4.
component 3.2(2), see 9.4(31), see 9.4(2), see 9.4(31), see 9.4(32).
component subtype 3.6.
component_choice_list 4.3.1.
used 4.3.1(4), see P(4), see P(1).
component_clause 13.5.1.
used 13.5.1(2), see P(2), see P(1).
component_declaration 3.8.
used 3.8(5), see 9.4(6), see P(5), see 9.4(6), see P(1).
component_definition 3.6.
used 3.6(3), see 3.6(5), see 3.8(6), see P(3), see 3.6(5), see 3.8(6), see P(1).
component_item 3.8.
used 3.8(4), see P(4), see P(1).
component_list 3.8.
used 3.8(3), see 3.8.1(3), see P(3), see 3.8.1(3), see P(1).
Component_Size attribute 13.3(69), see K(69), see K(36).
Component_Size clause 13.3(7), see 13.3(7), see 13.3(70).
components
of a record type 3.8.
Compose attribute A.5.3(24), see K(24), see K(38).
Compose_From_Cartesian G.1.1.
Compose_From_Polar G.1.1.
composite type 3.2(2), see N(2), see N(8).
composite_constraint 3.2.2.
used 3.2.2(5), see P(5), see P(1).
compound delimiter 2.2.
compound_statement 5.1.
used 5.1(3), see P(3), see P(1).
concatenation operator 4.4(1), see 4.5.3(1), see 4.5.3(3).
concrete subprogram
See nonabstract subprogram 3.9.3.
concrete type
See nonabstract type 3.9.3.
concurrent processing
See task 9.
condition 5.3.
used 5.3(2), 5.5(3), 5.7(2), 5.5(3), 5.7(2),
9.5.2(7), see 9.7.1(3), see P(7), see 9.7.1(3), see P(1).
See also exception 11.
conditional_entry_call 9.7.3.
used 9.7(2), see P(2), see P(1).
configuration
of the partitions of a program E.
configuration pragma 10.1.5.
Locking_Policy D.3.
Normalize_Scalars H.1.
Queuing_Policy D.4.
Restrictions 13.12.
Reviewable H.3.1.
Suppress 11.5.
Task_Dispatching_Policy D.2.2.
conformance 6.3.1.
of an implementation with the Standard 1.1.3.
See also full conformance, mode conformance,
subtype conformance, type conformance
Conjugate G.1.1(12), see G.1.1(12), see G.1.1(15).
consistency
among compilation units 10.1.4.
constant 3.3.
See also literal 4.2.
See also static 4.9.
result of a function_call 6.4.
constant object 3.3.
constant view 3.3.
Constants
child of Ada.Strings.Maps A.4.6.
constituent
of a construct 1.1.4.
constrained 3.2.
object 3.3.1(9), see 3.10(9), see 6.4.1(9), see 3.10(9), see 6.4.1(16).
subtype 3.2(9), 3.4(6), 3.5(9), 3.4(6), 3.5(7),
3.5.1(10), see 3.5.4(9), 3.5.4(10), see 3.5.4(9), 3.5.4(10),
3.5.7(11), see 3.5.9(13), see 3.5.9(11), see 3.5.9(13), see 3.5.9(16),
3.6(15), 3.6(16), 3.7(15), 3.6(16), 3.7(26),
3.9(15), 3.10(14), K(15), 3.10(14), K(33).
Constrained attribute 3.7.2(3), see J.4(2), see K(3), see J.4(2), see K(42).
constrained by its initial value 3.3.1(9), see 3.10(9), see 3.10(9).
[partial] 4.8.
constrained_array_definition 3.6.
used 3.6(2), see P(2), see P(1).
constraint 3.2.2.
used 3.2.2(3), see P(3), see P(1).
[partial] 3.2.
of a first array subtype 3.6.
of an object 3.3.1.
Constraint_Error A.1.
raised by failure of run-time check
3.2.2(12), 3.5(24), 3.5(12), 3.5(24), 3.5(27),
3.5(43), 3.5(44), 3.5(43), 3.5(44), 3.5(51),
3.5(55), 3.5.4(20), see 3.5.5(55), 3.5.4(20), see 3.5.5(7),
3.5.9(19), 3.9.2(16), see 4.1(19), 3.9.2(16), see 4.1(13),
4.1.1(7), 4.1.2(7), 4.1.3(7), 4.1.2(7), 4.1.3(15),
4.2(11), 4.3(6), 4.3.2(11), 4.3(6), 4.3.2(8),
4.3.3(31), 4.4(11), 4.5(31), 4.4(11), 4.5(10),
4.5(11), 4.5(12), 4.5.1(11), 4.5(12), 4.5.1(8),
4.5.3(8), 4.5.5(22), see 4.5.6(8), 4.5.5(22), see 4.5.6(6),
4.5.6(12), 4.5.6(13), see 4.6(12), 4.5.6(13), see 4.6(28),
4.6(57), 4.6(60), 4.7(57), 4.6(60), 4.7(4),
4.8(10), 5.2(10), 5.4(10), 5.2(10), 5.4(13),
6.5(9), 11.1(4), 11.4.1(9), 11.1(4), 11.4.1(14),
11.5(10), 13.9.1(9), see 13.13.2(10), 13.9.1(9), see 13.13.2(35),
A.4.3(109), see A.4.7(47), see A.5.1(109), see A.4.7(47), see A.5.1(28),
A.5.1(34), A.5.2(39), see A.5.2(34), A.5.2(39), see A.5.2(40),
A.5.3(26), A.5.3(29), see A.5.3(26), A.5.3(29), see A.5.3(47),
A.5.3(50), A.5.3(53), see A.5.3(50), A.5.3(53), see A.5.3(59),
A.5.3(62), A.15(14), B.3(62), A.15(14), B.3(53),
B.3(54), B.4(58), E.4(54), B.4(58), E.4(19),
G.1.1(40), G.1.2(28), see G.2.1(40), G.1.2(28), see G.2.1(12),
G.2.2(7), G.2.3(26), see G.2.4(7), G.2.3(26), see G.2.4(3),
G.2.6(4), K(11), K(4), K(11), K(41),
K(47), K(114), K(47), K(114), K(122),
K(184), K(202), K(184), K(202), K(220),
K(241), K(241), K(261).
Construct 1.1.4(16), see N(16), see N(9).
constructor
See initialization 3.3.1(19), see 7.6(19), see 7.6(1).
See initialization expression 3.3.1.
See Initialize 7.6.
See initialized alligator 4.8.
Consumer 9.11(5), see 9.11(5), see 9.11(6).
context free grammar
complete listing P.
cross reference P.
notation 1.1.4.
under Syntax heading 1.1.2.
context_clause 10.1.2.
used 10.1.1(3), see P(3), see P(1).
context_item 10.1.2.
used 10.1.2(2), see P(2), see P(1).
contiguous representation
[partial] 13.5.2(5), see 13.7.1(12), see 13.9(5), see 13.7.1(12), see 13.9(9),
13.9(17), 13.11(17), 13.11(16).
Continue D.11.
control character
See also format_effector 2.1.
See also other_control_function 2.1.
a category of Character A.3.2(22), see A.3.3(22), see A.3.3(4),
A.3.3.
Control_Set A.4.6.
Controlled 7.6.
aspect of representation 13.11.3.
Controlled pragma 13.11.3(3), see L(3), see L(7).
controlled type 7.6(2), see 7.6(9), see N(2), see 7.6(9), see N(10).
Controller 9.1.
controlling formal parameter 3.9.2.
controlling operand 3.9.2(2)
controlling result 3.9.2.
controlling tag
for a call on a dispatching operation 3.9.2.
controlling tag value 3.9.2.
for the expression in an assignment_statement 5.2.
convention 6.3.1(2), see B.1(2), see B.1(11).
aspect of representation B.1.
Convention pragma B.1(7), see L(7), see L(8).
conversion 4.6(1), see 4.6(1), see 4.6(28).
access 4.6(13), see 4.6(18), see 4.6(13), see 4.6(18), see 4.6(47).
arbitrary order 1.1.4.
array 4.6(9), see 4.6(9), see 4.6(36).
composite (non-array) 4.6(21), see 4.6(21), see 4.6(40).
enumeration 4.6(21), see 4.6(21), see 4.6(34).
numeric 4.6(8), see 4.6(8), see 4.6(29).
unchecked 13.9.
value 4.6.
view 4.6.
Conversion_Error B.4.
convertible 4.6.
required 3.7(16), see 3.7.1(9), see 4.6(16), see 3.7.1(9), see 4.6(11),
4.6(15), see 6.4.1(15), see 6.4.1(6).
Copy E.4.2(2), see E.4.2(2), see E.4.2(5).
copy back of parameters 6.4.1.
copy parameter passing 6.2.
Copy_Array B.3.2.
Copy_Sign attribute A.5.3(51), see K(51), see K(44).
Copy_Terminated_Array B.3.2.
Copyright_Sign A.3.3.
core language 1.1.2.
corresponding constraint 3.4.
corresponding discriminants 3.7.
corresponding index
for an array_aggregate 4.3.3.
corresponding subtype 3.4.
corresponding value
of the target type of a conversion 4.6.
Cos A.5.1(5), see G.1.2(5), see G.1.2(4).
Cosh A.5.1(7), see G.1.2(7), see G.1.2(6).
Cot A.5.1(5), see G.1.2(5), see G.1.2(4).
Coth A.5.1(7), see G.1.2(7), see G.1.2(6).
Count A.4.3(13), see A.4.3(14), see A.4.3(13), see A.4.3(14), see A.4.3(15),
A.4.4(48), see A.4.4(49), see A.4.4(48), see A.4.4(49), see A.4.4(50),
A.4.5(43), see A.4.5(44), see A.4.5(43), see A.4.5(44), see A.4.5(45),
A.8.4(4), A.10(10), A.10.1(4), A.10(10), A.10.1(5),
A.12.1.
Count attribute 9.9(5), see K(5), see K(48).
Counter 3.4.
cover
a type 3.4.1.
of a choice and an exception 11.2.
cover a value
by a discrete_choice_list 3.8.1.
by a discrete_choice 3.8.1.
CPU_Identifier 7.4.
CR A.3.3.
create 3.1(12), A.8.1(6), see A.8.4(12), A.8.1(6), see A.8.4(6),
A.10.1(9), see A.12.1(9), see A.12.1(8).
creation
of a protected object C.3.1.
of a task object D.1.
of an object 3.3.
critical section
See intertask communication 9.5.
CSI A.3.3.
Currency_Sign A.3.3.
current column number A.10.
current index
of an open direct file A.8.
current instance
of a generic unit 8.6.
of a type 8.6.
current line number A.10.
current mode
of an open file A.7.
current page number A.10.
current size
of an external file A.8.
Current_Error A.10.1(17), see A.10.1(17), see A.10.1(20).
Current_Handler C.3.2.
Current_Input A.10.1(17), see A.10.1(17), see A.10.1(20).
Current_Output A.10.1(17), see A.10.1(17), see A.10.1(20).
Current_State D.10.
Current_Task C.7.1.
ΓòÉΓòÉΓòÉ 34. index ΓòÉΓòÉΓòÉ
dangling references
prevention via accessibility rules 3.10.2.
Data_Error A.8.1(15), A.8.4(18), A.9(15), A.8.4(18), A.9(9),
A.10.1(85), see A.12.1(26), see A.13(85), see A.12.1(26), see A.13(4).
Date 3.8.
Day 3.5.1(14), see 9.6(14), see 9.6(13).
Day_Duration 9.6.
Day_Number 9.6.
DC1 A.3.3.
DC2 A.3.3(6), see J.5(6), see J.5(4).
DC3 A.3.3.
DC4 A.3.3(6), see J.5(6), see J.5(4).
DCS A.3.3.
Deallocate 13.11.
deallocation of storage 13.11.2.
Decimal
child of Ada F.2.
decimal digit
a category of Character A.3.2.
decimal fixed point type 3.5.9(1), see 3.5.9(1), see 3.5.9(6).
Decimal_Conversions B.4.
Decimal_Digit_Set A.4.6.
Decimal_Element B.4.
decimal_fixed_point_definition 3.5.9.
used 3.5.9(2), see P(2), see P(1).
decimal_literal 2.4.1.
used 2.4(2), see P(2), see P(1).
Decimal_Output F.3.3.
Decimal_IO A.10.1.
Declaration 3.1(5), see 3.1(6), see N(5), see 3.1(6), see N(11).
declarative region
of a construct 8.1.
declarative_item 3.11.
used 3.11(2), see P(2), see P(1).
declarative_part 3.11.
used 5.6(2), see 6.3(2), 7.2(2), see 6.3(2), 7.2(2),
9.1(6), see 9.5.2(5), see P(6), see 9.5.2(5), see P(1).
declare 3.1(8), see 3.1(8), see 3.1(12).
declared pure 10.2.1.
Decrement B.3.2.
deeper
accessibility level 3.10.2.
statically 3.10.2(4), see 3.10.2(4), see 3.10.2(17).
default entry queuing policy 9.5.3.
default treatment C.3.
Default_Bit_Order 13.7.
Default_Currency F.3.3.
default_expression 3.7.
used 3.7(5), 3.8(6), see 6.1(5), 3.8(6), see 6.1(15),
12.4(2), see P(2), see P(1).
Default_Fill F.3.3.
Default_Message_Procedure 3.10.
default_name 12.6.
used 12.6(3), see P(3), see P(1).
Default_Priority 13.7(17), see D.1(17), see D.1(11).
Default_Radix_Mark F.3.3.
Default_Separator F.3.3.
deferred constant 7.4.
deferred constant declaration 3.3.1(6), see 7.4(6), see 7.4(2).
defining name 3.1.
defining_character_literal 3.5.1.
used 3.5.1(3), see P(3), see P(1).
defining_designator 6.1.
used 6.1(4), see 12.3(2), see P(4), see 12.3(2), see P(1).
defining_identifier 3.1.
used 3.2.1(3), 3.2.2(2), 3.3.1(3), 3.2.2(2), 3.3.1(3),
3.5.1(3), 3.10.1(2), see 5.5(3), 3.10.1(2), see 5.5(4),
6.1(7), 7.3(2), 7.3(7), 7.3(2), 7.3(3),
8.5.1(2), 8.5.2(2), 9.1(2), 8.5.2(2), 9.1(2),
9.1(3), 9.1(6), 9.4(3), 9.1(6), 9.4(2),
9.4(3), 9.4(7), 9.5.2(3), 9.4(7), 9.5.2(2),
9.5.2(5), 9.5.2(8), 10.1.3(5), 9.5.2(8), 10.1.3(4),
10.1.3(5), see 10.1.3(6), see 11.2(5), see 10.1.3(6), see 11.2(4),
12.5(2), 12.7(2), P(2), 12.7(2), P(1).
defining_identifier_list 3.3.1.
used 3.3.1(2), see 3.3.2(2), see 3.7(2), see 3.3.2(2), see 3.7(5),
3.8(6), 6.1(15), 11.1(6), 6.1(15), 11.1(2),
12.4(2), P(2), P(1).
defining_operator_symbol 6.1.
used 6.1(6), see P(6), see P(1).
defining_program_unit_name 6.1.
used 6.1(4), 6.1(6), 7.1(4), 6.1(6), 7.1(3),
7.2(2), 8.5.3(2), see 8.5.5(2), 8.5.3(2), see 8.5.5(2),
12.3(2), see P(2), see P(1).
Definite attribute 12.5.1(23), see K(23), see K(50).
definite subtype 3.3.
Definition 3.1(7), see N(7), see N(12).
Deg_To_Rad 4.9.
Degree_Sign A.3.3.
DEL A.3.3(14), see J.5(14), see J.5(4).
delay_alternative 9.7.1.
used 9.7.1(4), see 9.7.2(2), see P(4), see 9.7.2(2), see P(1).
delay_relative_statement 9.6.
used 9.6(2), see P(2), see P(1).
delay_statement 9.6.
used 5.1(4), see 9.7.1(6), see 9.7.4(4), see 9.7.1(6), see 9.7.4(4),
P.
delay_until_statement 9.6.
used 9.6(2), see P(2), see P(1).
Delete A.4.3(29), see A.4.3(30), see A.4.4(29), see A.4.3(30), see A.4.4(64),
A.4.4(65), see A.4.5(59), see A.4.5(65), see A.4.5(59), see A.4.5(60),
A.8.1(8), A.8.4(8), A.10.1(8), A.8.4(8), A.10.1(11),
A.12.1.
delimiter 2.2.
delivery
of an interrupt C.3.
delta
of a fixed point type 3.5.9.
Delta attribute 3.5.10(3), see K(3), see K(52).
delta_constraint J.3.
used 3.2.2(6), see P(6), see P(1).
Denorm attribute A.5.3(9), see K(9), see K(54).
denormalized number A.5.3.
denote 8.6.
informal definition 3.1.
name used as a pragma argument 8.6.
depend on a discriminant
for a constraint or component_definition 3.7.
for a component 3.7.
dependence
elaboration 10.2.
of a task on a master 9.3.
of a task on another task 9.3.
semantic 10.1.1.
depth
accessibility level 3.10.2.
dereference 4.1.
Dereference_Error B.3.1.
derivation class
for a type 3.4.1.
derived from
directly or indirectly 3.4.1.
derived type 3.4(1), see N(1), see N(13).
[partial] 3.4.
derived_type_definition 3.4.
used 3.2.1(4), see P(4), see P(1).
descendant 10.1.1.
of a type 3.4.1.
relationship with scope 8.2.
Descriptor 13.6.
designate 3.10.
designated profile
of an access-to-subprogram type 3.10.
designated subtype
of a named access type 3.10.
of an anonymous access type 3.10.
designated type
of a named access type 3.10.
of an anonymous access type 3.10.
designator 6.1.
used 6.3(2), see P(2), see P(1).
destructor
See finalization 7.6(1), see 7.6.1(1), see 7.6.1(1).
Detach_Handler C.3.2.
determined class for a formal type 12.5.
determines
a type by a subtype_mark 3.2.2.
Device 3.8.1.
Device_Error A.8.1(15), A.8.4(15), A.8.4(18),
A.10.1(85), see A.12.1(26), see A.13(85), see A.12.1(26), see A.13(4).
Device_Interface C.3.2.
Device_Priority C.3.2.
Diaeresis A.3.3.
Dice A.5.2.
Dice_Game A.5.2.
Die A.5.2.
digit 2.1.
used 2.1(3), 2.3(3), see 2.4.1(3), 2.3(3), see 2.4.1(3),
2.4.2(5), see P(5), see P(1).
digits
of a decimal fixed point subtype 3.5.9,
3.5.10.
Digits attribute 3.5.8(2), see 3.5.10(2), see 3.5.10(7),
K(56), K(56), K(58).
digits_constraint 3.5.9.
used 3.2.2(6), see P(6), see P(1).
dimensionality
of an array 3.6.
direct access A.8.
direct file A.8.
direct_name 4.1.
used 3.8.1(2), see 4.1(2), 5.1(2), see 4.1(2), 5.1(8),
9.5.2(3), see 13.1(3), see J.7(3), see 13.1(3), see J.7(1),
P.
Direct_IO J.1.
child of Ada A.8.4(2), see A.9(2), see A.9(3).
Direction A.4.1.
directly specified
of an aspect of representation of an entity 13.1.
directly visible 8.3(2), see 8.3(2), see 8.3(21).
within a pragma in a context_clause 10.1.6.
within a pragma that appears at the place of a compilation unit
10.1.6.
within a use_clause in a context_clause 10.1.6.
within a with_clause 10.1.6.
within the parent_unit_name of a library unit 10.1.6.
within the parent_unit_name of a subunit 10.1.6.
Discard_Names pragma C.5(3), see L(3), see L(9).
discontiguous representation
partial 13.5.2(5), see 13.7.1(12), see 13.9(5), see 13.7.1(12), see 13.9(9),
13.9(17), 13.11(17), 13.11(16).
discrete array type 4.5.2.
discrete type 3.2(3), see 3.5(1), see N(3), see 3.5(1), see N(14).
discrete_choice 3.8.1.
used 3.8.1(4), see P(4), see P(1).
discrete_choice_list 3.8.1.
used 3.8.1(3), see 4.3.3(5), see 5.4(3), see 4.3.3(5), see 5.4(3),
P.
Discrete_Random
child of Ada.Numerics A.5.2.
discrete_range 3.6.1.
used 3.6.1(2), see 3.8.1(5), see 4.1.2(2), see 3.8.1(5), see 4.1.2(2),
P.
discrete_subtype_definition 3.6.
used 3.6(5), 5.5(4), see 9.5.2(5), 5.5(4), see 9.5.2(2),
9.5.2(8), see P(8), see P(1).
discriminant 3.2(5), see 3.7(1), see N(5), see 3.7(1), see N(15).
of a variant_part 3.8.1.
discriminant_association 3.7.1.
used 3.7.1(2), see P(2), see P(1).
Discriminant_Check 11.5.
[partial] 4.1.3(15), see 4.3(6), 4.3.2(15), see 4.3(6), 4.3.2(8),
4.6(43), 4.6(45), see 4.6(43), 4.6(45), see 4.6(51),
4.6(52), 4.7(4), 4.8(52), 4.7(4), 4.8(10).
discriminant_constraint 3.7.1.
used 3.2.2(7), see P(7), see P(1).
discriminant_part 3.7.
used 3.10.1(2), see 7.3(2), see 7.3(2), see 7.3(2), see 7.3(3),
12.5(2), P(2), P(1).
discriminant_specification 3.7.
used 3.7(4), see P(4), see P(1).
discriminants
known 3.7.
unknown 3.7.
discriminated type 3.7.
Disk_Unit 3.8.1.
dispatching 3.9.
dispatching call
on a dispatching operation 3.9.2.
dispatching operation 3.9.2(1), see 3.9.2(1), see 3.9.2(2).
[partial] 3.9.
dispatching point D.2.1.
[partial] D.2.1(8), see D.2.2(8), see D.2.2(12).
dispatching policy for tasks
[partial] D.2.1.
dispatching, task D.2.1.
Display_Format B.4.
displayed magnitude (of a decimal value) F.3.2.
disruption of an assignment 9.8(21), see 13.9.1(21), see 13.9.1(5).
[partial] 11.6.
distinct access paths 6.2.
distributed program E.
distributed system E.
distributed systems C.
divide 2.1(15), see F.2(15), see F.2(6).
divide operator 4.4(1), see 4.5.5(1), see 4.5.5(1).
Dividend_Type F.2.
Division_Check 11.5.
[partial] 3.5.4(20), see 4.5.5(20), see 4.5.5(22),
A.5.1(28), see A.5.3(28), see A.5.3(47),
G.1.1(40), see G.1.2(40), see G.1.2(28),
K.
Division_Sign A.3.3.
Divisor_Type F.2.
DLE A.3.3(6), see J.5(6), see J.5(4).
Do_APC E.5.
Do_RPC E.5.
documentation (required of an implementation) 1.1.3,
M.
documentation requirements 1.1.2(34), see 1.1.3(34), see 1.1.3(18),
13.11(22), see A.5.2(22), see A.5.2(44),
A.13(15), C.1(15), C.1(6),
C.3(12), C.3.2(12), C.3.2(24),
C.4(12), C.7.1(12), C.7.1(19),
C.7.2(18), see D.2.2(18), see D.2.2(14),
D.6(3), D.8(3), D.8(33),
D.9(7), D.12(7), D.12(5),
E.5(25), H.1(25), H.1(5),
H.2(1), H.3.2(1), H.3.2(8),
H.4(25), J.7.1(25), J.7.1(12).
Dollar_Sign A.3.3.
Done J.7.1.
dot 2.1.
dot selection
See selected_component 4.1.3.
Dot_Product 6.1(39), see 6.3(39), see 6.3(11).
double B.3.
Double_Precision B.5.
Double_Square 3.7.
downward closure 3.10.2.
Dozen 4.6.
drift rate D.8.
Drum_Ref 3.10.
Drum_Unit 3.8.1.
Duration A.1.
dynamic binding
See dispatching operation 3.9.
dynamic semantics 1.1.2.
Dynamic_Priorities
child of Ada D.5.
dynamically determined tag 3.9.2.
dynamically enclosing
of one execution by another 11.4.
dynamically tagged 3.9.2.
ΓòÉΓòÉΓòÉ 35. index ΓòÉΓòÉΓòÉ
e A.5.
edited output F.3.
Editing
child of Ada.Text_IO F.3.3.
child of Ada.Wide_Text_IO F.3.4.
effect
external 1.1.3.
efficiency 11.5(29), see 11.6(29), see 11.6(1).
Elaborate pragma 10.2.1(20), see L(20), see L(10).
Elaborate_All pragma 10.2.1(21), see L(21), see L(11).
Elaborate_Body pragma 10.2.1(22), see L(22), see L(12).
elaborated 3.11.
elaboration 3.1(11), see N(11), see N(19).
abstract_subprogram_declaration 6.1.
access_definition 3.10.
access_type_definition 3.10.
array_type_definition 3.6.
choice_parameter_specification 11.4.
component_declaration 3.8.
component_definition 3.6(22), see 3.8(22), see 3.8(18).
component_list 3.8.
declaration named by a pragma Import B.1.
declarative_part 3.11.
deferred constant declaration 7.4.
delta_constraint J.3.
derived_type_definition 3.4.
digits_constraint 3.5.9.
discrete_subtype_definition 3.6.
discriminant_constraint 3.7.1.
entry_declaration 9.5.2.
enumeration_type_definition 3.5.1.
exception_declaration 11.1.
fixed_point_definition 3.5.9.
floating_point_definition 3.5.7.
full type definition 3.2.1.
full_type_declaration 3.2.1.
generic body 12.2.
generic_declaration 12.1.
generic_instantiation 12.3.
incomplete_type_declaration 3.10.1.
index_constraint 3.6.1.
integer_type_definition 3.5.4.
loop_parameter_specification 5.5.
non-generic subprogram_body 6.3.
nongeneric package_body 7.2.
number_declaration 3.3.2.
object_declaration 3.3.1(15), see 7.6(15), see 7.6(10).
package_body of Standard A.1.
package_declaration 7.1.
partition E.1(6), see E.5(6), see E.5(21).
pragma 2.8.
private_extension_declaration 7.3.
private_type_declaration 7.3.
protected declaration 9.4.
protected_body 9.4.
protected_definition 9.4.
range_constraint 3.5.
real_type_definition 3.5.6.
record_definition 3.8.
record_extension_part 3.9.1.
record_type_definition 3.8.
renaming_declaration 8.5.
representation_clause 13.1.
single_protected_declaration 9.4.
single_task_declaration 9.1.
Storage_Size pragma 13.3.
subprogram_declaration 6.1.
subtype_declaration 3.2.2.
subtype_indication 3.2.2.
task declaration 9.1.
task_body 9.1.
task_definition 9.1.
use_clause 8.4.
variant_part 3.8.1.
elaboration control 10.2.1.
elaboration dependence
library_item on another 10.2.
Elaboration_Check 11.5.
[partial] 3.11.
Elem 12.1.
element A.4.4(26), see A.4.5(20), see B.3.2(26), see A.4.5(20), see B.3.2(4).
of a storage pool 13.11.
Element_Array B.3.2.
Element_Type 3.9.3(15), see A.8.1(2), see A.8.4(15), see A.8.1(2), see A.8.4(2),
A.9.
elementary type 3.2(2), see N(2), see N(16).
Elementary_Functions
child of Ada.Numerics A.5.1.
eligible
a type, for a convention B.1.
else part
of a selective_accept 9.7.1.
EM A.3.3.
embedded systems C(1), see D(1), see D(1).
Empty 3.9.3.
encapsulation
See package 7.
enclosing
immediately 8.1.
end of a line 2.2.
End_Error A.8.1(15), A.8.4(18), see A.10.1(15), A.8.4(18), see A.10.1(85),
A.12.1(26), see A.13(26), see A.13(4).
End_Of_File 11.4.2(4), A.8.1(13), see A.8.4(4), A.8.1(13), see A.8.4(16),
A.10.1(34), see A.12.1(34), see A.12.1(12).
End_Of_Line A.10.1.
End_Of_Page A.10.1.
endian
big 13.5.3.
little 13.5.3.
ENQ A.3.3.
entity
[partial] 3.1.
entry
closed 9.5.3.
open 9.5.3.
single 9.5.2.
entry call 9.5.3.
simple 9.5.3.
entry calling convention 6.3.1.
entry family 9.5.2.
entry index subtype 3.8(18), see 9.5.2(18), see 9.5.2(20).
entry queue 9.5.3.
entry queuing policy 9.5.3.
default policy 9.5.3.
entry_barrier 9.5.2.
used 9.5.2(5), see P(5), see P(1).
entry_body 9.5.2.
used 9.4(8), see P(8), see P(1).
entry_body_formal_part 9.5.2.
used 9.5.2(5), see P(5), see P(1).
entry_call_alternative 9.7.2.
used 9.7.2(2), see 9.7.3(2), see P(2), see 9.7.3(2), see P(1).
entry_call_statement 9.5.3.
used 5.1(4), see 9.7.2(3), see 9.7.4(4), see 9.7.2(3), see 9.7.4(4),
P.
entry_declaration 9.5.2.
used 9.1(5), see 9.4(5), see P(5), see 9.4(5), see P(1).
entry_index 9.5.2.
used 9.5.2(3), see P(3), see P(1).
entry_index_specification 9.5.2.
used 9.5.2(6), see P(6), see P(1).
Enum 12.5(13), see A.10.1(13), see A.10.1(79).
Enum_IO 8.5.5.
enumeration literal 3.5.1.
enumeration type 3.2(3), see 3.5.1(1), see N(3), see 3.5.1(1), see N(17).
enumeration_aggregate 13.4.
used 13.4(2), see P(2), see P(1).
enumeration_literal_specification 3.5.1.
used 3.5.1(2), see P(2), see P(1).
enumeration_representation_clause 13.4.
used 13.1(2), see P(2), see P(1).
enumeration_type_definition 3.5.1.
used 3.2.1(4), see P(4), see P(1).
Enumeration_IO A.10.1.
environment declarative_part 10.1.4.
for the environment task of a partition 10.2.
environment 10.1.4.
environment task 10.2.
EOF 8.5.2.
EOT A.3.3(5), see J.5(5), see J.5(4).
EPA A.3.3.
epoch D.8.
equal operator 4.4(1), see 4.5.2(1), see 4.5.2(1).
equality operator 4.5.2.
special inheritance rule for tagged types 3.4,
4.5.2.
equals sign 2.1.
Equals_Sign A.3.3.
erroneous execution 1.1.2(32), 1.1.5(32), 1.1.5(10),
3.7.2(4), 9.8(4), 9.8(21),
9.10(11), 11.5(11), 11.5(26),
13.3(13), 13.3(13), 13.3(27),
13.9.1(8), 13.9.1(8), 13.9.1(12),
13.11(21), 13.11.2(21), 13.11.2(16),
A.10.3(22), see A.13(22), see A.13(17),
B.3.1(51), B.3.2(51), B.3.2(35),
C.3.1(14), C.7.1(14), C.7.1(18),
C.7.2(14), D.5(14), D.5(12),
D.11(9), H.4(9), H.4(26).
error 11.1.
compile-time 1.1.2(27), see 1.1.5(27), see 1.1.5(4).
link-time 1.1.2(29), see 1.1.5(29), see 1.1.5(4).
run-time 1.1.2(30), see 1.1.5(6), see 11.5(30), see 1.1.5(6), see 11.5(2),
11.6.
See also bounded error, erroneous execution
ESA A.3.3.
ESC A.3.3.
Establish_RPC_Receiver E.5.
ETB A.3.3.
ETX A.3.3.
evaluation 3.1(11), see N(11), see N(19).
aggregate 4.3.
allocator 4.8.
array_aggregate 4.3.3.
attribute_reference 4.1.4.
concatenation 4.5.3.
dereference 4.1.
discrete_range 3.6.1.
extension_aggregate 4.3.2.
generic_association 12.3.
generic_association for a formal object of mode in
12.4.
indexed_component 4.1.1.
initialized allocator 4.8.
membership test 4.5.2.
name 4.1.
name that has a prefix 4.1.
null literal 4.2.
numeric literal 4.2.
parameter_association 6.4.1.
prefix 4.1.
primary that is a name 4.4.
qualified_expression 4.7.
range 3.5.
range_attribute_reference 4.1.4.
record_aggregate 4.3.1.
record_component_association_list 4.3.1.
selected_component 4.1.3.
short-circuit control form 4.5.1.
slice 4.1.2.
string_literal 4.2.
uninitialized allocator 4.8.
Val 3.5.5(7), see K(7), see K(261).
Value 3.5.
value conversion 4.6.
view conversion 4.6.
Wide_Value 3.5.
Exception 11(1), see 11.1(1), see N(1), see 11.1(1), see N(18).
exception occurrence 11.
exception_choice 11.2.
used 11.2(3), see P(3), see P(1).
exception_declaration 11.1.
used 3.1(3), see P(3), see P(1).
exception_handler 11.2.
used 11.2(2), see P(2), see P(1).
Exception_Identity 11.4.1.
Exception_Information 11.4.1.
Exception_Message 11.4.1.
Exception_Name 11.4.1(2), see 11.4.1(2), see 11.4.1(5).
Exception_Occurrence 11.4.1.
Exception_Occurrence_Access 11.4.1.
exception_renaming_declaration 8.5.2.
used 8.5(2), see P(2), see P(1).
Exception_Id 11.4.1.
Exceptions
child of Ada 11.4.1.
Exchange 12.1(21), see 12.2(21), see 12.2(5).
Exchange_Handler C.3.2.
Exclam J.5.
Exclamation A.3.3.
execution 3.1(11), see N(11), see N(19).
abort_statement 9.8.
aborting the execution of a construct 9.8.
accept_statement 9.5.2.
Ada program 9.
assignment_statement 5.2(7), see 7.6(7), see 7.6(17),
7.6.1.
asynchronous_select with a delay_statement trigger
9.7.4.
asynchronous_select with an entry call trigger 9.7.4.
block_statement 5.6.
call on a dispatching operation 3.9.2.
call on an inherited subprogram 3.4.
case_statement 5.4.
conditional_entry_call 9.7.3.
delay_statement 9.6.
dynamically enclosing 11.4.
entry_body 9.5.2.
entry_call_statement 9.5.3.
exit_statement 5.7.
goto_statement 5.8.
handled_sequence_of_statements 11.2.
handler 11.4.
if_statement 5.3.
instance of Unchecked_Deallocation 7.6.1.
loop_statement 5.5.
loop_statement with a for iteration_scheme 5.5.
loop_statement with a while iteration_scheme 5.5.
null_statement 5.1.
partition 10.2.
pragma 2.8.
program 10.2.
protected subprogram call 9.5.1.
raise_statement with an exception_name 11.3.
re-raise statement 11.3.
remote subprogram call E.4.
requeue protected entry 9.5.4.
requeue task entry 9.5.4.
requeue_statement 9.5.4.
return_statement 6.5.
selective_accept 9.7.1.
sequence_of_statements 5.1.
subprogram call 6.4.
subprogram_body 6.3.
task 9.2.
task_body 9.2.
timed_entry_call 9.7.2.
execution resource
associated with a protected object 9.4.
required for a task to run 9.
exit_statement 5.7.
used 5.1(4), see P(4), see P(1).
Exp A.5.1(4), see B.1(51), see G.1.2(4), see B.1(51), see G.1.2(3).
expanded name 4.1.3.
Expanded_Name 3.9.
expected profile 8.6.
accept_statement entry_direct_name 9.5.2.
Access attribute_reference prefix 3.10.2.
attribute_definition_clause name 13.3.
character_literal 4.2.
formal subprogram actual 12.6.
formal subprogram default_name 12.6.
subprogram_renaming_declaration 8.5.4.
expected type 8.6.
abort_statement task_name 9.8.
access attribute_reference 3.10.2.
actual parameter 6.4.1.
aggregate 4.3.
allocator 4.8.
array_aggregate 4.3.3.
array_aggregate component expression 4.3.3.
array_aggregate discrete_choice 4.3.3.
assignment_statement expression 5.2.
assignment_statement variable_name 5.2.
attribute_definition_clause expression or name 13.3.
attribute_designator expression 4.1.4.
case expression 5.4.
case_statement_alternative discrete_choice 5.4.
character_literal 4.2.
code_statement 13.8.
component_clause expressions 13.5.1.
component_declaration default_expression 3.8.
condition 5.3.
decimal fixed point type digits 3.5.9.
delay_relative_statement expression 9.6.
delay_until_statement expression 9.6.
delta_constraint expression J.3.
dereference name 4.1.
discrete_subtype_definition range 3.6.
discriminant default_expression 3.7.
discriminant_association expression 3.7.1.
entry_index 9.5.2.
enumeration_representation_clause expressions 13.4.
extension_aggregate 4.3.2.
extension_aggregate ancestor expression 4.3.2.
first_bit 13.5.1.
fixed point type delta 3.5.9.
generic formal in object actual 12.4.
generic formal object default_expression 12.4.
index_constraint discrete_range 3.6.1.
indexed_component expression 4.1.1.
Interrupt_Priority pragma argument D.1.
last_bit 13.5.1.
link name B.1.
membership test simple_expression 4.5.2.
modular_type_definition expression 3.5.4.
null literal 4.2.
number_declaration expression 3.3.2.
object_declaration initialization expression 3.3.1.
parameter default_expression 6.1.
position 13.5.1.
Priority pragma argument D.1.
range simple_expressions 3.5.
range_attribute_designator expression 4.1.4.
range_constraint range 3.5.
real_range_specification bounds 3.5.7.
record_aggregate 4.3.1.
record_component_association expression 4.3.1.
requested decimal precision 3.5.7.
restriction parameter expression 13.12.
return expression 6.5.
short-circuit control form relation 4.5.1.
signed_integer_type_definition simple_expression
3.5.4.
slice discrete_range 4.1.2.
Storage_Size pragma argument 13.3.
string_literal 4.2.
type_conversion operand 4.6(6)
variant_part discrete_choice 3.8.1.
expiration time
[partial] 9.6.
for a delay_relative_statement 9.6.
for a delay_until_statement 9.6.
explicit declaration 3.1(5), see N(5), see N(11).
explicit initial value 3.3.1.
explicit_actual_parameter 6.4.
used 6.4(5), see P(5), see P(1).
explicit_dereference 4.1.
used 4.1(2), see P(2), see P(1).
explicit_generic_actual_parameter 12.3.
used 12.3(4), see P(4), see P(1).
explicitly assign 10.2.
exponent 2.4.1(4), see 4.5.6(4), see 4.5.6(11).
used 2.4.1(2), see 2.4.2(2), see P(2), see 2.4.2(2), see P(1).
Exponent attribute A.5.3(18), see K(18), see K(60).
exponentiation operator 4.4(1), see 4.5.6(1), see 4.5.6(7).
Export pragma B.1(6), see L(6), see L(13).
exported
aspect of representation B.1.
exported entity B.1.
Expr_Ptr 3.9.1.
expression 3.9(33), see 4.4(1), see 4.4(33), see 4.4(1), see 4.4(2).
used 2.8(3), 3.3.1(2), see 3.3.2(3), 3.3.1(2), see 3.3.2(2),
3.5.4(4), see 3.5.7(2), see 3.5.9(4), see 3.5.7(2), see 3.5.9(3),
3.5.9(4), see 3.5.9(5), see 3.7(4), see 3.5.9(5), see 3.7(6),
3.7.1(3), see 3.8.1(5), see 4.1.1(3), see 3.8.1(5), see 4.1.1(2),
4.1.4(3), see 4.1.4(5), see 4.3.1(3), see 4.1.4(5), see 4.3.1(4),
4.3.2(3), see 4.3.3(3), see 4.3.3(3), see 4.3.3(3), see 4.3.3(5),
4.4(7), 4.6(2), 4.7(7), 4.6(2), 4.7(2),
5.2(2), 5.3(3), 5.4(2), 5.3(3), 5.4(2),
6.4(6), 6.5(2), 9.5.2(6), 6.5(2), 9.5.2(4),
9.6(3), 9.6(4), 12.3(3), 9.6(4), 12.3(5),
13.3(2), 13.3(63), see 13.5.1(2), 13.3(63), see 13.5.1(4),
13.12(4), see B.1(5), B.1(4), see B.1(5), B.1(6),
B.1(8), B.1(10), C.3.1(8), B.1(10), C.3.1(4),
D.1(3), D.1(5), J.3(3), D.1(5), J.3(2),
J.7(1), J.8(1), L(1), J.8(1), L(6),
L(13), L(14), L(13), L(14), L(18),
L(19), L(27), L(19), L(27), L(35),
P.
extended_digit 2.4.2.
used 2.4.2(4), see P(4), see P(1).
extension
of a private type 3.9(2), see 3.9.1(2), see 3.9.1(1).
of a record type 3.9(2), see 3.9.1(2), see 3.9.1(1).
of a type 3.9(2), see 3.9.1(2), see 3.9.1(1).
extension_aggregate 4.3.2.
used 4.3(2), see P(2), see P(1).
external call 9.5.
external effect
of the execution of an Ada program 1.1.3.
volatile/atomic objects C.6.
external file A.7.
external interaction 1.1.3.
external name B.1.
external requeue 9.5.
External_Tag 3.9.
External_Tag attribute 13.3(75), see K(75), see K(64).
External_Tag clause 13.3(7), see 13.3(75), see K(7), see 13.3(75), see K(65).
extra permission to avoid raising exceptions 11.6.
extra permission to reorder actions 11.6.
ΓòÉΓòÉΓòÉ 36. index ΓòÉΓòÉΓòÉ
factor 4.4.
used 4.4(5), see P(5), see P(1).
failure A.15.
of a language-defined check 11.5.
False 3.5.3.
family
entry 9.5.2.
Feminine_Ordinal_Indicator A.3.3.
FF A.3.3(5), see J.5(5), see J.5(4).
Field A.10.1.
file
as file object A.7.
file terminator A.10.
File_Access A.10.1.
File_Descriptor 7.5.
File_Handle 11.4.2.
File_Mode A.8.1(4), see A.8.4(4), see A.10.1(4), see A.8.4(4), see A.10.1(4),
A.12.1.
File_Name 7.3(22), see 7.5(18), see 7.5(22), see 7.5(18), see 7.5(19).
File_Not_Found 11.4.2.
File_System 11.4.2(2), see 11.4.2(2), see 11.4.2(6).
File_Type A.8.1(3), see A.8.4(3), see A.10.1(3), see A.8.4(3), see A.10.1(3),
A.12.1.
Finalization
child of Ada 7.6.
of a master 7.6.1.
of a protected object 9.4(20), see C.3.1(20), see C.3.1(12).
of a task object J.7.1.
of an object 7.6.1.
Finalize 7.6(2), see 7.6(6), see 7.6(2), see 7.6(6), see 7.6(8).
Find E.4.2.
Find_Token A.4.3(16), see A.4.4(51), see A.4.5(16), see A.4.4(51), see A.4.5(46).
Fine_Delta 13.7.
named number in package System 13.7.
First attribute 3.5(12), see 3.6.2(3), see K(12), see 3.6.2(3), see K(68),
K.
first subtype 3.2.1(6), see 3.4.1(6), see 3.4.1(5).
First(N) attribute 3.6.2(4), see K(4), see K(66).
first_bit 13.5.1.
used 13.5.1(3), see P(3), see P(1).
First_Bit attribute 13.5.2(3), see K(3), see K(72).
Fixed
child of Ada.Strings A.4.3.
fixed point type 3.5.9.
fixed_point_definition 3.5.9.
used 3.5.6, P(1)
Fixed_IO A.10.1.
Flip_A_Coin A.5.2(58)
Float 3.5.7(12), see 3.5.7(14), see A.1(12), see 3.5.7(14), see A.1(21).
Float_Random
child of Ada.Numerics A.5.2.
Float_Text_IO
child of Ada A.10.9.
Float_Type A.5.1.
Float_Wide_Text_IO
child of Ada A.11.
Float_IO A.10.1.
Floating B.4.
floating point type 3.5.7.
floating_point_definition 3.5.7.
used 3.5.6(2), see P(2), see P(1).
Floor attribute A.5.3(30), see K(30), see K(74).
Flush A.10.1(21), see A.12.1(21), see A.12.1(25).
Fore attribute 3.5.10(4), see K(4), see K(78).
form A.8.1(9), see A.8.4(9), see A.10.1(9), see A.8.4(9), see A.10.1(12),
A.12.1.
of an external file A.7.
formal object, generic 12.4.
formal package, generic 12.7.
formal parameter
of a subprogram 6.1.
formal subprogram, generic 12.6.
formal subtype 12.5.
formal type 12.5.
formal_access_type_definition 12.5.4.
used 12.5(3), see P(3), see P(1).
formal_array_type_definition 12.5.3.
used 12.5(3), see P(3), see P(1).
formal_decimal_fixed_point_definition 12.5.2.
used 12.5(3), see P(3), see P(1).
formal_derived_type_definition 12.5.1.
used 12.5(3), see P(3), see P(1).
formal_discrete_type_definition 12.5.2.
used 12.5(3), see P(3), see P(1).
formal_floating_point_definition 12.5.2.
used 12.5(3), see P(3), see P(1).
formal_modular_type_definition 12.5.2.
used 12.5(3), see P(3), see P(1).
formal_object_declaration 12.4.
used 12.1(6), see P(6), see P(1).
formal_ordinary_fixed_point_definition 12.5.2.
used 12.5(3), see P(3), see P(1).
formal_package_actual_part 12.7.
used 12.7(2), see P(2), see P(1).
formal_package_declaration 12.7.
used 12.1(6), see P(6), see P(1).
formal_part 6.1.
used 6.1(12), see 6.1(13), see P(12), see 6.1(13), see P(1).
formal_private_type_definition 12.5.1.
used 12.5(3), see P(3), see P(1).
formal_signed_integer_type_definition 12.5.2.
used 12.5(3), see P(3), see P(1).
formal_subprogram_declaration 12.6.
used 12.1(6), see P(6), see P(1).
formal_type_declaration 12.5.
used 12.1(6), see P(6), see P(1).
formal_type_definition 12.5.
used 12.5(2), see P(2), see P(1).
format_effector 2.1.
used 2.1(2), see P(2), see P(1).
Fortran
child of Interfaces B.5.
Fortran interface B.5.
FORTRAN standard 1.2.
Fortran_Character B.5.
Fortran_Integer B.5.
Fortran_Library B.1.
Fortran_Matrix B.5.
Fraction 3.5.9.
Fraction attribute A.5.3(21), see K(21), see K(80).
Fraction_One_Half A.3.3.
Fraction_One_Quarter A.3.3.
Fraction_Three_Quarters A.3.3.
Free 13.11.2(5), see A.4.5(7), see B.3.1(5), see A.4.5(7), see B.3.1(11).
freed
See nonexistent 13.11.2.
freeing storage 13.11.2.
freezing
by a constituent of a construct 13.14.
by an expression 13.14.
class-wide type caused by the freezing of the specific type
13.14.
constituents of a full type definition 13.14.
designated subtype caused by an allocator 13.14.
entity 13.14.
entity caused by a body 13.14.
entity caused by a construct 13.14.
entity caused by a name 13.14.
entity caused by the end of an enclosing construct
13.14.
first subtype caused by the freezing of the type
13.14.
function call 13.14.
generic_instantiation 13.14.
nominal subtype caused by a name 13.14.
object_declaration 13.14.
specific type caused by the freezing of the class-wide type
13.14.
subtype caused by a record extension 13.14.
subtypes of the profile of a callable entity 13.14.
type caused by a range 13.14.
type caused by an expression 13.14.
type caused by the freezing of a subtype 13.14.
freezing points
entity 13.14.
FS A.3.3(6), see J.5(6), see J.5(4).
full conformance
for discrete_subtype_definitions 6.3.1.
for known_discriminant_parts 6.3.1.
for expressions 6.3.1.
for profiles 6.3.1.
required 3.10.1(4), see 6.3(4), 7.3(4), see 6.3(4), 7.3(9),
8.5.4(5), 9.5.2(14), 9.5.2(5), 9.5.2(14), 9.5.2(16),
9.5.2(17), see 10.1.3(11), see 10.1.3(17), see 10.1.3(11), see 10.1.3(12).
full constant declaration 3.3.1.
full declaration 7.4.
full stop 2.1.
full type 3.2.1.
full type definition 3.2.1.
full view
of a type 7.3.
Full_Stop A.3.3.
full_type_declaration 3.2.1.
used 3.2.1(2), see P(2), see P(1).
function 6.
function instance 12.3.
function_call 6.4.
used 4.1(2), see P(2), see P(1).
ΓòÉΓòÉΓòÉ 37. index ΓòÉΓòÉΓòÉ
gaps 13.1.
garbage collection 13.11.3.
Gender 3.5.1.
general access type 3.10(7), see 3.10(7), see 3.10(8).
general_access_modifier 3.10.
used 3.10(3), see P(3), see P(1).
generation
of an interrupt C.3.
Generator A.5.2(7), see A.5.2(7), see A.5.2(19).
generic actual 12.3.
generic actual parameter 12.3.
generic actual subtype 12.5.
generic actual type 12.5.
generic body 12.2.
generic contract issue 10.2.1.
[partial] 3.9.1(3), 3.10.2(3), 3.10.2(28),
3.10.2(32), see 4.6(32), see 4.6(17),
4.6(20), 8.3(20), 8.3(26),
10.2.1.
generic formal 12.1.
generic formal object 12.4.
generic formal package 12.7.
generic formal subprogram 12.6.
generic formal subtype 12.5.
generic formal type 12.5.
generic function 12.1.
generic package 12.1.
generic procedure 12.1.
generic subprogram 12.1.
generic unit 12(1), see N(1), see N(20).
See also dispatching operation 3.9.
generic_actual_part 12.3.
used 12.3(2), see 12.7(3), see P(2), see 12.7(3), see P(1).
generic_association 12.3.
used 12.3(3), see P(3), see P(1).
Generic_Bounded_Length A.4.4.
Generic_Complex_Elementary_Functions
child of Ada.Numerics G.1.2.
Generic_Complex_Types
child of Ada.Numerics G.1.1.
generic_declaration 12.1.
used 3.1(3), see 10.1.1(5), see P(3), see 10.1.1(5), see P(1).
Generic_Elementary_Functions
child of Ada.Numerics A.5.1.
generic_formal_parameter_declaration 12.1.
used 12.1(5), see P(5), see P(1).
generic_formal_part 12.1.
used 12.1(3), see 12.1(4), see P(3), see 12.1(4), see P(1).
generic_instantiation 12.3.
used 3.1(3), see 10.1.1(5), see P(3), see 10.1.1(5), see P(1).
generic_package_declaration 12.1.
used 12.1(2), see P(2), see P(1).
generic_renaming_declaration 8.5.5.
used 8.5(2), see 10.1.1(6), see P(2), see 10.1.1(6), see P(1).
generic_subprogram_declaration 12.1.
used 12.1(2), see P(2), see P(1).
Get 10.1.1(30), see A.10.1(41), see A.10.1(30), see A.10.1(41), see A.10.1(47),
A.10.1(54), see A.10.1(55), see A.10.1(54), see A.10.1(55), see A.10.1(59),
A.10.1(60), see A.10.1(65), see A.10.1(60), see A.10.1(65), see A.10.1(67),
A.10.1(70), see A.10.1(72), see A.10.1(70), see A.10.1(72), see A.10.1(75),
A.10.1(77), see A.10.1(81), see A.10.1(77), see A.10.1(81), see A.10.1(83),
G.1.3(6), G.1.3(6), G.1.3(8).
Get_Immediate A.10.1(44), see A.10.1(44), see A.10.1(45).
Get_Key 7.3.1(15), see 7.3.1(15), see 7.3.1(16).
Get_Line A.10.1.
Get_Priority D.5.
Global 9.3.
global to 8.1.
Glossary N.
goto_statement 5.8.
used 5.1(4), see P(4), see P(1).
govern a variant_part 3.8.1.
govern a variant 3.8.1.
grammar
complete listing P.
cross reference P.
notation 1.1.4.
resolution of ambiguity 8.6.
under Syntax heading 1.1.2.
graphic character
a category of Character A.3.2.
graphic_character 2.1.
used 2.1(2), see 2.5(2), see 2.6(3), see P(2), see 2.5(2), see 2.6(3), see P(1).
Graphic_Set A.4.6.
greater than operator 4.4(1), see 4.5.2(1), see 4.5.2(1).
greater than or equal operator 4.4(1), see 4.5.2(1), see 4.5.2(1).
greater-than sign 2.1.
Greater_Than_Sign A.3.3.
GS A.3.3.
guard 9.7.1.
used 9.7.1(2), see P(2), see P(1).
ΓòÉΓòÉΓòÉ 38. index ΓòÉΓòÉΓòÉ
Half_Pi 4.9.
handle
an exception 11(1), see N(1), see N(18).
an exception occurrence 11.4(1), see 11.4(1), see 11.4(7).
handled_sequence_of_statements 11.2.
used 5.6(2), see 6.3(2), 7.2(2), see 6.3(2), 7.2(2),
9.1(6), see 9.5.2(3), see 9.5.2(6), see 9.5.2(3), see 9.5.2(5),
P.
Handler C.3.2.
Handling
child of Ada.Characters A.3.2.
Hash_Index 3.5.4.
head (of a queue) D.2.1.
Head A.4.3(35), see A.4.3(36), see A.4.4(35), see A.4.3(36), see A.4.4(70),
A.4.4(71), see A.4.5(65), see A.4.5(71), see A.4.5(65), see A.4.5(66).
heap management
See also alligator 4.8.
user-defined 13.11.
held priority D.11.
Hello 3.3.1.
heterogeneous input-output A.12.1.
Hexa 3.5.1.
hexadecimal
literal 2.4.2.
hexadecimal digit
a category of Character A.3.2.
hexadecimal literal 2.4.2.
Hexadecimal_Digit_Set A.4.6.
hidden from all visibility 8.3(5), see 8.3(5), see 8.3(14).
by lack of a with_clause 8.3.
for a declaration completed by a subsequent declaration
8.3.
for overridden declaration 8.3.
within the declaration itself 8.3.
hidden from direct visibility 8.3(5), see 8.3(5), see 8.3(21).
by an inner homograph 8.3.
where hidden from all visibility 8.3.
hiding 8.3.
High_Order_First 13.5.3(2), see B.4(2), see B.4(25).
highest precedence operator 4.5.6.
highest_precedence_operator 4.5.
Hold D.11.
homograph 8.3.
HT A.3.3.
HTJ A.3.3.
HTS A.3.3.
Hyphen A.3.3.
hyphen-minus 2.1.
ΓòÉΓòÉΓòÉ 39. index ΓòÉΓòÉΓòÉ
i G.1.1(5), see G.1.1(5), see G.1.1(23).
identifier 2.3.
used 2.8(2), 2.8(3), 2.8(2), 2.8(3), 2.8(21),
2.8(23), 3.1(4), 4.1(23), 3.1(4), 4.1(3),
4.1.3(3), see 4.1.4(3), see 5.5(3), see 4.1.4(3), see 5.5(2),
5.6(2), 6.1(5), 7.1(2), 6.1(5), 7.1(3),
7.2(2), 9.1(4), 9.1(2), 9.1(4), 9.1(6),
9.4(4), 9.4(7), 9.5.2(4), 9.4(7), 9.5.2(3),
9.5.2(5), see 11.5(4), 13.12(5), see 11.5(4), 13.12(4),
B.1(5), B.1(6), B.1(5), B.1(6), B.1(7),
D.2.2(2), see D.2.2(3), see D.3(2), see D.2.2(3), see D.3(3),
D.3(4), D.4(3), D.4(4), D.4(3), D.4(4),
L(8), L(13), L(8), L(13), L(14),
L(20), L(21), L(20), L(21), L(23),
L(29), L(36), L(29), L(36), L(37),
M(95), M(98), P(95), M(98), P(1).
identifier specific to a pragma 2.8.
identifier_letter 2.1.
used 2.1(3), see 2.3(2), see 2.3(3), see P(3), see 2.3(2), see 2.3(3), see P(1).
Identity A.4.2(22), see A.4.7(22), see A.4.7(22).
Identity attribute 11.4.1(9), see C.7.1(9), see C.7.1(12),
K(84), K(84), K(86).
idle task D.11.
if_statement 5.3.
used 5.1(5), see P(5), see P(1).
illegal
construct 1.1.2.
partition 1.1.2.
Im G.1.1.
image A.5.2(14), see A.5.2(26), see C.7.1(14), see A.5.2(26), see C.7.1(3),
F.3.3.
of a value 3.5(30), see K(30), see K(273).
Image attribute 3.5(35), see K(35), see K(88).
Imaginary B.5(10), see G.1.1(4), see G.1.1(10), see G.1.1(4), see G.1.1(23).
immediate scope
of (a view of) an entity 8.2.
of a declaration 8.2.
immediately enclosing 8.1.
immediately visible 8.3(4), see 8.3(4), see 8.3(21).
immediately within 8.1(13)
implementation advice 1.1.2.
implementation defined 1.1.3.
summary of characteristics M.
implementation permissions 1.1.2.
implementation requirements 1.1.2.
implementation-dependent
See unspecified 1.1.3.
implicit declaration 3.1(5), see N(5), see N(11).
implicit initial values
for a subtype 3.3.1.
implicit subtype conversion 4.6(59), see 4.6(59), see 4.6(60).
Access attribute 3.10.2.
access discriminant 3.7.
array bounds 4.6.
array index 4.1.1.
assignment to view conversion 4.6.
assignment_statement 5.2.
bounds of a decimal fixed point type 3.5.9.
bounds of a fixed point type 3.5.9.
bounds of a floating point type 3.5.7.
bounds of a range 3.5(9), see 3.6(9), see 3.6(18).
bounds of signed integer type 3.5.4.
choices of aggregate 4.3.3.
component defaults 3.3.1.
delay expression 9.6.
derived type discriminants 3.4.
discriminant values 3.7.1.
entry index 9.5.2.
expressions in aggregate 4.3.1.
expressions of aggregate 4.3.3.
function return 6.5.
generic formal object of mode in 12.4(11)
inherited enumeration literal 3.4.
initialization expression 3.3.1.
initialization expression of allocator 4.8.
named number value 3.3.2.
operand of concatenation 4.5.3.
parameter passing 6.4.1(10), see 6.4.1(10), see 6.4.1(11),
6.4.1.
pragma Interrupt_Priority D.1(17), see D.3(17), see D.3(9).
pragma Priority D.1(17), see D.3(17), see D.3(9).
qualified_expression 4.7.
reading a view conversion 4.6.
result of inherited function 3.4.
implicit_dereference 4.1.
used 4.1(4), see P(4), see P(1).
Import pragma B.1(5), see L(5), see L(14).
imported
aspect of representation B.1.
imported entity B.1.
in (membership test) 4.4(1), see 4.5.2(1), see 4.5.2(2).
inaccessible partition E.1.
inactive
a task state 9.
included
one range in another 3.5.
incomplete type 3.10.1.
incomplete_type_declaration 3.10.1.
used 3.2.1(2), see P(2), see P(1).
Increment 6.1(37), see B.3.2(37), see B.3.2(11).
indefinite subtype 3.3(23), see 3.7(23), see 3.7(26).
independent subprogram 11.6.
independently addressable 9.10.
Index 12.1(19), 12.5.3(11), see A.4.3(19), 12.5.3(11), see A.4.3(9),
A.4.3(10), see A.4.3(11), A.4.4(10), see A.4.3(11), A.4.4(44),
A.4.4(45), see A.4.4(46), A.4.5(45), see A.4.4(46), A.4.5(39),
A.4.5(40), see A.4.5(41), A.8.4(40), see A.4.5(41), A.8.4(15),
A.12.1(23), see B.3.2(23), see B.3.2(4).
of an element of an open direct file A.8.
index range 3.6.
index subtype 3.6.
index type 3.6.
Index_Check 11.5.
[partial] 4.1.1(7), 4.1.2(7), see 4.3.3(7), 4.1.2(7), see 4.3.3(29),
4.3.3(30), see 4.5.3(8), see 4.6(30), see 4.5.3(8), see 4.6(51),
4.7(4), 4.8(4), 4.8(10).
index_constraint 3.6.1.
used 3.2.2(7), see P(7), see P(1).
Index_Non_Blank A.4.3(12), see A.4.4(12), see A.4.4(47),
A.4.5.
index_subtype_definition 3.6.
used 3.6(3), see P(3), see P(1).
indexed_component 4.1.1.
used 4.1(2), see P(2), see P(1).
indivisible C.6.
information hiding
See package 7.
See private types and private extensions 7.3.
information systems C(1), see F(1), see F(1).
informative 1.1.2.
inheritance
See also tagged types and type extension 3.9.
See derived types and classes 3.4.
inherited
from an ancestor type 3.4.1.
inherited component 3.4(11), see 3.4(11), see 3.4(12).
inherited discriminant 3.4.
inherited entry 3.4.
inherited protected subprogram 3.4.
inherited subprogram 3.4.
initialization
of a protected object 9.4(14), see C.3.1(14), see C.3.1(10),
C.3.1.
of a task object 9.1(12), see J.7.1(12), see J.7.1(7).
of an object 3.3.1.
initialization expression 3.3.1(1), see 3.3.1(1), see 3.3.1(4).
Initialize 7.6(2), see 7.6(6), see 7.6(2), see 7.6(6), see 7.6(8).
Initialize_Generator A.5.2.
initialized allocator 4.8.
Inline pragma 6.3.2(3), see L(3), see L(15).
Inner 10.1.3(20), see 10.1.3(21), see 10.1.3(20), see 10.1.3(21), see 10.1.3(23),
10.1.3.
innermost dynamically enclosing 11.4.
input A.6.
Input attribute 13.13.2(22), see 13.13.2(22), see 13.13.2(32),
K(92), K(92), K(96).
Input clause 13.3(7), see 13.13.2(7), see 13.13.2(36).
input-output
unspecified for access types A.7.
Insert A.4.3(25), see A.4.3(26), see A.4.4(25), see A.4.3(26), see A.4.4(60),
A.4.4(61), see A.4.5(55), see A.4.5(61), see A.4.5(55), see A.4.5(56).
inspectable object H.3.2.
inspection point H.3.2.
Inspection_Point pragma H.3.2(3), see L(3), see L(16).
instance
of a generic function 12.3.
of a generic package 12.3.
of a generic procedure 12.3.
of a generic subprogram 12.3.
of a generic unit 12.3.
instructions for comment submission
Int 3.2.2(15), see 12.5(13), see B.3(15), see 12.5(13), see B.3(7).
Int_Plus 8.5.4.
Int_Vectors 12.3.
Int_IO A.10.8.
Integer 3.5.4(11), see 3.5.4(21), see A.1(11), see 3.5.4(21), see A.1(12).
integer literal 2.4.
integer literals 3.5.4(14), see 3.5.4(14), see 3.5.4(30).
integer type 3.5.4(1), see N(1), see N(21).
Integer_Address 13.7.1.
Integer_Text_IO
child of Ada A.10.8.
integer_type_definition 3.5.4.
used 3.2.1(4), see P(4), see P(1).
Integer_Wide_Text_IO
child of Ada A.11.
Integer_IO A.10.1.
interaction
between tasks 9.
interface to assembly language C.1.
interface to C B.3.
interface to COBOL B.4.
interface to Fortran B.5.
interface to other languages B.
Interfaces B.2.
Interfaces.COBOL B.4.
Interfaces.Fortran B.5.
Interfaces.C B.3.
Interfaces.C.Pointers B.3.2.
Interfaces.C.Strings B.3.1.
interfacing pragma B.1.
Convention B.1.
Export B.1.
Import B.1.
internal call 9.5.
internal code 13.4.
internal requeue 9.5.
Internal_Tag 3.9.
interpretation
of a complete context 8.6.
of a constituent of a complete context 8.6.
overload resolution 8.6.
interrupt C.3.
example using asynchronous_select 9.7.4,
9.7.4.
interrupt entry J.7.1.
interrupt handler C.3.
Interrupt_Handler J.7.1.
Interrupt_Handler pragma C.3.1(2), see L(2), see L(17).
Interrupt_Priority 13.7(16), see D.1(16), see D.1(10).
Interrupt_Priority pragma D.1(5), see L(5), see L(18).
Interrupt_ID C.3.2.
Interrupts
child of Ada C.3.2.
Intersection 3.9.3.
intertask communication 9.5.
See also task 9.
Intrinsic calling convention 6.3.1.
invalid representation 13.9.1.
Invert B.5.
Inverted_Exclamation A.3.3.
Inverted_Question A.3.3.
IO_Exceptions J.1.
child of Ada A.13.
IO_Package 7.5(18), see 7.5(18), see 7.5(20).
Is_Alphanumeric A.3.2.
Is_Attached C.3.2.
Is_Basic A.3.2.
Is_Callable C.7.1.
Is_Character A.3.2.
Is_Control A.3.2.
Is_Decimal_Digit A.3.2.
Is_Digit A.3.2.
Is_Graphic A.3.2.
Is_Held D.11.
Is_Hexadecimal_Digit A.3.2.
Is_ISO_646 A.3.2.
Is_Letter A.3.2.
Is_Lower A.3.2.
Is_Open A.8.1(10), see A.8.4(10), see A.10.1(10), see A.8.4(10), see A.10.1(13),
A.12.1.
Is_Reserved C.3.2.
Is_Special A.3.2.
Is_String A.3.2.
Is_Subset A.4.2(14), see A.4.7(14), see A.4.7(14).
Is_Terminated C.7.1.
Is_Upper A.3.2.
Is_In A.4.2(13), see A.4.7(13), see A.4.7(13).
ISO 10646 3.5.2(2), see 3.5.2(2), see 3.5.2(3).
ISO 1989:1985 1.2.
ISO/IEC 10646-1:1993 1.2.
ISO/IEC 1539:1991 1.2.
ISO/IEC 6429:1992 1.2.
ISO/IEC 646:1991 1.2.
ISO/IEC 8859-1:1987 1.2.
ISO/IEC 9899:1990 1.2.
ISO_646 A.3.2.
ISO_646_Set A.4.6.
issue
an entry call 9.5.3.
italics
nongraphic characters 3.5.2.
pseudo-names of anonymous types 3.2.1(7), see A.1(7), see A.1(2).
syntax rules 1.1.4.
terms introduced or defined 1.3.
Item 3.7(37), 12.1(19), see 12.1(37), 12.1(19), see 12.1(22),
12.1(24), see 12.5(12), see 12.5.3(24), see 12.5(12), see 12.5.3(11),
12.8(3), 12.8(3), 12.8(14).
Iterate 12.6.
iteration_scheme 5.5.
used 5.5(2), see P(2), see P(1).
ΓòÉΓòÉΓòÉ 40. index ΓòÉΓòÉΓòÉ
j G.1.1(5), see G.1.1(5), see G.1.1(23).
ΓòÉΓòÉΓòÉ 41. index ΓòÉΓòÉΓòÉ
Key 7.3(22), see 7.3.1(22), see 7.3.1(15).
Key_Manager 7.3.1(15), see 7.3.1(15), see 7.3.1(16).
Keyboard 9.1.
Keyboard_Driver 9.1.
Kilo 4.9.
known discriminants 3.7.
known_discriminant_part 3.7.
used 3.2.1(3), see 3.7(2), see 9.1(3), see 3.7(2), see 9.1(2),
9.4(2), P(2), P(1).
ΓòÉΓòÉΓòÉ 42. index ΓòÉΓòÉΓòÉ
L_Brace J.5.
L_Bracket J.5.
label 5.1.
used 5.1(3), see P(3), see P(1).
language
interface to assembly C.1.
interface to non-Ada B.
language-defined check 11.5(2), see 11.6(2), see 11.6(1).
language-defined class
[partial] 3.2.
of types 3.2.
Language-Defined Library Units A.
Ada A.2.
Ada.Asynchronous_Task_Control D.11.
Ada.Calendar 9.6.
Ada.Characters A.3.1.
Ada.Characters.Handling A.3.2.
Ada.Characters.Latin_1 A.3.3.
Ada.Command_Line A.15.
Ada.Decimal F.2.
Ada.Direct_IO A.8.4(2), see A.9(2), see A.9(3).
Ada.Dynamic_Priorities D.5.
Ada.Exceptions 11.4.1.
Ada.Finalization 7.6.
Ada.Float_Text_IO A.10.9.
Ada.Float_Wide_Text_IO A.11.
Ada.Integer_Text_IO A.10.8.
Ada.Integer_Wide_Text_IO A.11.
Ada.Interrupts C.3.2.
Ada.Interrupts.Names C.3.2.
Ada.IO_Exceptions A.13.
Ada.Numerics A.5.
Ada.Numerics.Complex_Elementary_Functions G.1.2.
Ada.Numerics.Complex_Types G.1.1.
Ada.Numerics.Discrete_Random A.5.2.
Ada.Numerics.Elementary_Functions A.5.1.
Ada.Numerics.Float_Random A.5.2.
Ada.Numerics.Generic_Complex_Elementary_Functions
G.1.2.
Ada.Numerics.Generic_Complex_Types G.1.1.
Ada.Numerics.Generic_Elementary_Functions A.5.1.
Ada.Real_Time D.8.
Ada.Sequential_IO A.8.1.
Ada.Storage_IO A.9.
Ada.Streams 13.13.1.
Ada.Streams.Stream_IO A.12.1.
Ada.Strings A.4.1.
Ada.Strings.Bounded A.4.4.
Ada.Strings.Fixed A.4.3.
Ada.Strings.Maps A.4.2.
Ada.Strings.Maps.Constants A.4.6.
Ada.Strings.Unbounded A.4.5.
Ada.Strings.Wide_Bounded A.4.7.
Ada.Strings.Wide_Fixed A.4.7.
Ada.Strings.Wide_Maps A.4.7.
Ada.Strings.Wide_Maps.Wide_Constants A.4.7.
Ada.Strings.Wide_Unbounded A.4.7.
Ada.Synchronous_Task_Control D.10.
Ada.Tags 3.9.
Ada.Task_Attributes C.7.2.
Ada.Task_Identification C.7.1.
Ada.Text_IO A.10.1.
Ada.Text_IO.Complex_IO G.1.3.
Ada.Text_IO.Editing F.3.3.
Ada.Text_IO.Text_Streams A.12.2.
Ada.Unchecked_Conversion 13.9.
Ada.Unchecked_Deallocation 13.11.2.
Ada.Wide_Text_IO A.11.
Ada.Wide_Text_IO.Complex_IO G.1.4.
Ada.Wide_Text_IO.Editing F.3.4.
Ada.Wide_Text_IO.Text_Streams A.12.3.
Interfaces B.2.
Interfaces.C B.3.
Interfaces.C.Pointers B.3.2.
Interfaces.C.Strings B.3.1.
Interfaces.COBOL B.4.
Interfaces.Fortran B.5.
Standard A.1.
System 13.7.
System.Address_To_Access_Conversions 13.7.2.
System.Machine_Code 13.8.
System.RPC E.5.
System.Storage_Elements 13.7.1.
System.Storage_Pools 13.11.
Language-Defined Types
Address, in System 13.7.
Alignment, in Ada.Strings A.4.1.
Alphanumeric, in Interfaces.COBOL B.4.
Attribute_Handle, in Ada.Task_Attributes C.7.2.
Binary, in Interfaces.COBOL B.4.
Binary_Format, in Interfaces.COBOL B.4.
Bit_Order, in System 13.7.
Boolean, in Standard A.1.
Bounded_String, in Ada.Strings.Bounded.Generic_Bounded_Length
A.4.4.
Byte, in Interfaces.COBOL B.4.
Byte_Array, in Interfaces.COBOL B.4.
C_float, in Interfaces.C B.3.
char, in Interfaces.C B.3.
char_array, in Interfaces.C B.3.
char_array_access, in Interfaces.C B.3.1.
Character, in Standard A.1.
Character_Set, in Ada.Strings.Maps A.4.2.
chars_ptr, in Interfaces.C B.3.1.
chars_ptr_array, in Interfaces.C B.3.1.
COBOL_Character, in Interfaces.COBOL B.4.
Complex, in Ada.Numerics.Generic_Complex_Types G.1.1.
Controlled, in Ada.Finalization 7.6.
Count, in Ada.Direct_IO A.8.4.
Count, in Ada.Text_IO A.10.1.
Decimal_Element, in Interfaces.COBOL B.4.
Direction, in Ada.Strings A.4.1.
Display_Format, in Interfaces.COBOL B.4.
double, in Interfaces.C B.3.
Duration, in Standard A.1.
Exception_Occurrence, in Ada.Exceptions 11.4.1.
Exception_Occurrence_Access, in Ada.Exceptions 11.4.1.
Exception_Id, in Ada.Exceptions 11.4.1.
File_Mode, in Ada.Direct_IO A.8.4.
File_Mode, in Ada.Sequential_IO A.8.1.
File_Mode, in Ada.Text_IO A.10.1.
File_Type, in Ada.Direct_IO A.8.4.
File_Type, in Ada.Sequential_IO A.8.1.
File_Type, in Ada.Text_IO A.10.1.
Float, in Standard A.1.
Floating, in Interfaces.COBOL B.4.
Generator, in Ada.Numerics.Discrete_Random A.5.2.
Generator, in Ada.Numerics.Float_Random A.5.2.
Imaginary, in Ada.Numerics.Generic_Complex_Types G.1.1.
int, in Interfaces.C B.3.
Integer, in Standard A.1.
Integer_Address, in System.Storage_Elements 13.7.1.
Interrupt_ID, in Ada.Interrupts C.3.2.
Limited_Controlled, in Ada.Finalization 7.6.
long, in Interfaces.C B.3.
Long_Binary, in Interfaces.COBOL B.4.
long_double, in Interfaces.C B.3.
Long_Floating, in Interfaces.COBOL B.4.
Membership, in Ada.Strings A.4.1.
Name, in System 13.7.
Numeric, in Interfaces.COBOL B.4.
Packed_Decimal, in Interfaces.COBOL B.4.
Packed_Format, in Interfaces.COBOL B.4.
Parameterless_Handler, in Ada.Interrupts C.3.2.
Partition_ID, in System.RPC E.5.
Picture, in Ada.Text_IO.Editing F.3.3.
Picture, in Ada.Wide_Text_IO.Editing F.3.4.
plain_char, in Interfaces.C B.3.
Pointer, in Interfaces.C.Pointers B.3.2.
ptrdiff_t, in Interfaces.C B.3.
Root_Storage_Pool, in System.Storage_Pools 13.11.
Root_Stream_Type, in Ada.Streams 13.13.1.
Seconds_Count, in Ada.Real_Time D.8.
short, in Interfaces.C B.3.
signed_char, in Interfaces.C B.3.
size_t, in Interfaces.C B.3.
State, in Ada.Numerics.Discrete_Random A.5.2.
State, in Ada.Numerics.Float_Random A.5.2.
Storage_Array, in System.Storage_Elements 13.7.1.
Storage_Element, in System.Storage_Elements 13.7.1.
Storage_Offset, in System.Storage_Elements 13.7.1.
Stream_Access, in Ada.Streams.Stream_IO A.12.1.
String, in Standard A.1.
Suspension_Object, in Ada.Synchronous_Task_Control
D.10.
Tag, in Tags 3.9.
Task_ID, in Ada.Task_Identification C.7.1.
Time, in Ada.Calendar 9.6.
Time, in Ada.Real_Time D.8.
Time_Span, in Ada.Real_Time D.8.
Trim_End, in Ada.Strings A.4.1.
Truncation, in Ada.Strings A.4.1.
Type_Set, in Ada.Text_IO A.10.1.
Unbounded_String, in Ada.Strings.Unbounded A.4.5.
unsigned, in Interfaces.C B.3.
unsigned_char, in Interfaces.C B.3.
unsigned_long, in Interfaces.C B.3.
unsigned_short, in Interfaces.C B.3.
wchar_array, in Interfaces.C B.3.
wchar_t, in Interfaces.C B.3.
Wide_Character, in Standard A.1.
Wide_Character_Set, in Ada.Strings.Wide_Maps A.4.7.
Wide_String, in Standard A.1.
Last attribute 3.5(13), see 3.6.2(5), see K(13), see 3.6.2(5), see K(102),
K.
Last(N) attribute 3.6.2(6), see K(6), see K(100).
last_bit 13.5.1.
used 13.5.1(3), see P(3), see P(1).
Last_Bit attribute 13.5.2(4), see K(4), see K(106).
lateness D.9.
Latin-1 3.5.2.
Latin_1
child of Ada.Characters A.3.3.
layout
aspect of representation 13.5.
Layout_Error A.10.1(85), see A.13(85), see A.13(4).
LC_German_Sharp_S A.3.3.
LC_Icelandic_Eth A.3.3.
LC_Icelandic_Thorn A.3.3.
LC_A A.3.3(13), see J.5(13), see J.5(8).
LC_A_Acute A.3.3.
LC_A_Circumflex A.3.3.
LC_A_Diaeresis A.3.3.
LC_A_Grave A.3.3.
LC_A_Ring A.3.3.
LC_A_Tilde A.3.3.
LC_AE_Diphthong A.3.3.
LC_B A.3.3.
LC_C A.3.3.
LC_C_Cedilla A.3.3.
LC_D A.3.3.
LC_E A.3.3.
LC_E_Acute A.3.3.
LC_E_Circumflex A.3.3.
LC_E_Diaeresis A.3.3.
LC_E_Grave A.3.3.
LC_F A.3.3.
LC_G A.3.3.
LC_H A.3.3.
LC_I A.3.3.
LC_I_Acute A.3.3.
LC_I_Circumflex A.3.3.
LC_I_Diaeresis A.3.3.
LC_I_Grave A.3.3.
LC_J A.3.3.
LC_K A.3.3.
LC_L A.3.3.
LC_M A.3.3.
LC_N A.3.3.
LC_N_Tilde A.3.3.
LC_O A.3.3.
LC_O_Acute A.3.3.
LC_O_Circumflex A.3.3.
LC_O_Diaeresis A.3.3.
LC_O_Grave A.3.3.
LC_O_Oblique_Stroke A.3.3.
LC_O_Tilde A.3.3.
LC_P A.3.3.
LC_Q A.3.3.
LC_R A.3.3.
LC_S A.3.3.
LC_T A.3.3.
LC_U A.3.3.
LC_U_Acute A.3.3.
LC_U_Circumflex A.3.3.
LC_U_Diaeresis A.3.3.
LC_U_Grave A.3.3.
LC_V A.3.3.
LC_W A.3.3.
LC_X A.3.3.
LC_Y A.3.3.
LC_Y_Acute A.3.3.
LC_Y_Diaeresis A.3.3.
LC_Z A.3.3(14), see J.5(14), see J.5(8).
Leading_Nonseparate B.4.
Leading_Part attribute A.5.3(54), see K(54), see K(108).
Leading_Separate B.4.
leaving 7.6.1.
left 7.6.1.
left curly bracket 2.1.
left parenthesis 2.1.
left square bracket 2.1.
Left_Angle_Quotation A.3.3.
Left_Curly_Bracket A.3.3.
Left_Parenthesis A.3.3.
Left_Square_Bracket A.3.3.
legal
construct 1.1.2.
partition 1.1.2.
legality rules 1.1.2.
length A.4.4(9), see A.4.5(6), see B.4(9), see A.4.5(6), see B.4(34),
B.4(39), B.4(44), F.3.3(39), B.4(44), F.3.3(11).
of a dimension of an array 3.6.
of a one-dimensional array 3.6.
Length attribute 3.6.2(9), see K(9), see K(117).
Length(N) attribute 3.6.2(10), see K(10), see K(115).
Length_Check 11.5.
[partial] 4.5.1(8), see 4.6(37), see 4.6(8), see 4.6(37), see 4.6(52).
Length_Error 12.1.
Length_Range A.4.4.
less than operator 4.4(1), see 4.5.2(1), see 4.5.2(1).
less than or equal operator 4.4(1), see 4.5.2(1), see 4.5.2(1).
less-than sign 2.1.
Less_Than_Sign A.3.3.
letter
a category of Character A.3.2.
Letter_Set A.4.6.
letter_or_digit 2.3.
used 2.3(2), see P(2), see P(1).
Level 3.5.1.
accessibility 3.10.2.
library 3.10.2.
lexical element 2.2.
lexicographic order 4.5.2.
LF A.3.3(5), see J.5(5), see J.5(4).
library 10.1.4.
informal introduction 10.
library level 3.10.2.
library unit 10.1(3), see 10.1.1(9), see N(3), see 10.1.1(9), see N(22).
informal introduction 10.
See also language-defined library units
library unit pragma 10.1.5.
All_Calls_Remote E.2.3.
categorization pragmas E.2.
Elaborate_Body 10.2.1.
Preelaborate 10.2.1.
Pure 10.2.1.
library_item 10.1.1.
used 10.1.1(3), see P(3), see P(1).
informal introduction 10.
library_unit_body 10.1.1.
used 10.1.1(4), see P(4), see P(1).
library_unit_declaration 10.1.1.
used 10.1.1(4), see P(4), see P(1).
library_unit_renaming_declaration 10.1.1.
used 10.1.1(4), see P(4), see P(1).
lifetime 3.10.2.
Light 3.5.1.
Limit 3.3.1(33), see 7.5(33), see 7.5(20).
limited type 7.5(1), see 7.5(3), see N(1), see 7.5(3), see N(23).
becoming nonlimited 7.3.1(5), see 7.5(5), see 7.5(16).
Limited_Controlled 7.6.
line 2.2(2), see 3.6(28), see A.10.1(2), see 3.6(28), see A.10.1(38).
line terminator A.10.
Line_Length A.10.1.
Line_Size 3.5.4.
Link 3.10.1(15), see 12.5.4(15), see 12.5.4(8).
link name B.1.
link-time error
See post-compilation error 1.1.2(29), see 1.1.5(29), see 1.1.5(4).
Linker_Options pragma B.1(8), see L(8), see L(19).
linking
See partition building 10.2.
List 7.3.
List pragma 2.8(21), see L(21), see L(20).
literal 3.9.1(13), see 4.2(13), see 4.2(1).
See also aggregate 4.3.
based 2.4.2.
decimal 2.4.1.
numeric 2.4.
little endian 13.5.3.
load time C.4.
Local 9.3.
local to 8.1.
Local_Coordinate 3.4.
local_name 13.1.
used 13.2(3), 13.3(2), 13.4(3), 13.3(2), 13.4(2),
13.5.1(2), see 13.5.1(3), see 13.11.3(2), see 13.5.1(3), see 13.11.3(3),
B.1(5), B.1(6), B.1(5), B.1(6), B.1(7),
C.5(3), C.6(3), C.6(3), C.6(3), C.6(4),
C.6(5), C.6(6), E.4.1(5), C.6(6), E.4.1(3),
L(3), L(4), L(3), L(4), L(5),
L(7), L(8), L(7), L(8), L(9),
L(13), L(14), L(13), L(14), L(24),
L(38), L(39), P(38), L(39), P(1).
localization 3.5.2(4), see 3.5.2(4), see 3.5.2(5).
Lock D.12(9), see D.12(9), see D.12(10).
locking policy D.3.
Locking_Policy pragma D.3(3), see L(3), see L(21).
Log A.5.1(4), see G.1.2(4), see G.1.2(3).
Logical B.5.
logical operator 4.5.1.
See also not operator 4.5.6.
logical_operator 4.5.
Long 4.9(43), see B.3(43), see B.3(7).
Long_Binary B.4.
long_double B.3.
Long_Float 3.5.7(15), see 3.5.7(16), see 3.5.7(15), see 3.5.7(16), see 3.5.7(17).
Long_Floating B.4.
Long_Integer 3.5.4(22), see 3.5.4(25), see 3.5.4(22), see 3.5.4(25), see 3.5.4(28).
Look_Ahead A.10.1.
loop parameter 5.5.
loop_parameter_specification 5.5.
used 5.5(3), see P(3), see P(1).
loop_statement 5.5.
used 5.1(5), see P(5), see P(1).
low line 2.1.
low-level programming C.
Low_Limit 3.3.1.
Low_Line A.3.3.
Low_Order_First 13.5.3(2), see B.4(2), see B.4(25).
lower bound
of a range 3.5.
lower-case letter
a category of Character A.3.2.
lower_case_identifier_letter 2.1.
Lower_Case_Map A.4.6.
Lower_Set A.4.6.
ΓòÉΓòÉΓòÉ 43. index ΓòÉΓòÉΓòÉ
Machine attribute A.5.3(60), see K(60), see K(119).
machine code insertion 13.8(1), see C.1(1), see C.1(2).
machine numbers
of a floating point type 3.5.7.
Machine_Code J.1.
child of System 13.8.
Machine_Emax attribute A.5.3(8), see K(8), see K(123).
Machine_Emin attribute A.5.3(7), see K(7), see K(125).
Machine_Mantissa attribute A.5.3(6), see K(6), see K(127).
Machine_Overflows attribute A.5.3(12), see A.5.4(12), see A.5.4(4),
K(129), K(129), K(131).
Machine_Radix attribute A.5.3(2), see A.5.4(2), see A.5.4(2),
K(133), K(133), K(135).
Machine_Radix clause 13.3(7), see F.1(7), see F.1(1).
Machine_Rounds attribute A.5.3(11), see A.5.4(11), see A.5.4(3),
K(137), K(137), K(139).
macro
See generic unit 12.
Macron A.3.3.
Main 10.1.1(33), see 11.4.2(10)
main subprogram
for a partition 10.2.
Major 3.5.1.
Male 3.2.2.
malloc
See allocator 4.8.
Maps
child of Ada.Strings A.4.2.
Mark_Release_Pool_Type 13.11.
marshalling E.4.
Masculine_Ordinal_Indicator A.3.3.
Mask 4.7.
Mass 3.5.7(21), see 12.5(21), see 12.5(13).
master 7.6.1.
match
a character to a pattern character A.4.2.
a character to a pattern character, with
respect to a character mapping function A.4.2.
a string to a pattern string A.4.2.
matching components 4.5.2.
Matrix 3.6.
Matrix_Rec 3.7.
Max 3.3.2.
Max attribute 3.5(19), see K(19), see K(141).
Max_Base_Digits 3.5.7(6), see 13.7(6), see 13.7(8).
named number in package System 13.7.
Max_Binary_Modulus 3.5.4(7), see 13.7(7), see 13.7(7).
named number in package System 13.7.
Max_Decimal_Digits F.2.
Max_Delta F.2.
Max_Digits 3.5.7(6), see 13.7(6), see 13.7(8).
named number in package System 13.7.
Max_Digits_Binary B.4.
Max_Digits_Long_Binary B.4.
Max_Image_Width A.5.2(13), see A.5.2(13), see A.5.2(25).
Max_Int 3.5.4(14), see 13.7(14), see 13.7(6).
named number in package System 13.7.
Max_Length A.4.4.
Max_Line_Size 3.3.2.
Max_Mantissa 13.7.
named number in package System 13.7.
Max_Nonbinary_Modulus 3.5.4(7), see 13.7(7), see 13.7(7).
named number in package System 13.7.
Max_Scale F.2.
Max_Size_In_Storage_Elements attribute 13.11.1,
K.
maximum box error
for a component of the result of evaluating
a complex function G.2.6.
maximum line length A.10.
maximum page length A.10.
maximum relative error
for a component of the result of evaluating
a complex function G.2.6.
for the evaluation of an elementary function G.2.4.
Medium 13.3.
Mega 4.9.
Membership A.4.1.
membership test 4.5.2.
Memory_Size 13.7.
mentioned in a with_clause 10.1.2.
message
See dispatching call 3.9.2.
Message_Procedure 3.10.
method
See dispatching subprogram 3.9.2.
metrics 1.1.2(35), see C.3.1(15), see C.7.2(35), see C.3.1(15), see C.7.2(20),
D(2), D.5(13), D.6(2), D.5(13), D.6(4),
D.8(37), D.9(9), D.12(37), D.9(9), D.12(6).
Micro_Sign A.3.3.
Microseconds D.8.
Middle_Dot A.3.3.
Midweek 3.4.
Milliseconds D.8.
Min attribute 3.5(16), see K(16), see K(147).
Min_Cell 6.1.
Min_Delta F.2.
Min_Int 3.5.4(14), see 13.7(14), see 13.7(6).
named number in package System 13.7.
Min_Scale F.2.
Minimum 8.5.4.
minus 2.1.
minus operator 4.4(1), see 4.5.3(1), see 4.5.4(1), see 4.5.3(1), see 4.5.4(1).
Mix 12.5.3.
Mix_Code 13.4.
Mixed 3.5.1.
mixed-language programs B(1), see C.1(1), see C.1(4).
mod operator 4.4(1), see 4.5.5(1), see 4.5.5(1).
mod_clause J.8.
used 13.5.1(2), see P(2), see P(1).
mode 6.1(16), 8.5(7), 13.5.1(16), 8.5(7), 13.5.1(26),
A.8.1(9), A.8.4(9), see A.10.1(9), A.8.4(9), see A.10.1(12),
A.12.1.
used 6.1(15), see 12.4(2), see P(15), see 12.4(2), see P(1).
mode conformance 6.3.1.
required 8.5.4(4), see 12.5.4(5), see 12.6(4), see 12.5.4(5), see 12.6(7),
12.6.
mode of operation
nonstandard 1.1.5.
standard 1.1.5.
Mode_Error A.8.1(15), A.8.4(18), see A.10.1(15), A.8.4(18), see A.10.1(85),
A.12.1(26), see A.13(26), see A.13(4).
Mode_Mask 13.5.1.
Model attribute A.5.3(68), see G.2.2(7), see K(68), see G.2.2(7), see K(151).
model interval G.2.1.
associated with a value G.2.1.
model number G.2.1.
model-oriented attributes
of a floating point subtype A.5.3.
Model_Emin attribute A.5.3(65), see G.2.2(65), see G.2.2(4),
K.
Model_Epsilon attribute A.5.3(66), see K(66), see K(157).
Model_Mantissa attribute A.5.3(64), see G.2.2(64), see G.2.2(3),
K.
Model_Small attribute A.5.3(67), see K(67), see K(161).
modular type 3.5.4.
modular_type_definition 3.5.4.
used 3.5.4(2), see P(2), see P(1).
Modular_IO A.10.1.
module
See package 7.
modulus G.1.1.
of a modular type 3.5.4.
Modulus attribute 3.5.4(17), see K(17), see K(163).
Money 3.5.9(28), see F.1(28), see F.1(4).
Month 9.6.
Month_Number 9.6.
Move A.4.3.
multi-dimensional array 3.6.
Multiplication_Sign A.3.3.
multiply 2.1.
multiply operator 4.4(1), see 4.5.5(1), see 4.5.5(1).
multiplying operator 4.5.5.
multiplying_operator 4.5.
used 4.4(5), see P(5), see P(1).
MW A.3.3.
My_Read 13.3.
My_Write 8.5.4(14), see 13.13.2(14), see 13.13.2(40).
ΓòÉΓòÉΓòÉ 44. index ΓòÉΓòÉΓòÉ
n-dimensional array_aggregate 4.3.3.
NAK A.3.3.
name 4.1(2), 13.7(4), 13.11.2(2), 13.7(4), 13.11.2(3),
A.8.1(9), see A.8.4(9), see A.10.1(9), see A.8.4(9), see A.10.1(12),
A.12.1.
used 2.8(3), 3.2.2(4), 4.1(3), 3.2.2(4), 4.1(4),
4.1(5), 4.1(6), 4.4(5), 4.1(6), 4.4(7),
4.6(2), 5.2(2), 5.7(2), 5.2(2), 5.7(2),
5.8(2), 6.3.2(3), 6.4(2), 6.3.2(3), 6.4(2),
6.4(3), 6.4(6), 8.4(3), 6.4(6), 8.4(3),
8.5.1(2), 8.5.2(2), 8.5.3(2), 8.5.2(2), 8.5.3(2),
8.5.4(2), 8.5.5(2), 9.5.3(2), 8.5.5(2), 9.5.3(2),
9.5.4(2), 9.8(2), 10.1.1(2), 9.8(2), 10.1.1(8),
10.1.2(4), 10.2.1(3), 10.2.1(4), 10.2.1(3), 10.2.1(14),
10.2.1(20), see 10.2.1(21), see 10.2.1(20), see 10.2.1(21), see 10.2.1(22),
11.2(5), 11.3(2), 11.5(5), 11.3(2), 11.5(4),
12.3(2), 12.3(5), 12.6(2), 12.3(5), 12.6(4),
12.7(2), 13.1(3), 13.3(2), 13.1(3), 13.3(2),
C.3.1(2), C.3.1(4), E.2.1(2), C.3.1(4), E.2.1(3),
E.2.2(3), E.2.3(3), E.2.3(3), E.2.3(3), E.2.3(5),
H.3.2(3), L(2), L(3), L(2), L(6),
L(10), L(11), L(10), L(11), L(12),
L(15), L(16), L(15), L(16), L(17),
L(26), L(28), L(26), L(28), L(30),
L(31), L(34), L(31), L(34), L(36),
P.
[partial] 3.1.
of (a view of) an entity 3.1.
of a pragma 2.8.
of an external file A.7.
name resolution rules 1.1.2.
Name_Error A.8.1(15), A.8.4(18), see A.10.1(15), A.8.4(18), see A.10.1(85),
A.12.1(26), see A.13(26), see A.13(4).
Name_Server E.4.2.
named association 6.4(7), see 12.3(7), see 12.3(6).
named component association 4.3.1.
named discriminant association 3.7.1.
named entry index 9.5.2.
named number 3.3.
named type 3.2.1.
named_array_aggregate 4.3.3.
used 4.3.3(2), see P(2), see P(1).
Names
child of Ada.Interrupts C.3.2.
names of special_characters 2.1.
Nanoseconds D.8.
Native_Binary B.4.
Natural 3.5.4(12), see 3.5.4(13), see A.1(12), see 3.5.4(13), see A.1(13).
NBH A.3.3.
needed
of a compilation unit by another 10.2.
remote call interface E.2.3.
shared passive library unit E.2.1.
needed component
extension_aggregate record_component_association_list
4.3.2.
record_aggregate record_component_association_list
4.3.1.
NEL A.3.3.
new
See allocator 4.8.
New_Char_Array B.3.1.
New_Line A.10.1.
New_Page A.10.1.
New_String B.3.1.
New_Tape E.4.2.
Next 8.5.4.
Next_Action 9.1.
Next_Frame 6.1.
Next_Lexeme 9.1.
Next_Work_Item 9.1.
Ninety_Six 3.6.3.
No_Break_Space A.3.3.
Node 12.5.4.
nominal subtype 3.3(23), see 3.3.1(23), see 3.3.1(8).
associated with a type_conversion 4.6.
associated with a dereference 4.1.
associated with an indexed_component 4.1.1.
of a component 3.6.
of a formal parameter 6.1.
of a generic formal object 12.4.
of a record component 3.8.
of the result of a function_call 6.4.
non-normative
See informative 1.1.2.
nondispatching call
on a dispatching operation 3.9.2.
nonexistent 13.11.2(10), see 13.11.2(10), see 13.11.2(16).
nongraphic character 3.5.
nonlimited type 7.5.
becoming nonlimited 7.3.1(5), see 7.5(5), see 7.5(16).
nonstandard integer type 3.5.4.
nonstandard mode 1.1.5.
nonstandard real type 3.5.6.
normal completion 7.6.1.
normal library unit E.2.
normal state of an object 11.6(6), see 13.9.1(6), see 13.9.1(4).
[partial] 9.8(21), see A.13(21), see A.13(17).
Normalize_Scalars pragma H.1(3), see L(3), see L(22).
normalized exponent A.5.3.
normalized number A.5.3.
normative 1.1.2.
not equal operator 4.4(1), see 4.5.2(1), see 4.5.2(1).
not in (membership test) 4.4(1), see 4.5.2(1), see 4.5.2(2).
not operator 4.4(1), see 4.5.6(1), see 4.5.6(3).
Not_Sign A.3.3.
notes 1.1.2.
notwithstanding 10.1.6(2), see B.1(22), see B.1(2), see B.1(22), see B.1(38),
C.3.1(19), see E.2.1(19), see E.2.1(8),
E.2.1(11), see E.2.3(18), see J.3(11), see E.2.3(18), see J.3(6).
NUL A.3.3(5), see B.3(20), see J.5(5), see B.3(20), see J.5(4).
null access value 4.2.
null array 3.6.1.
null constraint 3.2.
null pointer
See null access value 4.2.
null range 3.5.
null record 3.8.
null slice 4.1.2.
null string literal 2.6.
null value
of an access type 3.10.
Null_Address 13.7.
constant in System 13.7.
Null_Bounded_String A.4.4.
Null_Key 7.3.1(15), see 7.4(15), see 7.4(13).
Null_Occurrence 11.4.1.
Null_Ptr B.3.1.
Null_Set A.4.2(5), see A.4.7(5), see A.4.7(5).
null_statement 5.1.
used 5.1(4), see P(4), see P(1).
Null_Task_ID C.7.1.
Null_Unbounded_String A.4.5.
Null_Id 11.4.1.
Num A.10.1(52), see A.10.1(57), see A.10.1(52), see A.10.1(57), see A.10.1(63),
A.10.1(68), see A.10.1(73), see B.4(68), see A.10.1(73), see B.4(31),
F.3.3.
number sign 2.1.
Number_Base A.10.1(6), see A.10.8(6), see A.10.8(3).
number_declaration 3.3.2.
used 3.1(3), see P(3), see P(1).
Number_Sign A.3.3.
numeral 2.4.1.
used 2.4.1(2), see 2.4.1(4), see 2.4.2(2), see 2.4.1(4), see 2.4.2(3),
P.
Numeric B.4.
numeric type 3.5.
Numeric_Error J.6.
numeric_literal 2.4.
used 4.4(7), see P(7), see P(1).
Numerics G.
child of Ada A.5.
ΓòÉΓòÉΓòÉ 45. index ΓòÉΓòÉΓòÉ
object 3.3(2), see 13.7.2(2), see 13.11.2(2), see 13.7.2(2), see 13.11.2(3),
N.
[partial] 3.2.
object-oriented programming (OOP)
See dispatching operations of tagged types 3.9.2.
See tagged types and type extensions 3.9.
object_declaration 3.3.1.
used 3.1(3), see P(3), see P(1).
Object_Pointer 13.7.2.
object_renaming_declaration 8.5.1.
used 8.5(2), see P(2), see P(1).
obsolescent feature J.
occur immediately within 8.1(13)
occurrence
of an interrupt C.3.
octal
literal 2.4.2.
octal literal 2.4.2.
On_Stacks 12.8.
On_Vectors 12.1(24), see 12.2(24), see 12.2(9).
one's complement
modular types 3.5.4.
one-dimensional array 3.6.
only as a completion
entry_body 9.5.2.
OOP (object-oriented programming)
See dispatching operations of tagged types 3.9.2.
See tagged types and type extensions 3.9.
opaque type
See private types and private extensions 7.3.
Open 7.5(19), 7.5(20), 11.4.2(19), 7.5(20), 11.4.2(3),
11.4.2(6), A.8.1(7), see A.8.4(6), A.8.1(7), see A.8.4(7),
A.10.1(10), see A.12.1(10), see A.12.1(9).
open alternative 9.7.1.
open entry 9.5.3.
of a protected object 9.5.3.
of a task 9.5.3.
operand
of a type_conversion 4.6.
of a qualified_expression 4.7.
operand interval G.2.1.
operand type
of a type_conversion 4.6.
operates on a type 3.2.3.
operator 6.6.
& 4.4(1), see 4.5.3(1), see 4.5.3(3).
* 4.4(1), see 4.5.5(1), see 4.5.5(1).
** 4.4(1), see 4.5.6(1), see 4.5.6(7).
+ 4.4(1), see 4.5.3(1), see 4.5.4(1), see 4.5.3(1), see 4.5.4(1).
= 4.4(1), see 4.5.2(1), see 4.5.2(1).
- 4.4(1), see 4.5.3(1), see 4.5.4(1), see 4.5.3(1), see 4.5.4(1).
/ 4.4(1), see 4.5.5(1), see 4.5.5(1).
/= 4.4(1), see 4.5.2(1), see 4.5.2(1).
< 4.4(1), see 4.5.2(1), see 4.5.2(1).
<= 4.4(1), see 4.5.2(1), see 4.5.2(1).
> 4.4(1), see 4.5.2(1), see 4.5.2(1).
>= 4.4(1), see 4.5.2(1), see 4.5.2(1).
abs 4.4(1), see 4.5.6(1), see 4.5.6(1).
ampersand 4.4(1), see 4.5.3(3)
and 4.4(1), see 4.5.1(2)
binary 4.5.
binary adding 4.5.3.
concatenation 4.4(1), see 4.5.3(1), see 4.5.3(3).
divide 4.4(1), see 4.5.5(1), see 4.5.5(1).
equal 4.4(1), see 4.5.2(1), see 4.5.2(1).
equality 4.5.2.
exponentiation 4.4(1), see 4.5.6(1), see 4.5.6(7).
greater than 4.4(1), see 4.5.2(1), see 4.5.2(1).
greater than or equal 4.4(1), see 4.5.2(1), see 4.5.2(1).
highest precedence 4.5.6.
less than 4.4(1), see 4.5.2(1), see 4.5.2(1).
less than or equal 4.4(1), see 4.5.2(1), see 4.5.2(1).
logical 4.5.1.
minus 4.4(1), see 4.5.3(1), see 4.5.4(1), see 4.5.3(1), see 4.5.4(1).
mod 4.4(1), see 4.5.5(1), see 4.5.5(1).
multiply 4.4(1), see 4.5.5(1), see 4.5.5(1).
multiplying 4.5.5.
not 4.4(1), see 4.5.6(1), see 4.5.6(3).
not equal 4.4(1), see 4.5.2(1), see 4.5.2(1).
or 4.4(1), see 4.5.1(1), see 4.5.1(2).
ordering 4.5.2.
plus 4.4(1), see 4.5.3(1), see 4.5.4(1), see 4.5.3(1), see 4.5.4(1).
predefined 4.5.
relational 4.5.2.
rem 4.4(1), see 4.5.5(1), see 4.5.5(1).
times 4.4(1), see 4.5.5(1), see 4.5.5(1).
unary 4.5.
unary adding 4.5.4.
user-defined 6.6.
xor 4.4(1), see 4.5.1(1), see 4.5.1(2).
operator precedence 4.5.
operator_symbol 6.1.
used 4.1(3), 4.1.3(3), see 6.1(3), 4.1.3(3), see 6.1(5),
6.1(11), see P(11), see P(1).
optimization 11.5(29), see 11.6(29), see 11.6(1).
Optimize pragma 2.8(23), see L(23), see L(23).
Option 12.5.3.
or else (short-circuit control form) 4.4,
4.5.1.
or operator 4.4(1), see 4.5.1(1), see 4.5.1(2).
ordering operator 4.5.2.
ordinary fixed point type 3.5.9(1), see 3.5.9(1), see 3.5.9(8).
ordinary_fixed_point_definition 3.5.9.
used 3.5.9(2), see P(2), see P(1).
Origin 3.9.1(12)
OSC A.3.3.
other_control_function 2.1.
used 2.1(2), see P(2), see P(1).
Other_Procedure 3.10.
output A.6.
Output attribute 13.13.2(19), see 13.13.2(19), see 13.13.2(29),
K(165), K(165), K(169).
Output clause 13.3(7), see 13.13.2(7), see 13.13.2(36).
overall interpretation
of a complete context 8.6.
Overflow_Check 11.5.
[partial] 3.5.4(20), see 4.4(11), 5.4(20), see 4.4(11), 5.4(13),
G.2.1(11), see G.2.2(7), see G.2.3(11), see G.2.2(7), see G.2.3(25),
G.2.4(2), G.2.6(2), G.2.6(3).
overload resolution 8.6.
overloadable 8.3.
overloaded 8.3.
enumeration literal 3.5.1.
overloading rules 1.1.2(26), see 8.6(26), see 8.6(2).
override 8.3(9), see 12.3(9), see 12.3(17).
a primitive subprogram 3.2.3.
Overwrite A.4.3(27), see A.4.3(28), see A.4.4(27), see A.4.3(28), see A.4.4(62),
A.4.4(63), see A.4.5(57), see A.4.5(63), see A.4.5(57), see A.4.5(58).
ΓòÉΓòÉΓòÉ 46. index ΓòÉΓòÉΓòÉ
P 9.2(11), see 12.5.3(11), see 12.5.4(11), see 12.5.3(11), see 12.5.4(8).
Pack pragma 13.2(3), see L(3), see L(24).
Package 7(1), see N(1), see N(25).
package instance 12.3.
package_body 7.2.
used 3.11(6), see 10.1.1(7), see P(6), see 10.1.1(7), see P(1).
package_body_stub 10.1.3.
used 10.1.3(2), see P(2), see P(1).
package_declaration 7.1.
used 3.1(3), see 10.1.1(5), see P(3), see 10.1.1(5), see P(1).
package_renaming_declaration 8.5.3.
used 8.5(2), see 10.1.1(6), see P(2), see 10.1.1(6), see P(1).
package_specification 7.1.
used 7.1(2), see 12.1(4), see P(2), see 12.1(4), see P(1).
packed 13.2.
Packed_Decimal B.4.
Packed_Descriptor 13.6.
Packed_Format B.4.
Packed_Signed B.4.
Packed_Unsigned B.4.
packing
aspect of representation 13.2.
padding bits 13.1.
Page 13.3(80), see A.10.1(80), see A.10.1(39).
Page pragma 2.8(22), see L(22), see L(25).
page terminator A.10.
Page_Length A.10.1.
Page_Num 3.5.4.
Painted_Point 3.9.1.
Pair 6.4.
parallel processing
See task 9.
Parallel_Simulation A.5.2.
parameter
See also discriminant 3.7.
See also loop parameter 5.5.
See formal parameter 6.1.
See generic formal parameter 12.
parameter assigning back 6.4.1.
parameter copy back 6.4.1.
parameter mode 6.1.
parameter passing 6.4.1.
parameter_and_result_profile 6.1.
used 3.10(5), see 6.1(4), see P(5), see 6.1(4), see P(1).
parameter_association 6.4.
used 6.4(4), see P(4), see P(1).
parameter_profile 6.1.
used 3.10(5), 6.1(4), 9.5.2(5), 6.1(4), 9.5.2(2),
9.5.2(3), see 9.5.2(6), see P(3), see 9.5.2(6), see P(1).
parameter_specification 6.1.
used 6.1(14), see P(14), see P(1).
Parameterless_Handler C.3.2.
Params_Stream_Type E.5.
Parent 10.1.3(20), see 10.1.3(21), see 10.1.3(20), see 10.1.3(21), see 10.1.3(23).
parent body
of a subunit 10.1.3.
parent declaration
of a library_item 10.1.1.
of a library unit 10.1.1.
parent subtype 3.4.
parent type 3.4.
parent unit
of a library unit 10.1.1.
parent_unit_name 10.1.1.
used 6.1(5), see 6.1(7), 7.1(5), see 6.1(7), 7.1(3),
7.2(2), see 10.1.3(7), see P(2), see 10.1.3(7), see P(1).
Parser 9.1.
part
of an object or value 3.2.
partial view
of a type 7.3.
partition 10.2(2), see N(2), see N(26).
partition building 10.2.
partition communication subsystem (PCS) E.5.
Partition_Check
[partial] E.4.
Partition_ID E.5.
Partition_ID attribute E.1(9), see K(9), see K(173).
pass by copy 6.2.
pass by reference 6.2.
passive partition E.1.
PCS (partition communication subsystem) E.5.
pending interrupt occurrence C.3.
per-object constraint 3.8.
per-object expression 3.8.
Percent J.5.
Percent_Sign A.3.3.
perfect result set G.2.3.
periodic task
See delay_until_statement 9.6.
example 9.6.
Peripheral 3.8.1.
Peripheral_Ref 3.10.
Person 3.10.1(19), see 3.10.1(19), see 3.10.1(22).
Person_Name 3.10.1.
Pi A.5.
Pic_String F.3.3.
Picture F.3.3.
picture String
for edited output F.3.1.
Picture_Error F.3.3.
Pilcrow_Sign A.3.3.
plain_char B.3.
PLD A.3.3.
PLU A.3.3.
plus operator 4.4(1), see 4.5.3(1), see 4.5.4(1), see 4.5.3(1), see 4.5.4(1).
plus sign 2.1.
Plus_Minus_Sign A.3.3.
Plus_Sign A.3.3.
PM A.3.3.
point 1(2.15), see 3.9(2.15), see 3.9(32).
pointer B.3.2.
See access value 3.10.
See type System.Address 13.7.
pointer type
See access type 3.10.
Pointer_Error B.3.2.
Pointers
child of Interfaces.C B.3.2.
polymorphism 3.9(1), see 3.9.2(1), see 3.9.2(1).
pool element 3.10(7), see 13.11(7), see 13.11(11).
pool type 13.11.
pool-specific access type 3.10(7), see 3.10(7), see 3.10(8).
Pop 12.8(3), see 12.8(7), see 12.8(3), see 12.8(7), see 12.8(14).
Pos attribute 3.5.5(2), see K(2), see K(175).
position 13.5.1.
used 13.5.1(3), see P(3), see P(1).
Position attribute 13.5.2(2), see K(2), see K(179).
position number 3.5.
of an enumeration value 3.5.1.
of an integer value 3.5.4.
positional association 6.4(7), see 12.3(7), see 12.3(6).
positional component association 4.3.1.
positional discriminant association 3.7.1.
positional_array_aggregate 4.3.3.
used 4.3.3(2), see P(2), see P(1).
Positive 3.5.4(12), see 3.5.4(13), see 3.6.3(12), see 3.5.4(13), see 3.6.3(3),
A.1.
Positive_Count A.8.4(4), A.10(4), A.10(10),
A.10.1(5), see A.12.1(5), see A.12.1(7).
possible interpretation 8.6.
for direct_names 8.3.
for selector_names 8.3.
post-compilation error 1.1.2.
post-compilation rules 1.1.2(29), see 10.1.3(29), see 10.1.3(15),
10.1.5(8), see 10.2(8), see 10.2(2),
12.3(19), 13.12(19), 13.12(8),
D.2.2(4), D.3(4), D.3(5),
D.4(5), E(5), E(2),
E.1(2), E.2.1(2), E.2.1(10),
E.2.3(17), see H.1(17), see H.1(4),
H.3.1.
potentially blocking operation 9.5.1.
Abort_Task C.7.1.
delay_statement 9.6(34), see D.9(34), see D.9(5).
remote subprogram call E.4.
RPC operations E.5.
Suspend_Until_True D.10.
potentially use-visible 8.4.
Pound_Sign A.3.3.
Power_16 3.3.2.
Pragma 2.8(1), see 2.8(2), see L(1), see N(1), see 2.8(2), see L(1), see N(27).
pragma argument 2.8.
pragma name 2.8.
pragma, categorization E.2.
Remote_Call_Interface E.2.3.
Remote_Types E.2.2.
Shared_Passive E.2.1.
pragma, configuration 10.1.5.
Locking_Policy D.3.
Normalize_Scalars H.1.
Queuing_Policy D.4.
Restrictions 13.12.
Reviewable H.3.1.
Suppress 11.5.
Task_Dispatching_Policy D.2.2.
pragma, identifier specific to 2.8.
pragma, interfacing
Convention B.1.
Export B.1.
Import B.1.
Linker_Options B.1.
pragma, library unit 10.1.5.
All_Calls_Remote E.2.3.
categorization pragmas E.2.
Elaborate_Body 10.2.1.
Preelaborate 10.2.1.
Pure 10.2.1.
pragma, program unit 10.1.5.
Convention B.1.
Export B.1.
Import B.1.
Inline 6.3.2.
library unit pragmas 10.1.5.
pragma, representation 13.1.
Asynchronous E.4.1.
Atomic C.6.
Atomic_Components C.6.
Controlled 13.11.3.
Convention B.1.
Discard_Names C.5.
Export B.1.
Import B.1.
Pack 13.2.
Volatile C.6.
Volatile_Components C.6.
pragma_argument_association 2.8.
used 2.8(2), see P(2), see P(1).
pragmas
All_Calls_Remote E.2.3(5), see L(5), see L(2).
Asynchronous E.4.1(3), see L(3), see L(3).
Atomic C.6(3), see L(3), see L(4).
Atomic_Components C.6(5), see L(5), see L(5).
Attach_Handler C.3.1(4), see L(4), see L(6).
Controlled 13.11.3(3), see L(3), see L(7).
Convention B.1(7), see L(7), see L(8).
Discard_Names C.5(3), see L(3), see L(9).
Elaborate 10.2.1(20), see L(20), see L(10).
Elaborate_All 10.2.1(21), see L(21), see L(11).
Elaborate_Body 10.2.1(22), see L(22), see L(12).
Export B.1(6), see L(6), see L(13).
Import B.1(5), see L(5), see L(14).
Inline 6.3.2(3), see L(3), see L(15).
Inspection_Point H.3.2(3), see L(3), see L(16).
Interrupt_Handler C.3.1(2), see L(2), see L(17).
Interrupt_Priority D.1(5), see L(5), see L(18).
Linker_Options B.1(8), see L(8), see L(19).
List 2.8(21), see L(21), see L(20).
Locking_Policy D.3(3), see L(3), see L(21).
Normalize_Scalars H.1(3), see L(3), see L(22).
Optimize 2.8(23), see L(23), see L(23).
Pack 13.2(3), see L(3), see L(24).
Page 2.8(22), see L(22), see L(25).
Preelaborate 10.2.1(3), see L(3), see L(26).
Priority D.1(3), see L(3), see L(27).
Pure 10.2.1(14), see L(14), see L(28).
Queuing_Policy D.4(3), see L(3), see L(29).
Remote_Call_Interface E.2.3(3), see L(3), see L(30).
Remote_Types E.2.2(3), see L(3), see L(31).
Restrictions 13.12(3), see L(3), see L(32).
Reviewable H.3.1(3), see L(3), see L(33).
Shared_Passive E.2.1(3), see L(3), see L(34).
Storage_Size 13.3(63), see L(63), see L(35).
Suppress 11.5(4), see L(4), see L(36).
Task_Dispatching_Policy D.2.2(2), see L(2), see L(37).
Volatile C.6(4), see L(4), see L(38).
Volatile_Components C.6(6), see L(6), see L(39).
precedence of operators 4.5.
Pred attribute 3.5(25), see K(25), see K(181).
predefined environment A.
predefined exception 11.1.
predefined library unit
See language-defined library units
predefined operation
of a type 3.2.3.
predefined operations
of a discrete type 3.5.5.
of a fixed point type 3.5.10.
of a floating point type 3.5.8.
of a record type 3.8.
of an access type 3.10.2.
of an array type 3.6.2.
predefined operator 4.5.
[partial] 3.2.1.
predefined type 3.2.1.
See language-defined types
preelaborable
of an elaborable construct 10.2.1.
Preelaborate pragma 10.2.1(3), see L(3), see L(26).
preelaborated 10.2.1.
[partial] 10.2.1(11), see E.2.1(11), see E.2.1(9).
preempted task D.2.1.
preemptible resource D.2.1.
preference
for root numeric operators and ranges 8.6.
preference control
See requeue 9.5.4.
prefix 4.1.
used 4.1.1(2), see 4.1.2(2), see 4.1.3(2), see 4.1.2(2), see 4.1.3(2),
4.1.4(2), see 4.1.4(4), see 6.4(2), see 4.1.4(4), see 6.4(2),
6.4(3), P(3), P(1).
prescribed result
for the evaluation of a complex arithmetic operation
G.1.1.
for the evaluation of a complex elementary function
G.1.2.
for the evaluation of an elementary function A.5.1.
primary 4.4.
used 4.4(6), see P(6), see P(1).
primitive function A.5.3.
primitive operation
[partial] 3.2.
primitive operations N.
of a type 3.2.3.
primitive operator
of a type 3.2.3.
primitive subprograms
of a type 3.2.3.
Print_Header 6.1.
Priority 13.7(16), see D.1(10), see D.1(16), see D.1(10), see D.1(15).
priority inheritance D.1.
priority inversion D.2.2.
priority of an entry call D.4.
Priority pragma D.1(3), see L(3), see L(27).
private declaration of a library unit 10.1.1.
private descendant
of a library unit 10.1.1.
private extension 3.2(4), see 3.9(2), see 3.9.1(4), see 3.9(2), see 3.9.1(1),
N.
[partial] 7.3.
private library unit 10.1.1.
private operations 7.3.1.
private part 8.2.
of a package 7.1.
of a protected unit 9.4.
of a task unit 9.1.
private type 3.2(4), see N(4), see N(30).
[partial] 7.3.
private types and private extensions 7.3.
private_extension_declaration 7.3.
used 3.2.1(2), see P(2), see P(1).
private_type_declaration 7.3.
used 3.2.1(2), see P(2), see P(1).
Probability 3.5.7.
procedure 6.
procedure instance 12.3.
procedure_call_statement 6.4.
used 5.1(4), see P(4), see P(1).
processing node E.
Producer 9.11(2), see 9.11(2), see 9.11(3).
profile 6.1.
associated with a dereference 4.1.
fully conformant 6.3.1.
mode conformant 6.3.1.
subtype conformant 6.3.1.
type conformant 6.3.1.
profile resolution rule
name with a given expected profile 8.6.
Prog B.4.
program 10.2(1), see N(1), see N(32).
program execution 10.2.
program library
See library 10(2), see 10.1.4(2), see 10.1.4(9).
Program unit 10.1(1), see N(1), see N(31).
program unit pragma 10.1.5.
Convention B.1.
Export B.1.
Import B.1.
Inline 6.3.2.
library unit pragmas 10.1.5.
Program_Error A.1.
raised by failure of run-time check
1.1.3(20), 1.1.5(8), 1.1.5(20), 1.1.5(8), 1.1.5(12),
3.5.5(8), 3.10.2(29), 3.11(8), 3.10.2(29), 3.11(14),
4.6(57), 6.2(12), 6.4(57), 6.2(12), 6.4(11),
6.5(20), 7.6.1(15), 7.6.1(20), 7.6.1(15), 7.6.1(16),
7.6.1(17), 7.6.1(18), 9.4(17), 7.6.1(18), 9.4(20),
9.5.1(17), 9.5.3(7), 9.7.1(17), 9.5.3(7), 9.7.1(21),
9.8(20), 10.2(26), 11.1(20), 10.2(26), 11.1(4),
11.5(19), 13.7.1(16), 13.9.1(19), 13.7.1(16), 13.9.1(9),
13.11.2(13), see 13.11.2(14), see A.7(13), see 13.11.2(14), see A.7(14),
C.3.1(10), C.3.1(11), C.3.2(10), C.3.1(11), C.3.2(17),
C.3.2(20), C.3.2(21), C.3.2(20), C.3.2(21), C.3.2(22),
C.7.1(15), C.7.1(17), C.7.2(15), C.7.1(17), C.7.2(13),
D.3(13), D.5(9), D.5(13), D.5(9), D.5(11),
D.10(10), D.11(8), E.1(10), D.11(8), E.1(10),
E.3(6), E.4(18), J.7.1(6), E.4(18), J.7.1(7).
Program_Status_Word 13.5.1.
propagate 11.4.
an exception occurrence by an execution, to a dynamically
enclosing execution 11.4.
proper_body 3.11.
used 3.11(5), see 10.1.3(7), see P(5), see 10.1.3(7), see P(1).
protected action 9.5.1.
complete 9.5.1.
start 9.5.1.
protected calling convention 6.3.1.
protected declaration 9.4.
protected entry 9.4.
protected function 9.5.1.
protected object 9(3), see 9.4(3), see 9.4(1).
protected operation 9.4.
protected procedure 9.5.1.
protected subprogram 9.4(1), see 9.5.1(1), see 9.5.1(1).
Protected type N.
protected unit 9.4.
protected_body 9.4.
used 3.11(6), see P(6), see P(1).
protected_body_stub 10.1.3.
used 10.1.3(2), see P(2), see P(1).
protected_definition 9.4.
used 9.4(2), see 9.4(3), see P(2), see 9.4(3), see P(1).
protected_element_declaration 9.4.
used 9.4(4), see P(4), see P(1).
protected_operation_declaration 9.4.
used 9.4(4), see 9.4(6), see P(4), see 9.4(6), see P(1).
protected_operation_item 9.4.
used 9.4(7), see P(7), see P(1).
protected_type_declaration 9.4.
used 3.2.1(3), see P(3), see P(1).
ptrdiff_t B.3.
PU1 A.3.3.
PU2 A.3.3.
public declaration of a library unit 10.1.1.
public descendant
of a library unit 10.1.1.
public library unit 10.1.1.
pure 10.2.1.
Pure pragma 10.2.1(14), see L(14), see L(28).
Push 6.3(9), see 12.8(3), see 12.8(6), see 12.8(9), see 12.8(3), see 12.8(6), see 12.8(14).
Put 6.4(26), 10.1.1(30), see A.10.1(26), 10.1.1(30), see A.10.1(42),
A.10.1(48), see A.10.1(55), see A.10.1(48), see A.10.1(55), see A.10.1(60),
A.10.1(66), see A.10.1(67), see A.10.1(66), see A.10.1(67), see A.10.1(71),
A.10.1(72), see A.10.1(76), see A.10.1(72), see A.10.1(76), see A.10.1(77),
A.10.1(82), see A.10.1(83), see F.3.3(82), see A.10.1(83), see F.3.3(14),
F.3.3(15), F.3.3(16), G.1.3(15), F.3.3(16), G.1.3(7),
G.1.3.
Put_Item 12.6.
Put_Line A.10.1.
Put_List 12.6.
ΓòÉΓòÉΓòÉ 47. Index ΓòÉΓòÉΓòÉ
qualified_expression 4.7.
used 4.4(7), see 4.8(2), see 13.8(2), see P(7), see 4.8(2), see 13.8(2), see P(1).
Query J.5.
Question 3.6.3(7), see A.3.3(7), see A.3.3(10).
queuing policy D.4(1), see D.4(1), see D.4(6).
Queuing_Policy pragma D.4(3), see L(3), see L(29).
Quotation A.3.3.
quotation mark 2.1.
quoted string
See string_literal 2.6.
Quotient_Type F.2.
ΓòÉΓòÉΓòÉ 48. index ΓòÉΓòÉΓòÉ
R 12.5.3(15), see 12.5.4(15), see 12.5.4(13).
R_Brace J.5.
R_Bracket J.5.
Rad_To_Deg 4.9.
Rainbow 3.2.2(15), see 3.5.1(15), see 3.5.1(16).
raise
an exception 11(1), see 11.3(4), see N(1), see 11.3(4), see N(18).
an exception occurrence 11.4.
Raise_Exception 11.4.1.
raise_statement 11.3.
used 5.1(4), see P(4), see P(1).
Random 6.1(38), see A.5.2(8), see A.5.2(38), see A.5.2(8), see A.5.2(20).
random number A.5.2.
Random_Coin A.5.2(58)
Random_Die A.5.2.
range 3.5(3), see 3.5(3), see 3.5(4).
used 3.5(2), see 3.6(6), see 3.6.1(2), see 3.6(6), see 3.6.1(3),
4.4(3), see P(3), see P(1).
of a scalar subtype 3.5.
Range attribute 3.5(14), see 3.6.2(14), see 3.6.2(7),
K(187), K(187), K(189).
Range(N) attribute 3.6.2(8), see K(8), see K(185).
range_attribute_designator 4.1.4.
used 4.1.4(4), see P(4), see P(1).
range_attribute_reference 4.1.4.
used 3.5(3), see P(3), see P(1).
Range_Check 11.5.
[partial] 3.2.2(11), see 3.5(24), 3.5(11), see 3.5(24), 3.5(27),
3.5(43), 3.5(44), 3.5(43), 3.5(44), 3.5(51),
3.5(55), 3.5.5(7), 3.5.9(55), 3.5.5(7), 3.5.9(19),
4.2(11), 4.3.3(28), 4.5.1(11), 4.3.3(28), 4.5.1(8),
4.5.6(6), 4.5.6(13), 4.6(6), 4.5.6(13), 4.6(28),
4.6(38), 4.6(46), 4.6(38), 4.6(46), 4.6(51),
4.7(4), 13.13.2(35), see A.5.2(4), 13.13.2(35), see A.5.2(39),
A.5.2(40), see A.5.3(26), A.5.3(40), see A.5.3(26), A.5.3(29),
A.5.3(50), see A.5.3(53), A.5.3(50), see A.5.3(53), A.5.3(59),
A.5.3(62), see K(11), K(62), see K(11), K(41),
K(47), K(114), K(47), K(114), K(122),
K(184), K(220), K(184), K(220), K(241).
range_constraint 3.5.
used 3.2.2(6), see 3.5.9(6), see 3.5.9(5),
J.3(2), P(2), P(1).
Rank 12.5(16), see B.5(16), see B.5(31).
Rational 7.1.
Rational_Numbers 7.1(12), see 7.2(10), see 10.1.1(12), see 7.2(10), see 10.1.1(32).
Rational_Numbers.Reduce 10.1.1.
Rational_Numbers.IO 10.1.1.
Rational_IO 10.1.1.
RCI
generic E.2.3.
library unit E.2.3.
package E.2.3.
Re G.1.1.
re-raise statement 11.3.
read 7.5(19), 7.5(20), 9.1(19), 7.5(20), 9.1(24),
9.5.2(33), 9.11(8), 9.11(33), 9.11(8), 9.11(10),
11.4.2(4), 11.4.2(7), 13.13.1(4), 11.4.2(7), 13.13.1(5),
A.8.1(12), A.8.4(12), A.9(12), A.8.4(12), A.9(6),
A.12.1(15), see A.12.1(16), see D.12(15), see A.12.1(16), see D.12(9),
D.12(10), E.5(10), E.5(7).
the value of an object 3.3.
Read attribute 13.13.2(6), see 13.13.2(6), see 13.13.2(14),
K(191), K(191), K(195).
Read clause 13.3(7), see 13.13.2(7), see 13.13.2(36).
ready
a task state 9.
ready queue D.2.1.
ready task D.2.1.
Real 3.5.7(21), see B.5(6), see G.1.1(21), see B.5(6), see G.1.1(2).
real literal 2.4.
real literals 3.5.6.
real time D.8.
real type 3.2(3), see 3.5.6(1), see N(3), see 3.5.6(1), see N(34).
real-time systems C(1), see D(1), see D(1).
Real_Plus 8.5.4.
real_range_specification 3.5.7.
used 3.5.7(2), see 3.5.9(2), see 3.5.9(3),
3.5.9(4), see P(4), see P(1).
Real_Time
child of Ada D.8.
real_type_definition 3.5.6.
used 3.2.1(4), see P(4), see P(1).
Real_IO A.10.9.
receiving stub E.4.
reclamation of storage 13.11.2.
recommended level of support 13.1.
enumeration_representation_clause 13.4.
record_representation_clause 13.5.1.
Address attribute 13.3.
Alignment attribute for objects 13.3.
Alignment attribute for subtypes 13.3.
bit ordering 13.5.3.
Component_Size attribute 13.3.
pragma Pack 13.2.
required in Systems Programming Annex C.2.
Size attribute 13.3(42), see 13.3(42), see 13.3(54).
unchecked conversion 13.9.
with respect to nonstatic expressions 13.1.
record 3.8.
record extension 3.4(5), see 3.9.1(1), see N(5), see 3.9.1(1), see N(35).
record layout
aspect of representation 13.5.
record type 3.8(1), see N(1), see N(36).
record_aggregate 4.3.1.
used 4.3(2), see P(2), see P(1).
record_component_association 4.3.1.
used 4.3.1(3), see P(3), see P(1).
record_component_association_list 4.3.1.
used 4.3.1(2), see 4.3.2(2), see P(2), see 4.3.2(2), see P(1).
record_definition 3.8.
used 3.8(2), see 3.9.1(2), see P(2), see 3.9.1(2), see P(1).
record_extension_part 3.9.1.
used 3.4(2), see P(2), see P(1).
record_representation_clause 13.5.1.
used 13.1(2), see P(2), see P(1).
record_type_definition 3.8.
used 3.2.1(4), see P(4), see P(1).
Red_Blue 3.2.2.
Reference C.3.2(10), see C.7.2(10), see C.7.2(5).
reference parameter passing 6.2.
references 1.2.
Register E.4.2.
Registered_Trade_Mark_Sign A.3.3.
Reinitialize C.7.2.
relation 4.4.
used 4.4(2), see P(2), see P(1).
relational operator 4.5.2.
relational_operator 4.5.
used 4.4(3), see P(3), see P(1).
relaxed mode G.2.
Release 9.4(27), see 9.4(27), see 9.4(29).
execution resource associated with protected object
9.5.1.
rem operator 4.4(1), see 4.5.5(1), see 4.5.5(1).
Remainder attribute A.5.3(45), see K(45), see K(199).
Remainder_Type F.2.
remote access E.1.
remote access type E.2.2.
remote access-to-class-wide type E.2.2.
remote access-to-subprogram type E.2.2.
remote call interface E.2(4), see E.2.3(4), see E.2.3(7).
remote procedure call
asynchronous E.4.1.
remote subprogram E.2.3.
remote subprogram binding E.4.
remote subprogram call E.4.
remote types library unit E.2(4), see E.2.2(4), see E.2.2(4).
Remote_Call_Interface pragma E.2.3(3), see L(3), see L(30).
Remote_Types pragma E.2.2(3), see L(3), see L(31).
Remove E.4.2.
renamed entity 8.5.
renamed view 8.5.
renaming-as-body 8.5.4.
renaming-as-declaration 8.5.4.
renaming_declaration 8.5.
used 3.1(3), see P(3), see P(1).
rendezvous 9.5.2.
Replace_Element A.4.4(27), see A.4.5(27), see A.4.5(21).
Replace_Slice A.4.3(23), see A.4.3(23), see A.4.3(24),
A.4.4(58), see A.4.4(58), see A.4.4(59),
A.4.5(53), see A.4.5(53), see A.4.5(54).
Replicate A.4.4(78), see A.4.4(79), see A.4.4(78), see A.4.4(79), see A.4.4(80).
representation
change of 13.6.
representation aspect 13.1.
representation attribute 13.3.
representation item 13.1.
representation of an object 13.1.
representation pragma 13.1.
Asynchronous E.4.1.
Atomic C.6.
Atomic_Components C.6.
Controlled 13.11.3.
Convention B.1.
Discard_Names C.5.
Export B.1.
Import B.1.
Pack 13.2.
Volatile C.6.
Volatile_Components C.6.
representation-oriented attributes
of a fixed point subtype A.5.4.
of a floating point subtype A.5.3.
representation_clause 13.1.
used 3.8(5), see 3.11(4), see 9.1(5), see 3.11(4), see 9.1(5),
9.4(5), see 9.4(8), P(5), see 9.4(8), P(1).
represented in canonical form A.5.3.
Request 9.1(26), see 9.5.2(26), see 9.5.2(33).
requested decimal precision
of a floating point type 3.5.7.
requeue 9.5.4.
requeue-with-abort 9.5.4.
requeue_statement 9.5.4.
used 5.1(4), see P(4), see P(1).
requires a completion 3.11.1(1), see 3.11.1(1), see 3.11.1(6).
incomplete_type_declaration 3.10.1.
protected_declaration 9.4.
task_declaration 9.1.
generic_package_declaration 7.1.
generic_subprogram_declaration 6.1.
package_declaration 7.1.
subprogram_declaration 6.1.
declaration of a partial view 7.3.
declaration to which a pragma Elaborate_Body applies
10.2.1.
deferred constant declaration 7.4.
protected entry_declaration 9.5.2.
Reraise_Occurrence 11.4.1.
reserved interrupt C.3.
reserved word 2.9.
Reserved_128 A.3.3.
Reserved_129 A.3.3.
Reserved_132 A.3.3.
Reserved_153 A.3.3.
Reserved_Check
[partial] C.3.1.
Reset A.5.2(9), A.5.2(12), see A.5.2(9), A.5.2(12), see A.5.2(21),
A.5.2(24), see A.8.1(8), A.8.4(24), see A.8.1(8), A.8.4(8),
A.10.1(11), see A.12.1(11), see A.12.1(10).
resolution rules 1.1.2.
resolve
overload resolution 8.6.
Resource 9.4(27), see 9.4(27), see 9.4(28).
restriction 13.12.
used 13.12(3), see L(3), see L(32).
Restrictions
Immediate_Reclamation H.4.
Max_Asynchronous_Select_Nesting D.7.
Max_Protected_Entries D.7.
Max_Select_Alternatives D.7.
Max_Storage_At_Blocking D.7.
Max_Task_Entries D.7.
Max_Tasks D.7.
No_Abort_Statements D.7.
No_Access_Subprograms H.4.
No_Allocators H.4.
No_Asynchronous_Control D.7.
No_Delay H.4.
No_Dispatch H.4.
No_Dynamic_Priorities D.7.
No_Exceptions H.4.
No_Fixed_Point H.4.
No_Floating_Point H.4.
No_Implicit_Heap_Allocations D.7.
No_Local_Allocators H.4.
No_Nested_Finalization D.7.
No_Protected_Types H.4.
No_Recursion H.4.
No_Reentrancy H.4.
No_Task_Allocators D.7.
No_Task_Hierarchy D.7.
No_Terminate_Alternatives D.7.
No_Unchecked_Access H.4.
No_Unchecked_Conversion H.4.
No_Unchecked_Deallocation H.4.
No_IO H.4.
Restrictions pragma 13.12(3), see L(3), see L(32).
result interval
for a component of the result of evaluating
a complex function G.2.6.
for the evaluation of a predefined arithmetic
operation G.2.1.
for the evaluation of an elementary function G.2.4.
result subtype
of a function 6.5.
Result_Subtype A.5.2.
return expression 6.5.
return-by-reference type 6.5.
return_statement 6.5.
used 5.1(4), see P(4), see P(1).
Reverse_Solidus A.3.3.
Reviewable pragma H.3.1(3), see L(3), see L(33).
Rewind E.4.2(2), see E.4.2(2), see E.4.2(5).
RI A.3.3.
right curly bracket 2.1.
right parenthesis 2.1.
right square bracket 2.1.
Right_Angle_Quotation A.3.3.
Right_Curly_Bracket A.3.3.
Right_Indent 6.1.
Right_Parenthesis A.3.3.
Right_Square_Bracket A.3.3.
Roman 3.6.
Roman_Digit 3.5.2.
root library unit 10.1.1.
root type
of a class 3.4.1.
root_integer 3.5.4.
[partial] 3.4.1.
root_real 3.5.6.
[partial] 3.4.1.
Root_Storage_Pool 13.11.
Root_Stream_Type 13.13.1.
rooted at a type 3.4.1.
Rosso 8.5.4.
Rot 8.5.4.
rotate B.2.
Rotate_Left B.2.
Rotate_Right B.2.
Rouge 8.5.4.
Round attribute 3.5.10(12), see K(12), see K(203).
Rounding attribute A.5.3(36), see K(36), see K(207).
Row 12.1.
RPC
child of System E.5.
RPC-receiver E.5.
RPC_Receiver E.5.
RS A.3.3(6), see J.5(6), see J.5(4).
run-time check
See language-defined check 11.5.
run-time error 1.1.2(30), see 1.1.5(30), see 1.1.5(6),
11.5(2), 11.6(2), 11.6(1).
run-time polymorphism 3.9.2.
run-time semantics 1.1.2.
run-time type
See tag 3.9.
running a program
See program execution 10.2.
running task D.2.1.
ΓòÉΓòÉΓòÉ 49. index ΓòÉΓòÉΓòÉ
S'Adjacent A.5.3(49), see K(49), see K(10).
S'Ceiling A.5.3(34), see K(34), see K(29).
S'Class'Input 13.13.2(33), see K(33), see K(94).
S'Class'Output 13.13.2(30), see K(30), see K(167).
S'Class'Read 13.13.2(15), see K(15), see K(193).
S'Class'Write 13.13.2(12), see K(12), see K(284).
S'Compose A.5.3(25), see K(25), see K(40).
S'Copy_Sign A.5.3(52), see K(52), see K(46).
S'Exponent A.5.3(19), see K(19), see K(62).
S'Floor A.5.3(31), see K(31), see K(76).
S'Fraction A.5.3(22), see K(22), see K(82).
S'Input 13.13.2(23), see K(23), see K(98).
S'Leading_Part A.5.3(55), see K(55), see K(110).
S'Machine A.5.3(61), see K(61), see K(121).
S'Model A.5.3(69), see K(69), see K(153).
S'Output 13.13.2(20), see K(20), see K(171).
S'Read 13.13.2(7), see K(7), see K(197).
S'Remainder A.5.3(46), see K(46), see K(201).
S'Rounding A.5.3(37), see K(37), see K(209).
S'Scaling A.5.3(28), see K(28), see K(219).
S'Truncation A.5.3(43), see K(43), see K(250).
S'Unbiased_Rounding A.5.3(40), see K(40), see K(254).
S'Write 13.13.2(4), see K(4), see K(288).
safe range
of a floating point type 3.5.7(9), see 3.5.7(9), see 3.5.7(10).
Safe_First attribute A.5.3(71), see G.2.2(71), see G.2.2(5),
K.
Safe_Last attribute A.5.3(72), see G.2.2(72), see G.2.2(6),
K.
safety-critical systems H.
Salary 3.5.9.
Salary_Conversions B.4(108), see B.4(108), see B.4(120).
Salary_Type B.4(105), see B.4(105), see B.4(114).
Same_Denominator 7.2.
satisfies
a discriminant constraint 3.7.1.
a range constraint 3.5.
an index constraint 3.6.1.
for an access value 3.10.
Save A.5.2(12), see A.5.2(12), see A.5.2(24).
Save_Occurrence 11.4.1.
scalar type 3.2(3), see 3.5(1), see N(3), see 3.5(1), see N(37).
scalar_constraint 3.2.2.
used 3.2.2(5), see P(5), see P(1).
scale
of a decimal fixed point subtype 3.5.10,
K.
Scale attribute 3.5.10(11), see K(11), see K(215).
Scaling attribute A.5.3(27), see K(27), see K(217).
SCHAR_MAX B.3.
SCHAR_MIN B.3.
Schedule 3.6.
scope
informal definition 3.1.
of (a view of) an entity 8.2.
of a use_clause 8.4.
of a with_clause 10.1.2.
of a declaration 8.2.
Seconds 9.6.
Seconds_Count D.8.
Section_Sign A.3.3.
secure systems H.
Seize 9.4(27), see 9.4(28), see 9.5.2(27), see 9.4(28), see 9.5.2(33).
select an entry call
from an entry queue 9.5.3(13), see 9.5.3(13), see 9.5.3(16).
immediately 9.5.3.
select_alternative 9.7.1.
used 9.7.1(2), see P(2), see P(1).
select_statement 9.7.
used 5.1(5), see P(5), see P(1).
selected_component 4.1.3.
used 4.1(2), see P(2), see P(1).
selection
of an entry caller 9.5.2.
selective_accept 9.7.1.
used 9.7(2), see P(2), see P(1).
selector_name 4.1.3.
used 3.7.1(3), see 4.1.3(2), see 4.3.1(3), see 4.1.3(2), see 4.3.1(5),
6.4(5), 12.3(4), P(5), 12.3(4), P(1).
semantic dependence
of one compilation unit upon another 10.1.1.
semicolon 2.1(15), see A.3.3(15), see A.3.3(10).
separate compilation 10.1.
separator 2.2.
Sequence 4.6.
sequence of characters
of a string_literal 2.6.
sequence_of_statements 5.1.
used 5.3(2), 5.4(3), 5.5(2), 5.4(3), 5.5(2),
9.7.1(2), see 9.7.1(5), see 9.7.1(2), see 9.7.1(5), see 9.7.1(6),
9.7.2(3), see 9.7.3(2), see 9.7.4(3), see 9.7.3(2), see 9.7.4(3),
9.7.4(5), see 11.2(2), 11.2(5), see 11.2(2), 11.2(3),
P.
sequential
actions 9.10(11), see C.6(11), see C.6(17).
sequential access A.8.
sequential file A.8.
Sequential_IO J.1.
child of Ada A.8.1.
Server 9.1(23), see 9.7.1(23), see 9.7.1(24).
service
an entry queue 9.5.3.
Set 3.9.3(15), see 6.4(15), see 6.4(27),
D.12(9), D.12(9), D.12(10).
Set_Col A.10.1.
Set_Component 9.4(31), see 9.4(31), see 9.4(33).
Set_Error A.10.1.
Set_False D.10.
Set_Index A.8.4(14), see A.12.1(14), see A.12.1(22).
Set_Input A.10.1.
Set_Line A.10.1.
Set_Line_Length A.10.1.
Set_Mask 13.8(13), see 13.8(13), see 13.8(14).
Set_Mode A.12.1.
Set_Output A.10.1.
Set_Page_Length A.10.1.
Set_Priority D.5.
Set_True D.10.
Set_Value C.7.2.
Set_Im G.1.1.
Set_Re G.1.1.
Sets 3.9.3.
shared passive library unit E.2(4), see E.2.1(4), see E.2.1(4).
shared variable
protection of 9.10.
Shared_Array 9.4(31), see 9.4(31), see 9.4(32).
Shared_Passive pragma E.2.1(3), see L(3), see L(34).
Sharp J.5.
shift B.2.
Shift_Left B.2.
Shift_Right B.2.
Shift_Right_Arithmetic B.2.
Short 13.3(82), see B.3(82), see B.3(7).
short-circuit control form 4.5.1.
Short_Float 3.5.7.
Short_Integer 3.5.4.
Shut_Down 9.1.
SI A.3.3.
Sigma 12.1(24), see 12.2(24), see 12.2(12).
signal (an exception)
See raise 11.
signal
See interrupt C.3.
as defined between actions 9.10.
signal handling
example 9.7.4.
signed integer type 3.5.4.
signed_char B.3.
signed_integer_type_definition 3.5.4.
used 3.5.4(2), see P(2), see P(1).
Signed_Zeros attribute A.5.3(13), see K(13), see K(221).
simple entry call 9.5.3.
simple_expression 4.4.
used 3.5(3), see 3.5.4(3), 3.5.7(3), see 3.5.4(3), 3.5.7(3),
4.4(3), see 13.5.1(5), see 13.5.1(3), see 13.5.1(5), see 13.5.1(6),
P.
simple_statement 5.1.
used 5.1(3), see P(3), see P(1).
Sin A.5.1(5), see G.1.2(4)
single
class expected type 8.6.
single entry 9.5.2.
Single_Precision_Complex_Types B.5.
single_protected_declaration 9.4.
used 3.3.1(2), see P(2), see P(1).
single_task_declaration 9.1.
used 3.3.1(2), see P(2), see P(1).
Singular 11.1.
Sinh A.5.1(7), see G.1.2(7), see G.1.2(6).
size A.8.4(15), see A.12.1(15), see A.12.1(23).
of an object 13.1.
Size attribute 13.3(40), see 13.3(40), see 13.3(45),
K(223), K(223), K(228).
Size clause 13.3(7), see 13.3(41), see 13.3(7), see 13.3(41), see 13.3(48).
size_t B.3.
Skip_Line A.10.1.
Skip_Page A.10.1.
slice 4.1.2(2), see A.4.4(28), see A.4.5(2), see A.4.4(28), see A.4.5(22).
used 4.1(2), see P(2), see P(1).
small
of a fixed point type 3.5.9.
Small attribute 3.5.10(2), see K(2), see K(230).
Small clause 3.5.10(2), see 13.3(2), see 13.3(7).
Small_Int 3.2.2(15), see 3.5.4(15), see 3.5.4(35).
SO A.3.3(5), see J.5(5), see J.5(4).
Soft_Hyphen A.3.3.
SOH A.3.3.
solidus 2.1(15), see A.3.3(15), see A.3.3(8).
Source 13.9.
SPA A.3.3.
Space A.3.3(8), see A.4.1(8), see A.4.1(4).
space_character 2.1.
used 2.1(3), see P(3), see P(1).
special graphic character
a category of Character A.3.2.
special_character 2.1.
used 2.1(3), see P(3), see P(1).
names 2.1.
Special_Key 3.4.
Special_Set A.4.6.
Specialized Needs Annexes 1.1.2.
specifiable (of an attribute and for an entity) 13.3.
specifiable
of Address for entries J.7.1.
of Address for stand-alone objects and for program units
13.3.
of Alignment for first subtypes and objects 13.3.
of Bit_Order for record types and record extensions
13.5.3.
of Component_Size for array types 13.3.
of External_Tag for a tagged type 13.3(75), see K(75), see K(65).
of Input for a type 13.13.2.
of Machine_Radix for decimal first subtypes F.1.
of Output for a type 13.13.2.
of Read for a type 13.13.2.
of Size for first subtypes 13.3.
of Size for stand-alone objects 13.3.
of Small for fixed point types 3.5.10.
of Storage_Pool for a non-derived access-to-object type
13.11.
of Storage_Size for a task first subtype J.9.
of Storage_Size for a non-derived access-to-object type
13.11.
of Write for a type 13.13.2.
specific type 3.4.1.
specified (not!) 1.1.3.
specified
of an aspect of representation of an entity 13.1.
specified discriminant 3.7.
Spin 9.7.3(6)
Split 9.6(14), see D.8(14), see D.8(16).
Sqrt A.5.1(4), see B.1(4), see B.1(51), G.1.2(3)
Square 3.2.2(15), see 3.7(35), see 12.3(15), see 3.7(35), see 12.3(24).
Squaring 12.1(22), see 12.2(22), see 12.2(7).
SS2 A.3.3.
SS3 A.3.3.
SSA A.3.3.
ST A.3.3.
Stack 12.8(3), see 12.8(4), see 12.8(3), see 12.8(4), see 12.8(14).
Stack_Bool 12.8.
Stack_Int 12.8.
Stack_Real 12.8.
stand-alone constant 3.3.1.
corresponding to a formal object of mode in 12.4(10)
stand-alone object 3.3.1.
stand-alone variable 3.3.1.
Standard A.1.
standard error file A.10.
standard input file A.10.
standard mode 1.1.5.
standard output file A.10.
standard storage pool 13.11.
Standard_Error A.10.1(16), see A.10.1(16), see A.10.1(19).
Standard_Input A.10.1(16), see A.10.1(16), see A.10.1(19).
Standard_Output A.10.1(16), see A.10.1(16), see A.10.1(19).
State 3.8.1(24), see 13.5.1(24), see 13.5.1(26),
A.5.2(11), see A.5.2(11), see A.5.2(23).
State_Mask 13.5.1.
statement 5.1.
used 5.1(2), see P(2), see P(1).
statement_identifier 5.1.
used 5.1(7), see 5.5(2), see 5.6(2), see P(7), see 5.5(2), see 5.6(2), see P(1).
static 4.9.
constant 4.9.
constraint 4.9.
delta constraint 4.9.
digits constraint 4.9.
discrete_range 4.9.
discriminant constraint 4.9.
expression 4.9.
function 4.9.
index constraint 4.9.
range 4.9.
range constraint 4.9.
scalar subtype 4.9.
string subtype 4.9.
subtype 4.9(26), see 12.4(26), see 12.4(9).
static semantics 1.1.2.
statically
constrained 4.9.
denote 4.9.
statically compatible
for a constraint and a scalar subtype 4.9.1.
for a constraint and an access or composite subtype
4.9.1.
for two subtypes 4.9.1.
statically deeper 3.10.2(4), see 3.10.2(4), see 3.10.2(17).
statically determined tag 3.9.2.
[partial] 3.9.2(15), see 3.9.2(15), see 3.9.2(19).
statically matching
effect on subtype-specific aspects 13.1.
for constraints 4.9.1.
for ranges 4.9.1.
for subtypes 4.9.1.
required 3.9.2(10), see 3.10.2(27), see 4.6(10), see 3.10.2(27), see 4.6(12),
4.6(16), 6.3.1(16), 6.3.1(16), 6.3.1(16), 6.3.1(17),
6.3.1(23), see 7.3(13), 12.5.1(23), see 7.3(13), 12.5.1(14),
12.5.3(6), see 12.5.3(7), 12.5.4(6), see 12.5.3(7), 12.5.4(3),
12.7.
statically tagged 3.9.2.
Status_Error A.8.1(15), A.8.4(18), see A.10.1(15), A.8.4(18), see A.10.1(85),
A.12.1(26), see A.13(26), see A.13(4).
storage deallocation
unchecked 13.11.2.
storage element 13.3.
storage management
user-defined 13.11.
storage node E.
storage place
of a component 13.5.
storage place attributes
of a component 13.5.2.
storage pool 3.10.
storage pool element 13.11.
storage pool type 13.11.
Storage_Array 13.7.1.
Storage_Check 11.5.
[partial] 11.1(6), 13.3(6), 13.3(67),
13.11(17), see D.7(17), see D.7(15).
Storage_Count 13.7.1.
subtype in package System.Storage_Elements 13.7.1.
Storage_Element 13.7.1.
Storage_Elements
child of System 13.7.1.
Storage_Error A.1.
raised by failure of run-time check
4.8(14), 11.1(4), 11.1(14), 11.1(4), 11.1(6),
11.5(23), 13.3(67), see 13.11(23), 13.3(67), see 13.11(17),
13.11(18), see A.7(14), D.7(18), see A.7(14), D.7(15).
Storage_Offset 13.7.1.
Storage_Pool attribute 13.11(13), see K(13), see K(232).
Storage_Pool clause 13.3(7), see 13.11(7), see 13.11(15).
Storage_Pools
child of System 13.11.
Storage_Size 13.11.
Storage_Size attribute 13.3(60), see 13.11(60), see 13.11(14),
J.9(2), K(2), K(234),
K.
Storage_Size clause 13.3(7), see 13.11(7), see 13.11(15).
See also pragma Storage_Size 13.3.
Storage_Size pragma 13.3(63), see L(63), see L(35).
Storage_Unit 13.7.
named number in package System 13.7.
Storage_IO
child of Ada A.9.
Strcpy B.3(78), see B.3.2(78), see B.3.2(48).
stream 13.13(1), A.12.1(1), A.12.1(13),
A.12.2(4), see A.12.3(4), see A.12.3(4).
stream type 13.13.
Stream_Access A.12.1(4), see A.12.2(3), see A.12.3(4), see A.12.2(3), see A.12.3(3).
Stream_Element 13.13.1.
Stream_Element_Array 13.13.1.
Stream_Element_Count 13.13.1.
Stream_Element_Offset 13.13.1.
Stream_IO
child of Ada.Streams A.12.1.
Streams
child of Ada 13.13.1.
strict mode G.2.
String 3.6.3(4), see A.1(4), see A.1(37).
string type 3.6.3.
String_Access A.4.5.
string_element 2.6.
used 2.6(2), see P(2), see P(1).
string_literal 2.6.
used 4.4(7), see 6.1(9), see P(7), see 6.1(9), see P(1).
Strings
child of Ada A.4.1.
child of Interfaces.C B.3.1.
Strlen B.3.1.
structure
See record type 3.8.
STS A.3.3.
STX A.3.3(5), see J.5(5), see J.5(4).
SUB A.3.3(6), see J.5(6), see J.5(4).
subaggregate
of an array_aggregate 4.3.3.
subcomponent 3.2.
subprogram 6.
abstract 3.9.3.
subprogram call 6.4.
subprogram instance 12.3.
subprogram_body 6.3.
used 3.11(6), 9.4(6), 9.4(8),
10.1.1(7), see P(7), see P(1).
subprogram_body_stub 10.1.3.
used 10.1.3(2), see P(2), see P(1).
subprogram_declaration 6.1.
used 3.1(3), 9.4(5), see 9.4(3), 9.4(5), see 9.4(8),
10.1.1(5), see P(5), see P(1).
subprogram_default 12.6.
used 12.6(2), see P(2), see P(1).
subprogram_renaming_declaration 8.5.4.
used 8.5(2), see 10.1.1(6), see P(2), see 10.1.1(6), see P(1).
subprogram_specification 6.1.
used 6.1(2), 6.1(3), 6.3(2), 6.1(3), 6.3(2),
8.5.4(2), see 10.1.3(3), see 12.1(2), see 10.1.3(3), see 12.1(3),
12.6(2), P(2), P(1).
subsystem 10.1(3), see N(3), see N(22).
Subtraction 3.9.1.
subtype (of an object)
See actual subtype of an object 3.3(23), see 3.3.1(23), see 3.3.1(9).
subtype 3.2(8), see N(8), see N(38).
subtype conformance 6.3.1.
[partial] 3.10.2(34), see 9.5.4(34), see 9.5.4(17).
required 3.9.2(10), see 3.10.2(32), see 4.6(10), see 3.10.2(32), see 4.6(19),
8.5.4(5), 9.5.4(5), 13.3(5), 9.5.4(5), 13.3(6).
subtype conversion
See also implicit subtype conversion 4.6.
See type conversion 4.6.
subtype-specific
of a representation item 13.1.
of an aspect 13.1.
subtype_declaration 3.2.2.
used 3.1(3), see P(3), see P(1).
subtype_indication 3.2.2.
used 3.2.2(2), see 3.3.1(2), see 3.4(2), see 3.3.1(2), see 3.4(2),
3.6(6), 3.6(7), 3.6.1(6), 3.6(7), 3.6.1(3),
3.10(3), 4.8(2), 7.3(3), 4.8(2), 7.3(3),
P.
subtype_mark 3.2.2.
used 3.2.2(3), see 3.6(4), 3.7(3), see 3.6(4), 3.7(5),
3.10(6), 4.3.2(3), see 4.4(6), 4.3.2(3), see 4.4(3),
4.6(2), 4.7(2), 6.1(2), 4.7(2), 6.1(13),
6.1(15), 8.4(4), 8.5.1(15), 8.4(4), 8.5.1(2),
12.3(5), 12.4(2), 12.5.1(5), 12.4(2), 12.5.1(3),
P.
subtypes
of a profile 6.1.
subunit 10.1.3(7), see 10.1.3(7), see 10.1.3(8).
used 10.1.1(3), see P(3), see P(1).
Succ attribute 3.5(22), see K(22), see K(238).
Suit 3.5.1.
Sum 12.1(24), see 12.2(24), see 12.2(10).
super
See view conversion 4.6.
Superscript_One A.3.3.
Superscript_Three A.3.3.
Superscript_Two A.3.3.
Suppress pragma 11.5(4), see L(4), see L(36).
suppressed check 11.5.
Suspend_Until_True D.10.
Suspension_Object D.10.
Swap 12.3.
Switch 6.1.
SYN A.3.3(6), see J.5(6), see J.5(4).
synchronization 9.
Synchronous_Task_Control
child of Ada D.10.
syntactic category 1.1.4.
syntax
complete listing P.
cross reference P.
notation 1.1.4.
under Syntax heading 1.1.2.
System 13.7.
System.Address_To_Access_Conversions 13.7.2.
System.Machine_Code 13.8.
System.RPC E.5.
System.Storage_Elements 13.7.1.
System.Storage_Pools 13.11.
System_Name 13.7.
systems programming C.
ΓòÉΓòÉΓòÉ 50. index ΓòÉΓòÉΓòÉ
T 13.11.
Table 3.2.1(15), 3.6(28), see 12.5(15), 3.6(28), see 12.5(14),
12.5.3(11), see 12.8(5), see 12.8(11), see 12.8(5), see 12.8(14).
Tag 3.9.
Tag attribute 3.9(16), see 3.9(16), see 3.9(18),
K(242), K(242), K(244).
tag indeterminate 3.9.2.
tag of an object 3.9.
class-wide object 3.9.
object created by an allocator 3.9.
preserved by type conversion and parameter passing
3.9.
returned by a function 3.9(23), see 3.9(23), see 3.9(24).
stand-alone object, component, or aggregate 3.9.
Tag_Check 11.5.
[partial] 3.9.2(16), see 4.6(42), see 4.6(16), see 4.6(42), see 4.6(52),
5.2(10), 6.5(10), 6.5(9).
Tag_Error 3.9.
tagged type 3.9(2), see N(2), see N(39).
Tags
child of Ada 3.9.
tail (of a queue) D.2.1.
Tail A.4.3(37), see A.4.3(38), see A.4.4(37), see A.4.3(38), see A.4.4(72),
A.4.4(73), see A.4.5(67), see A.4.5(73), see A.4.5(67), see A.4.5(68).
Take 3.9.3.
Tan A.5.1(5), see G.1.2(5), see G.1.2(4).
Tanh A.5.1(7), see G.1.2(7), see G.1.2(6).
Tape E.4.2.
Tape_Client E.4.2.
Tape_Driver E.4.2(4), see E.4.2(4), see E.4.2(5).
Tape_Ptr E.4.2.
Tapes E.4.2.
target 13.9.
of an assignment_statement 5.2.
of an assignment operation 5.2.
target entry
of a requeue_statement 9.5.4.
target object
of a requeue_statement 9.5.
of a call on an entry or a protected subprogram 9.5.
target statement
of a goto_statement 5.8.
target subtype
of a type_conversion 4.6.
task 9.
activation 9.2.
completion 9.3.
dependence 9.3.
execution 9.2.
termination 9.3.
task declaration 9.1.
task dispatching D.2.1.
task dispatching point D.2.1.
[partial] D.2.1(8), see D.2.2(8), see D.2.2(12).
task dispatching policy D.2.2.
[partial] D.2.1.
task priority D.1.
task state
abnormal 9.8.
blocked 9.
callable 9.9.
held D.11.
inactive 9.
ready 9.
terminated 9.
Task type N.
task unit 9.
Task_Attributes
child of Ada C.7.2.
task_body 9.1.
used 3.11(6), see P(6), see P(1).
task_body_stub 10.1.3.
used 10.1.3(2), see P(2), see P(1).
task_definition 9.1.
used 9.1(2), see 9.1(3), see P(2), see 9.1(3), see P(1).
Task_Dispatching_Policy pragma D.2.2(2), see L(2), see L(37).
Task_Identification
child of Ada C.7.1.
task_item 9.1.
used 9.1(4), see P(4), see P(1).
task_type_declaration 9.1.
used 3.2.1(3), see P(3), see P(1).
Task_ID C.7.1.
Tasking_Error A.1.
raised by failure of run-time check
9.2(5), 9.5.3(21), 11.1(5), 9.5.3(21), 11.1(4),
13.11.2(13), see 13.11.2(14), see C.7.2(13), see 13.11.2(14), see C.7.2(13),
D.5(8), D.11(8), D.11(8).
template 12.
See generic unit 12.
for a formal package 12.7.
term 4.4.
used 4.4, P(1)
terminal interrupt
example 9.7.4.
terminate_alternative 9.7.1.
used 9.7.1(4), see P(4), see P(1).
terminated
a task state 9.
Terminated attribute 9.9(3), see K(3), see K(246).
termination
of a partition E.1.
Terminator_Error B.3.
Test B.3.
Test_Call B.4.
Test_External_Formats B.4.
Test_Pointers B.3.2.
tested type
of a membership test 4.5.2.
text of a program 2.2.
Text_Streams
child of Ada.Text_IO A.12.2(3), see A.12.3(3), see A.12.3(3).
Text_IO J.1.
child of Ada A.10.1.
throw (an exception)
See raise 11.
tick 2.1(15), see 13.7(10), see D.8(15), see 13.7(10), see D.8(7).
named number in package System 13.7.
Tilde A.3.3.
Time 9.6(10), see D.8(10), see D.8(4).
time base 9.6.
time limit
example 9.7.4.
time type 9.6.
Time-dependent Reset procedure
of the random number generator A.5.2.
time-out
See asynchronous_select 9.7.4.
See selective_accept 9.7.1.
See timed_entry_call 9.7.2.
example 9.7.4.
Time_Error 9.6.
Time_First D.8.
Time_Last D.8.
Time_Span D.8.
Time_Span_First D.8.
Time_Span_Last D.8.
Time_Span_Unit D.8.
Time_Span_Zero D.8.
Time_Unit D.8.
Time_Of 9.6(15), see D.8(15), see D.8(16).
timed_entry_call 9.7.2.
used 9.7(2), see P(2), see P(1).
timer interrupt
example 9.7.4.
times operator 4.4(1), see 4.5.5(1), see 4.5.5(1).
timing
See delay_statement 9.6.
TM 8.5.3.
To_Ada B.3(22), see B.3(26), see B.3(22), see B.3(26), see B.3(28),
B.3(32), see B.3(37), see B.3(32), see B.3(37), see B.3(39),
B.4(17), see B.4(19), see B.5(17), see B.4(19), see B.5(13),
B.5(14), see B.5(14), see B.5(16).
To_Address 13.7.1(10), see 13.7.2(10), see 13.7.2(3).
To_Basic A.3.2(6), see A.3.2(6), see A.3.2(7).
To_Binary B.4(45), see B.4(45), see B.4(48).
To_Bounded_String A.4.4.
To_Character A.3.2.
To_COBOL B.4(17), see B.4(17), see B.4(18).
To_Decimal B.4(35), see B.4(35), see B.4(40),
B.4(44), see B.4(44), see B.4(47).
To_Display B.4.
To_Domain A.4.2(24), see A.4.7(24)
To_Duration D.8.
To_Fortran B.5(13), see B.5(14), see B.5(13), see B.5(14), see B.5(15).
To_Integer 13.7.1.
To_ISO_646 A.3.2(11), see A.3.2(11), see A.3.2(12).
To_Long_Binary B.4.
To_Lower A.3.2(6), see A.3.2(6), see A.3.2(7).
To_Mapping A.4.2(23), see A.4.7(23), see A.4.7(23).
To_Packed B.4.
To_Picture F.3.3.
To_Pointer 13.7.2.
To_Range A.4.2(24), see A.4.7(24), see A.4.7(25).
To_Ranges A.4.2(10), see A.4.7(10), see A.4.7(10).
To_Sequence A.4.2(19), see A.4.7(19), see A.4.7(19).
To_Set A.4.2(8), A.4.2(9), see A.4.2(8), A.4.2(9), see A.4.2(17),
A.4.2(18), see A.4.7(8), see A.4.7(18), see A.4.7(8), see A.4.7(9),
A.4.7(17), see A.4.7(17), see A.4.7(18).
To_String A.3.2(16), see A.4.4(12), see A.4.5(16), see A.4.4(12), see A.4.5(11).
To_Time_Span D.8.
To_Unbounded_String A.4.5(9), see A.4.5(9), see A.4.5(10).
To_Upper A.3.2(6), see A.3.2(6), see A.3.2(7).
To_Wide_Character A.3.2.
To_Wide_String A.3.2.
To_C B.3(21), see B.3(25), see B.3(21), see B.3(25), see B.3(27),
B.3(32), see B.3(36), see B.3(32), see B.3(36), see B.3(38).
token
See lexical element 2.2.
Tolerance 3.3.1.
Trailing_Nonseparate B.4.
Trailing_Separate B.4.
transfer of control 5.1.
Translate A.4.3(18), see A.4.3(19), see A.4.3(18), see A.4.3(19), see A.4.3(20),
A.4.3(21), see A.4.4(53), see A.4.4(21), see A.4.4(53), see A.4.4(54),
A.4.4(55), see A.4.4(56), see A.4.5(55), see A.4.4(56), see A.4.5(48),
A.4.5(49), see A.4.5(50), see A.4.5(49), see A.4.5(50), see A.4.5(51).
Traverse_Tree 6.1.
triggering_alternative 9.7.4.
used 9.7.4(2), see P(2), see P(1).
triggering_statement 9.7.4.
used 9.7.4(3), see P(3), see P(1).
Trim A.4.3(31), see A.4.3(32), see A.4.3(31), see A.4.3(32), see A.4.3(33),
A.4.3(34), see A.4.4(67), see A.4.4(34), see A.4.4(67), see A.4.4(68),
A.4.4(69), see A.4.5(61), see A.4.5(69), see A.4.5(61), see A.4.5(62),
A.4.5(63), see A.4.5(63), see A.4.5(64).
Trim_End A.4.1.
True 3.5.3.
Truncation A.4.1.
Truncation attribute A.5.3(42), see K(42), see K(248).
two's complement
modular types 3.5.4.
Two_Pi 3.3.2.
type 3.2(1), see N(1), see N(41).
See also tag 3.9.
abstract 3.9.3.
See also language-defined types
type conformance 6.3.1.
[partial] 3.4(17), see 8.3(17), see 8.3(8),
8.3(26), see 10.1.4(26), see 10.1.4(4).
required 3.11.1(5), see 4.1.4(5), see 4.1.4(14),
8.6(26), 9.5.4(26), 9.5.4(3).
type conversion 4.6.
See also qualified_expression 4.7.
access 4.6(13), see 4.6(18), see 4.6(13), see 4.6(18), see 4.6(47).
arbitrary order 1.1.4.
array 4.6(9), see 4.6(9), see 4.6(36).
composite (non-array) 4.6(21), see 4.6(21), see 4.6(40).
enumeration 4.6(21), see 4.6(21), see 4.6(34).
numeric 4.6(8), see 4.6(8), see 4.6(29).
unchecked 13.9.
type conversion, implicit
See implicit subtype conversion 4.6.
type extension 3.9(2), see 3.9.1(2), see 3.9.1(1).
type of a discrete_range 3.6.1.
type of a range 3.5.
type parameter
See discriminant 3.7.
type profile
See profile, type conformant 6.3.1.
type resolution rules 8.6.
if any type in a specified class of types is expected
8.6.
if expected type is specific 8.6.
if expected type is universal or class-wide 8.6.
type tag
See tag 3.9.
type-related
aspect 13.1.
representation item 13.1.
type_conversion 4.6.
used 4.1(2), see P(2), see P(1).
See also unchecked type conversion 13.9.
type_declaration 3.2.1.
used 3.1(3), see P(3), see P(1).
type_definition 3.2.1.
used 3.2.1(3), see P(3), see P(1).
Type_Set A.10.1(7), see A.10.10(7), see A.10.10(3).
types
of a profile 6.1.
ΓòÉΓòÉΓòÉ 51. index ΓòÉΓòÉΓòÉ
UC_Icelandic_Eth A.3.3.
UC_Icelandic_Thorn A.3.3.
UC_A_Acute A.3.3.
UC_A_Circumflex A.3.3.
UC_A_Diaeresis A.3.3.
UC_A_Grave A.3.3.
UC_A_Ring A.3.3.
UC_A_Tilde A.3.3.
UC_AE_Diphthong A.3.3.
UC_C_Cedilla A.3.3.
UC_E_Acute A.3.3.
UC_E_Circumflex A.3.3.
UC_E_Diaeresis A.3.3.
UC_E_Grave A.3.3.
UC_I_Acute A.3.3.
UC_I_Circumflex A.3.3.
UC_I_Diaeresis A.3.3.
UC_I_Grave A.3.3.
UC_N_Tilde A.3.3.
UC_O_Acute A.3.3.
UC_O_Circumflex A.3.3.
UC_O_Diaeresis A.3.3.
UC_O_Grave A.3.3.
UC_O_Oblique_Stroke A.3.3.
UC_O_Tilde A.3.3.
UC_U_Acute A.3.3.
UC_U_Circumflex A.3.3.
UC_U_Diaeresis A.3.3.
UC_U_Grave A.3.3.
UC_Y_Acute A.3.3.
UCHAR_MAX B.3.
ultimate ancestor
of a type 3.4.1.
unary adding operator 4.5.4.
unary operator 4.5.
unary_adding_operator 4.5.
used 4.4(4), see P(4), see P(1).
Unbiased_Rounding attribute A.5.3(39), see K(39), see K(252).
Unbounded A.10.1.
child of Ada.Strings A.4.5.
Unbounded_String A.4.5.
unchecked storage deallocation 13.11.2.
unchecked type conversion 13.9.
Unchecked_Access attribute 13.10(3), see H.4(3), see H.4(18),
K.
See also Access attribute 3.10.2.
Unchecked_Conversion J.1.
child of Ada 13.9.
Unchecked_Deallocation J.1.
child of Ada 13.11.2.
unconstrained 3.2.
object 3.3.1(9), see 3.10(9), see 6.4.1(9), see 3.10(9), see 6.4.1(16).
subtype 3.2(9), 3.4(6), 3.5(9), 3.4(6), 3.5(7),
3.5.1(10), see 3.5.4(9), 3.5.4(10), see 3.5.4(9), 3.5.4(10),
3.5.7(11), see 3.5.9(13), see 3.5.9(11), see 3.5.9(13), see 3.5.9(16),
3.6(15), 3.6(16), 3.7(15), 3.6(16), 3.7(26),
3.9(15), 3.10(14), K(15), 3.10(14), K(33).
unconstrained_array_definition 3.6.
used 3.6(2), see P(2), see P(1).
undefined result 11.6.
underline 2.1(15), see J.5(15), see J.5(6).
used 2.3(2), 2.4.1(2), 2.4.1(3),
2.4.2(4), see P(4), see P(1).
Uniformly_Distributed A.5.2.
uninitialized allocator 4.8.
uninitialized variables 13.9.1.
[partial] 3.3.1.
Union 3.9.3.
unit consistency E.3.
Unit_Set 3.9.3.
universal type 3.4.1.
universal_fixed
[partial] 3.5.6.
universal_integer 3.5.4.
[partial] 3.5.4.
universal_real
[partial] 3.5.6.
unknown discriminants 3.7.
unknown_discriminant_part 3.7.
used 3.7(2), see P(2), see P(1).
unmarshalling E.4.
unpolluted 13.13.1.
unsigned B.3, B.4(23)
unsigned type
See modular type 3.5.4.
Unsigned_ B.2.
unsigned_char B.3.
unsigned_long B.3.
unsigned_short B.3.
unspecified 1.1.3.
[partial] 2.1(5), 4.5.2(13), see 4.5.5(5), 4.5.2(13), see 4.5.5(21),
6.2(11), 7.2(5), 9.8(11), 7.2(5), 9.8(14),
10.2(26), 11.1(6), 11.5(26), 11.1(6), 11.5(27),
13.1(18), 13.7.2(5), see 13.9.1(18), 13.7.2(5), see 13.9.1(7),
13.11(20), A.1(1), A.5.1(20), A.1(1), A.5.1(34),
A.5.2(28), A.5.2(34), see A.7(28), A.5.2(34), see A.7(6),
A.10(8), A.10.7(8), see A.10.7(8), A.10.7(8), see A.10.7(12),
A.10.7(19), see A.14(1), A.15(19), see A.14(1), A.15(20),
D.2.2(6), D.8(19), G.1.1(6), D.8(19), G.1.1(40),
G.1.2(33), G.1.2(48), see H(33), G.1.2(48), see H(4),
H.2.
Up_To_K 3.2.2.
update B.3.1(18), see B.3.1(18), see B.3.1(19).
the value of an object 3.3.
Update_Error B.3.1.
upper bound
of a range 3.5.
upper-case letter
a category of Character A.3.2.
upper_case_identifier_letter 2.1.
Upper_Case_Map A.4.6.
Upper_Set A.4.6.
US A.3.3.
usage name 3.1.
use-visible 8.3(4), see 8.4(4), see 8.4(9).
use_clause 8.4.
used 3.11(4), see 10.1.2(4), see 10.1.2(3),
12.1(5), see P(5), see P(1).
Use_Error A.8.1(15), A.8.4(18), see A.10.1(15), A.8.4(18), see A.10.1(85),
A.12.1(26), see A.13(26), see A.13(4).
use_package_clause 8.4.
used 8.4(2), see P(2), see P(1).
use_type_clause 8.4.
used 8.4(2), see P(2), see P(1).
User 9.1.
user-defined assignment 7.6.
user-defined heap management 13.11.
user-defined operator 6.6.
user-defined storage management 13.11.
ΓòÉΓòÉΓòÉ 52. index ΓòÉΓòÉΓòÉ
Val attribute 3.5.5(5), see K(5), see K(258).
Valid B.4(33), B.4(38), see B.4(33), B.4(38), see B.4(43),
F.3.3(5), see F.3.3(5), see F.3.3(12).
Valid attribute 13.9.2(3), see H(6), see K(3), see H(6), see K(262).
Value A.4.2(21), see A.5.2(14), see A.5.2(21), see A.5.2(14), see A.5.2(26),
B.3.1(13), see B.3.1(14), see B.3.1(13), see B.3.1(14), see B.3.1(15),
B.3.1(16), see B.3.2(6), B.3.2(16), see B.3.2(6), B.3.2(7),
C.7.2.
Value attribute 3.5(52), see K(52), see K(264).
value conversion 4.6.
Var_Line 3.6.1.
variable 3.3.
variable object 3.3.
variable view 3.3.
variant 3.8.1.
used 3.8.1(2), see P(2), see P(1).
See also tagged type 3.9.
variant_part 3.8.1.
used 3.8(4), see P(4), see P(1).
Vector 3.6(26), see 12.1(24), see 12.5.3(26), see 12.1(24), see 12.5.3(11).
version
of a compilation unit E.3.
Version attribute E.3(3), see K(3), see K(268).
vertical line 2.1.
Vertical_Line A.3.3.
view 3.1(7), see N(12), see N(7), see N(12), see N(42).
view conversion 4.6.
virtual function
See dispatching subprogram 3.9.2.
Virtual_Length B.3.2.
visibility
direct 8.3(2), see 8.3(2), see 8.3(21).
immediate 8.3(4), see 8.3(4), see 8.3(21).
use clause 8.3(4), see 8.4(4), see 8.4(9).
visibility rules 8.3.
visible 8.3(2), see 8.3(2), see 8.3(14).
within a pragma in a context_clause 10.1.6.
within a pragma that appears at the place of a compilation unit
10.1.6.
within a with_clause 10.1.6.
within a use_clause in a context_clause 10.1.6.
within the parent_unit_name of a library unit 10.1.6.
within the parent_unit_name of a subunit 10.1.6.
visible part 8.2.
of a formal package 12.7.
of a generic unit 8.2.
of a package (other than a generic formal package)
7.1.
of a protected unit 9.4.
of a task unit 9.1.
of a view of a callable entity 8.2.
of a view of a composite type 8.2.
volatile C.6.
Volatile pragma C.6(4), see L(4), see L(38).
Volatile_Components pragma C.6(6), see L(6), see L(39).
Volt 3.5.9.
VT A.3.3.
VTS A.3.3.
ΓòÉΓòÉΓòÉ 53. index ΓòÉΓòÉΓòÉ
wchar_t B.3.
Weekday 3.5.1.
well-formed picture String
for edited output F.3.1.
Wide_Bounded
child of Ada.Strings A.4.7.
Wide_Character 3.5.2(3), see A.1(3), see A.1(36).
Wide_Character_Mapping A.4.7.
Wide_Character_Mapping_Function A.4.7.
Wide_Character_Range A.4.7.
Wide_Character_Sequence A.4.7.
Wide_Character_Set A.4.7.
Wide_Constants
child of Ada.Strings.Wide_Maps A.4.7.
Wide_Fixed
child of Ada.Strings A.4.7.
Wide_Image attribute 3.5(28), see K(28), see K(270).
Wide_Maps
child of Ada.Strings A.4.7.
wide_nul B.3.
Wide_Space A.4.1.
Wide_String 3.6.3(4), see A.1(4), see A.1(41).
Wide_Text_IO
child of Ada A.11.
Wide_Unbounded
child of Ada.Strings A.4.7.
Wide_Value attribute 3.5(40), see K(40), see K(274).
Wide_Width attribute 3.5(38), see K(38), see K(278).
Width attribute 3.5(39), see K(39), see K(280).
with_clause 10.1.2.
used 10.1.2(3), see P(3), see P(1).
mentioned in 10.1.2(6)
within
immediately 8.1.
word 13.3(8), see 13.5.1(8), see 13.5.1(25).
Word_Size 13.7.
named number in package System 13.7.
Worker A.5.2.
Write 7.5(19), 7.5(20), 9.1(19), 7.5(20), 9.1(24),
9.11(8), 9.11(9), 13.13.1(8), 9.11(9), 13.13.1(6),
A.8.1(12), A.8.4(13), A.9(12), A.8.4(13), A.9(7),
A.12.1(18), see A.12.1(19), see E.5(18), see A.12.1(19), see E.5(8).
Write attribute 13.13.2(3), see 13.13.2(3), see 13.13.2(11),
K(282), K(282), K(286).
Write clause 13.3(7), see 13.13.2(7), see 13.13.2.
ΓòÉΓòÉΓòÉ 54. index ΓòÉΓòÉΓòÉ
xor operator 4.4(1), see 4.5.1(1), see 4.5.1(2).
ΓòÉΓòÉΓòÉ 55. index ΓòÉΓòÉΓòÉ
Year 9.6.
Year_Number 9.6.
Yen_Sign A.3.3.
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