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3d0d8739 | 1 | /* GNU Objective C Runtime messaging declarations |
5624e564 | 2 | Copyright (C) 1993-2015 Free Software Foundation, Inc. |
3d0d8739 NP |
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_message_INCLUDE_GNU | |
26 | #define __objc_message_INCLUDE_GNU | |
27 | ||
5b8b526e NP |
28 | #include "objc.h" |
29 | #include "objc-decls.h" | |
30 | ||
3d0d8739 NP |
31 | #ifdef __cplusplus |
32 | extern "C" { | |
33 | #endif | |
34 | ||
6176c2a9 | 35 | /* This file includes declarations of the messaging functions and |
db1792ee | 36 | types. */ |
6176c2a9 NP |
37 | |
38 | /* Compatibility note: the messaging function is one area where the | |
39 | GNU runtime and the Apple/NeXT runtime differ significantly. If | |
40 | you can, it is recommended that you use higher-level facilities | |
41 | (provided by a Foundation library such as GNUstep Base) to perform | |
db1792ee NP |
42 | forwarding or other advanced messaging tricks. */ |
43 | ||
44 | /* This function returns the IMP (C function implementing a method) to | |
45 | use to invoke the method with selector 'op' of receiver 'receiver'. | |
46 | ||
47 | This is the function used by the compiler when compiling method | |
48 | invocations with the GNU runtime. For example, the method call | |
49 | ||
50 | result = [receiver method]; | |
51 | ||
52 | is compiled by the compiler (with the GNU runtime) into the | |
53 | equivalent of: | |
54 | ||
55 | { | |
56 | IMP function = objc_msg_lookup (receiver, @selector (method)); | |
57 | result = function (receiver, @selector (method)); | |
58 | } | |
59 | ||
60 | so, a call to objc_msg_lookup() determines the IMP (the C function | |
61 | implementing the method) to call. Then, the function is called. | |
62 | If the method takes or returns different arguments, the compiler | |
63 | will cast 'function' to the right type before invoking it, making | |
64 | sure arguments and return value are handled correctly. | |
65 | ||
66 | objc_msg_lookup() must always return a valid function that can be | |
67 | called with the required method signature (otherwise the | |
68 | compiler-generated code shown above could segfault). If 'receiver' | |
69 | is NULL, objc_msg_lookup() returns a C function that does nothing, | |
70 | ignores all its arguments, and returns NULL (see nil_method.c). If | |
71 | 'receiver' does not respond to the selector 'op', objc_msg_lookup() | |
72 | will try to call +resolveClassMethod: or resolveInstanceMethod: as | |
73 | appropriate, and if they return YES, it will try the lookup again | |
74 | (+resolveClassMethod: and +resolveInstanceMethod: can thus install | |
75 | dynamically methods as they are requested). If | |
76 | +resolveClassMethod: or +resolveInstanceMethod: are either not | |
77 | available, or return NO, or return YES but 'receiver' still doesn't | |
78 | implement the 'selector' after calling them, the runtime returns a | |
79 | generic "forwarding" function that can be called with the required | |
80 | method signature and which can process the method invocation | |
81 | according to the forwarding API. There are two runtime hooks that | |
82 | allow Foundation libraries (such as GNUstep-Base) to return their | |
83 | own forwarding function in preference to the runtime ones. When | |
84 | that happens, the Foundation library effectively takes complete | |
85 | control of the forwarding process; any method invocation where the | |
86 | selector is not implemented by the receiver will end up calling a | |
87 | forwarding function chosen by the Foundation library. */ | |
88 | objc_EXPORT IMP objc_msg_lookup (id receiver, SEL op); | |
89 | ||
90 | /* Structure used when a message is send to a class's super class. | |
91 | The compiler generates one of these structures and passes it to | |
92 | objc_msg_lookup_super() when a [super method] call is compiled. */ | |
53f672ca | 93 | |
53f672ca NP |
94 | /* Modern API. */ |
95 | struct objc_super | |
96 | { | |
97 | id self; /* The receiver of the message. */ | |
98 | Class super_class; /* The superclass of the receiver. */ | |
99 | }; | |
6176c2a9 | 100 | |
db1792ee NP |
101 | /* This is used by the compiler instead of objc_msg_lookup () when |
102 | compiling a call to 'super', such as [super method]. This requires | |
103 | sending a message to super->self, but looking up the method as if | |
104 | super->self was in class super->super_class. */ | |
53f672ca | 105 | objc_EXPORT IMP objc_msg_lookup_super (struct objc_super *super, SEL sel); |
6176c2a9 | 106 | |
db1792ee NP |
107 | /* Hooks for method forwarding. They make it easy to substitute the |
108 | built-in forwarding with one based on a library, such as ffi, that | |
109 | implement closures, thereby avoiding gcc's __builtin_apply | |
110 | problems. __objc_msg_forward2's result will be preferred over that | |
ecfc2705 | 111 | of __objc_msg_forward if both are set and return non-NULL. */ |
6176c2a9 NP |
112 | objc_EXPORT IMP (*__objc_msg_forward)(SEL); |
113 | objc_EXPORT IMP (*__objc_msg_forward2)(id, SEL); | |
3d0d8739 NP |
114 | |
115 | #ifdef __cplusplus | |
116 | } | |
117 | #endif | |
118 | ||
119 | #endif /* not __objc_message_INCLUDE_GNU */ |