Copyright ©1995 by NeXT Computer, Inc.  All Rights Reserved.

Defined Types


DECLARED IN objc/objc.h

SYNOPSIS    typedef char BOOL;

DESCRIPTION This type carries the basic boolean distinction between YES and NO (true and false).


DECLARED IN objc/objc.h

SYNOPSIS    typedef struct objc_class *Class;

DESCRIPTION Class is the data type for class objects.  The objc_class structure it refers to holds information compiled from the class definition; details of its contents can be found in Chapter 15, "Run-Time System."

Every object has an isa instance variable of this type, which enables the object to identify its class.

Class objects can also be assigned to type id.  But just as instances of a class can be statically typed by using the class name, class objects can be more particularly typed with the Class data type.


DECLARED IN objc/objc.h

SYNOPSIS    typedef struct objc_object {
Class isa;
} *id;

DESCRIPTION The id data type designates an Objective C object of any class.  All objects, including both instances and class objects, can be assigned to this type.


DECLARED IN objc/objc.h

SYNOPSIS    typedef id (*IMP) (id, SEL, ...);

DESCRIPTION This is the data type returned by Object's methodFor: method to identify a method implementation.  It's defined as a pointer to a function that returns an id and takes an object (self) and a selector (_cmd) as its first two arguments.


DECLARED IN objc/objc.h

SYNOPSIS    typedef struct objc_selector *SEL;

DESCRIPTION The SEL type identifies method selectors.  Valid SEL values are assigned only by the run-time system.  They are never 0.


DECLARED IN objc/objc.h

SYNOPSIS    typedef char *STR;

DESCRIPTION This type is a rarely used shorthand for a character string.  It's mainly of historical interest.

Symbolic Constants

Boolean Constants

DECLARED IN objc/objc.h


DESCRIPTION YES and NO are the standard values assigned to BOOL variables.

Empty Objects

DECLARED IN objc/objc.h

SYNOPSIS    nil (id)0
Nil (Class)0

DESCRIPTION nil is the common notation for a NULL object.  Nil is sometimes used for a NULL class object, but nil typically serves this purpose as well.