Appendix B

Reference Manual for the Objective-C Language

This appendix presents a formal grammar for the Objective-C extensions to the C language--as the Objective-C language is implemented for the OPENSTEP development environment. It adds to the grammar for ANSI standard C found in Appendix A of The C Programming Language (second edition, 1988) by Brian W. Kernighan and Dennis M. Ritchie, published by Prentice Hall, and should be read in conjunction with that book.

The Objective-C extensions introduce some new symbols (such as class-interface), but also make use of symbols (such as function-definition) that are explained in the standard C grammar. The symbols mentioned but not explained here are listed below:

Undefined Symbols

compound statement constant declaration declaration-list enum-specifier expression function-definition identifier parameter-type-list string struct-declaration-list struct-or-union typedef-name type-name

Of these, identifier and string are undefined terminal symbols. Objective-C adds no undefined terminal symbols of its own.

Two notational conventions used here differ from those used in The C Programming Language:

Literal symbols are shown in bold type.
Brackets enclose optional elements and are in italic type. Literal brackets, like other literal symbols, are non-italic and bold.

Otherwise, this appendix follows the conventions of the C reference manual. Each part of the grammar consists of a symbol followed by a colon and an indented list of mutually-exclusive possibilities for expanding the symbol. For example:

receiver:
expression
class-name
super

However, there is an exception: Even though they're not mutually exclusive, the constituents of classes, categories, and protocols are listed on separate lines to clearly show the ordering of elements. For example:

protocol-declaration:
@protocol protocol-name
[ protocol-reference-list ]
[ interface-declaration-list ]
@end

This exception to the general rule is easily recognized since each list terminates with @end.

There are just four entry points where the Objective-C language modifies the rules defined for standard C:

External declarations
Type specifiers
Type qualifiers
Primary expressions

This appendix is therefore divided into four sections corresponding to these points. Where a rule in the standard C grammar is modified by an Objective-C extension, the entire rule is repeated in its modified form.

EXTERNAL DECLARATIONS

external-declaration:
function-definition
declaration
class-interface
class-implementation
category-interface
category-implementation
protocol-declaration
class-declaration-list

class-interface:
@interface class-name [ : superclass-name ]
[ protocol-reference-list ]
[ instance-variables ]
[ interface-declaration-list ]
@end

class-implementation:
@implementation class-name [ : superclass-name ]
[ instance-variables ]
[ implementation-definition-list ]
@end

category-interface:
@interface class-name ( category-name )
[ protocol-reference-list ]
[ interface-declaration-list ]
@end

category-implementation:
@implementation class-name ( category-name )
[ implementation-definition-list ]
@end

protocol-declaration:
@protocol protocol-name
[ protocol-reference-list ]
[ interface-declaration-list ]
@end

class-declaration-list:
@class class-list ;

class-list:
class-name
class-list , class-name

protocol-reference-list:
< protocol-list >

protocol-list:
protocol-name
protocol-list , protocol-name

class-name:
identifier

superclass-name:
identifier

category-name:
identifier

protocol-name:
identifier

instance-variables:
{ [ visibility-specification ] struct-declaration-list [ instance-variables ] }

visibility-specification:
@private
@protected
@public

interface-declaration-list:
declaration
method-declaration
interface-declaration-list declaration
interface-declaration-list method-declaration

method-declaration:
class-method-declaration
instance-method-declaration

class-method-declaration:
+ [ method-type ] method-selector ;

instance-method-declaration:
- [ method-type ] method-selector ;

implementation-definition-list:
function-definition
declaration
method-definition
implementation-definition-list function-definition
implementation-definition-list declaration
implementation-definition-list method-definition

method-definition:
class-method-definition
instance-method-definition

class-method-definition:
+ [ method-type ] method-selector [ declaration-list ] compound-statement

instance-method-definition:
- [ method-type ] method-selector [ declaration-list ] compound-statement

method-selector:
unary-selector
keyword-selector [ , ... ]
keyword-selector [ , parameter-type-list ]

unary-selector:
selector

keyword-selector:
keyword-declarator
keyword-selector keyword-declarator

keyword-declarator:
: [ method-type ] identifier
selector : [ method-type ] identifier

selector:
identifier

method-type:
( type-name )

TYPE SPECIFIERS

type-specifier:
void
char
short
int
long
float
double
signed
unsigned
id [ protocol-reference-list ]
class-name [ protocol-reference-list ]
struct-or-union-specifier
enum-specifier
typedef-name

struct-or-union-specifier:
struct-or-union [ identifier ] { struct-declaration-list }
struct-or-union [ identifier ] { @defs ( class-name ) }
struct-or-union identifier

TYPE QUALIFIERS

type-qualifier:
const
volatile
protocol-qualifier

protocol-qualifier:
in
out
inout
bycopy
byref
oneway

PRIMARY EXPRESSIONS

primary-expression:
identifier
constant
string
( expression )
self
message-expression
selector-expression
protocol-expression
encode-expression

message-expression:
[ receiver message-selector ]

receiver:
expression
class-name
super

message-selector:
selector
keyword-argument-list

keyword-argument-list:
keyword-argument
keyword-argument-list keyword-argument

keyword-argument:
selector : expression
: expression

selector-expression:
@selector ( selector-name )

selector-name:
selector
keyword-name-list

keyword-name-list:
keyword-name
keyword-name-list keyword-name

keyword-name:
selector :
:

protocol-expression:
@protocol ( protocol-name )

encode-expression:
@encode ( type-name )