Object-Oriented Programming

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, such as `bar-method on bar-class', in the index of functions.