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Object-Oriented Programming
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Here are the commands for formatting descriptions about abstract
objects, such as are used in object-oriented programming. A class is a
defined type of abstract object. An instance of a class is a
particular object that has the type of the class. An instance variable
is a variable that belongs to the class but for which each instance has
its own value.
In a definition, if the name of a class is truly a name defined in
the programming system for a class, then you should write an `@code'
around it. Otherwise, it is printed in the usual text font.
`@defcv CATEGORY CLASS NAME'
The `@defcv' command is the general definition command for
variables associated with classes in object-oriented programming.
The `@defcv' command is followed by three arguments: the category
of thing being defined, the class to which it belongs, and its
name. Thus,
@defcv {Class Option} Window border-pattern
...
@end defcv
illustrates how you would write the first line of a definition of
the `border-pattern' class option of the class `Window'.
The template is
@defcv CATEGORY CLASS NAME
...
@end defcv
`@defcv' creates an entry in the index of variables.
`@defivar CLASS NAME'
The `@defivar' command is the definition command for instance
variables in object-oriented programming. `@defivar' is
equivalent to `@defcv {Instance Variable} ...'
The template is:
@defivar CLASS INSTANCE-VARIABLE-NAME
BODY-OF-DEFINITION
@end defivar
`@defivar' creates an entry in the index of variables.
`@defop CATEGORY CLASS NAME ARGUMENTS...'
The `@defop' command is the general definition command for
entities that may resemble methods in object-oriented programming.
These entities take arguments, as functions do, but are associated
with particular classes of objects.
For example, some systems have constructs called "wrappers" that
are associated with classes as methods are, but that act more like
macros than like functions. You could use `@defop Wrapper' to
describe one of these.
Sometimes it is useful to distinguish methods and "operations".
You can think of an operation as the specification for a method.
Thus, a window system might specify that all window classes have a
method named `expose'; we would say that this window system
defines an `expose' operation on windows in general. Typically,
the operation has a name and also specifies the pattern of
arguments; all methods that implement the operation must accept
the same arguments, since applications that use the operation do
so without knowing which method will implement it.
Often it makes more sense to document operations than methods. For
example, window application developers need to know about the
`expose' operation, but need not be concerned with whether a given
class of windows has its own method to implement this operation.
To describe this operation, you would write:
@defop Operation windows expose
The `@defop' command is written at the beginning of a line and is
followed on the same line by the overall name of the category of
operation, the name of the class of the operation, the name of the
operation, and its arguments, if any.
The template is:
@defop CATEGORY CLASS NAME ARGUMENTS...
BODY-OF-DEFINITION
@end defop
`@defop' creates an entry, such as ``expose' on `windows'', in the
index of functions.
`@defmethod CLASS NAME ARGUMENTS...'
The `@defmethod' command is the definition command for methods in
object-oriented programming. A method is a kind of function that
implements an operation for a particular class of objects and its
subclasses. In the Lisp Machine, methods actually were functions,
but they were usually defined with `defmethod'.
`@defmethod' is equivalent to `@defop Method ...'. The command is
written at the beginning of a line and is followed by the name of
the class of the method, the name of the method, and its
arguments, if any.
For example,
@defmethod `bar-class' bar-method argument
...
@end defmethod
illustrates the definition for a method called `bar-method' of the
class `bar-class'. The method takes an argument.
The template is:
@defmethod CLASS METHOD-NAME ARGUMENTS...
BODY-OF-DEFINITION
@end defmethod
`@defmethod' creates an entry in the index of functions, such as
``bar-method' on `bar-class''.