libobjc/objc/objc.h

   1 /* Basic data types for Objective C.
   2    Copyright (C) 1993-2023 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 3, or (at your option)
   9 any later version.
  10
  11 GCC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 Under Section 7 of GPL version 3, you are granted additional
  17 permissions described in the GCC Runtime Library Exception, version
  18 3.1, as published by the Free Software Foundation.
  19
  20 You should have received a copy of the GNU General Public License and
  21 a copy of the GCC Runtime Library Exception along with this program;
  22 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 <http://www.gnu.org/licenses/>.  */
  24
  25 #ifndef __objc_INCLUDE_GNU
  26 #define __objc_INCLUDE_GNU
  27
  28 /* This file contains the definition of the basic types used by the
  29    Objective-C language.  It needs to be included to do almost
  30    anything with Objective-C.  */
  31
  32 #ifdef __cplusplus
  33 extern "C" {
  34 #endif
  35
  36 #include <stddef.h>
  37
  38 /* The current version of the GNU Objective-C Runtime library in
  39    compressed ISO date format.  This should be updated any time a new
  40    version is released with changes to the public API (there is no
  41    need to update it if there were no API changes since the previous
  42    release).  This macro is only defined starting with the GNU
  43    Objective-C Runtime shipped with GCC 4.6.0.  If it is not defined,
  44    it is either an older version of the runtime, or another runtime.  */
  45 #define __GNU_LIBOBJC__ 20110608
  46
  47 /* Definition of the boolean type.
  48
  49    Compatibility note: the Apple/NeXT runtime defines a BOOL as a
  50    'signed char'.  The GNU runtime uses an 'unsigned char'.
  51
  52    Important: this could change and we could switch to 'typedef bool
  53    BOOL' in the future.  Do not depend on the type of BOOL.  */
  54 #undef BOOL
  55 typedef unsigned char  BOOL;
  56
  57 #define YES   (BOOL)1
  58 #define NO    (BOOL)0
  59
  60 /* The basic Objective-C types (SEL, Class, id) are defined as pointer
  61    to opaque structures.  The details of the structures are private to
  62    the runtime and may potentially change from one version to the
  63    other.  */
  64
  65 /* A SEL (selector) represents an abstract method (in the
  66    object-oriented sense) and includes all the details of how to
  67    invoke the method (which means its name, arguments and return
  68    types) but provides no implementation of its own.  You can check
  69    whether a class implements a selector or not, and if you have a
  70    selector and know that the class implements it, you can use it to
  71    call the method for an object in the class.  */
  72 typedef const struct objc_selector *SEL;
  73
  74 /* A Class is a class (in the object-oriented sense).  In Objective-C
  75    there is the complication that each Class is an object itself, and
  76    so belongs to a class too.  This class that a class belongs to is
  77    called its 'meta class'.  */
  78 typedef struct objc_class *Class;
  79
  80 /* An 'id' is an object of an unknown class.  The way the object data
  81    is stored inside the object is private and what you see here is
  82    only the beginning of the actual struct.  The first field is always
  83    a pointer to the Class that the object belongs to.  */
  84 typedef struct objc_object
  85 {
  86   /* 'class_pointer' is the Class that the object belongs to.  In case
  87      of a Class object, this pointer points to the meta class.
  88
  89      Compatibility Note: The Apple/NeXT runtime calls this field
  90      'isa'.  To access this field, use object_getClass() from
  91      runtime.h, which is an inline function so does not add any
  92      overhead and is also portable to other runtimes.  */
  93   Class class_pointer;
  94 } *id;
  95
  96 /* 'IMP' is a C function that implements a method.  When retrieving
  97    the implementation of a method from the runtime, this is the type
  98    of the pointer returned.  The idea of the definition of IMP is to
  99    represent a 'pointer to a general function taking an id, a SEL,
 100    followed by other unspecified arguments'.  You must always cast an
 101    IMP to a pointer to a function taking the appropriate, specific
 102    types for that function, before calling it - to make sure the
 103    appropriate arguments are passed to it.  The code generated by the
 104    compiler to perform method calls automatically does this cast
 105    inside method calls.  */
 106 typedef id (*IMP)(id, SEL, ...);
 107
 108 /* 'nil' is the null object.  Messages to nil do nothing and always
 109    return 0.  */
 110 #define nil (id)0
 111
 112 /* 'Nil' is the null class.  Since classes are objects too, this is
 113    actually the same object as 'nil' (and behaves in the same way),
 114    but it has a type of Class, so it is good to use it instead of
 115    'nil' if you are comparing a Class object to nil as it enables the
 116    compiler to do some type-checking.  */
 117 #define Nil (Class)0
 118
 119 /* TODO: Move the 'Protocol' declaration into objc/runtime.h.  A
 120    Protocol is simply an object, not a basic Objective-C type.  The
 121    Apple runtime defines Protocol in objc/runtime.h too, so it's good
 122    to move it there for API compatibility.  */
 123
 124 /* A 'Protocol' is a formally defined list of selectors (normally
 125    created using the @protocol Objective-C syntax).  It is mostly used
 126    at compile-time to check that classes implement all the methods
 127    that they are supposed to.  Protocols are also available in the
 128    runtime system as Protocol objects.  */
 129 #ifndef __OBJC__
 130   /* Once we stop including the deprecated struct_objc_protocol.h
 131      there is no reason to even define a 'struct objc_protocol'.  As
 132      all the structure details will be hidden, a Protocol basically is
 133      simply an object (as it should be).  */
 134   typedef struct objc_object Protocol;
 135 #else /* __OBJC__ */
 136   @class Protocol;
 137 #endif
 138
 139 /* Compatibility note: the Apple/NeXT runtime defines sel_getName(),
 140    sel_registerName(), object_getClassName(), object_getIndexedIvars()
 141    in this file while the GNU runtime defines them in runtime.h.
 142
 143    The reason the GNU runtime does not define them here is that they
 144    are not basic Objective-C types (defined in this file), but are
 145    part of the runtime API (defined in runtime.h).  */
 146
 147 #ifdef __cplusplus
 148 }
 149 #endif
 150
 151 #endif /* not __objc_INCLUDE_GNU */