1*e4b17023SJohn Marino /* GNU Objective C Runtime messaging declarations 2*e4b17023SJohn Marino Copyright (C) 1993, 1995, 1996, 2004, 2009, 3*e4b17023SJohn Marino 2010 Free Software Foundation, Inc. 4*e4b17023SJohn Marino 5*e4b17023SJohn Marino This file is part of GCC. 6*e4b17023SJohn Marino 7*e4b17023SJohn Marino GCC is free software; you can redistribute it and/or modify 8*e4b17023SJohn Marino it under the terms of the GNU General Public License as published by 9*e4b17023SJohn Marino the Free Software Foundation; either version 3, or (at your option) 10*e4b17023SJohn Marino any later version. 11*e4b17023SJohn Marino 12*e4b17023SJohn Marino GCC is distributed in the hope that it will be useful, 13*e4b17023SJohn Marino but WITHOUT ANY WARRANTY; without even the implied warranty of 14*e4b17023SJohn Marino MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15*e4b17023SJohn Marino GNU General Public License for more details. 16*e4b17023SJohn Marino 17*e4b17023SJohn Marino Under Section 7 of GPL version 3, you are granted additional 18*e4b17023SJohn Marino permissions described in the GCC Runtime Library Exception, version 19*e4b17023SJohn Marino 3.1, as published by the Free Software Foundation. 20*e4b17023SJohn Marino 21*e4b17023SJohn Marino You should have received a copy of the GNU General Public License and 22*e4b17023SJohn Marino a copy of the GCC Runtime Library Exception along with this program; 23*e4b17023SJohn Marino see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 24*e4b17023SJohn Marino <http://www.gnu.org/licenses/>. */ 25*e4b17023SJohn Marino 26*e4b17023SJohn Marino #ifndef __objc_message_INCLUDE_GNU 27*e4b17023SJohn Marino #define __objc_message_INCLUDE_GNU 28*e4b17023SJohn Marino 29*e4b17023SJohn Marino #include "objc.h" 30*e4b17023SJohn Marino #include "objc-decls.h" 31*e4b17023SJohn Marino 32*e4b17023SJohn Marino #ifdef __cplusplus 33*e4b17023SJohn Marino extern "C" { 34*e4b17023SJohn Marino #endif 35*e4b17023SJohn Marino 36*e4b17023SJohn Marino /* This file includes declarations of the messaging functions and 37*e4b17023SJohn Marino types. */ 38*e4b17023SJohn Marino 39*e4b17023SJohn Marino /* Compatibility note: the messaging function is one area where the 40*e4b17023SJohn Marino GNU runtime and the Apple/NeXT runtime differ significantly. If 41*e4b17023SJohn Marino you can, it is recommended that you use higher-level facilities 42*e4b17023SJohn Marino (provided by a Foundation library such as GNUstep Base) to perform 43*e4b17023SJohn Marino forwarding or other advanced messaging tricks. */ 44*e4b17023SJohn Marino 45*e4b17023SJohn Marino /* This function returns the IMP (C function implementing a method) to 46*e4b17023SJohn Marino use to invoke the method with selector 'op' of receiver 'receiver'. 47*e4b17023SJohn Marino 48*e4b17023SJohn Marino This is the function used by the compiler when compiling method 49*e4b17023SJohn Marino invocations with the GNU runtime. For example, the method call 50*e4b17023SJohn Marino 51*e4b17023SJohn Marino result = [receiver method]; 52*e4b17023SJohn Marino 53*e4b17023SJohn Marino is compiled by the compiler (with the GNU runtime) into the 54*e4b17023SJohn Marino equivalent of: 55*e4b17023SJohn Marino 56*e4b17023SJohn Marino { 57*e4b17023SJohn Marino IMP function = objc_msg_lookup (receiver, @selector (method)); 58*e4b17023SJohn Marino result = function (receiver, @selector (method)); 59*e4b17023SJohn Marino } 60*e4b17023SJohn Marino 61*e4b17023SJohn Marino so, a call to objc_msg_lookup() determines the IMP (the C function 62*e4b17023SJohn Marino implementing the method) to call. Then, the function is called. 63*e4b17023SJohn Marino If the method takes or returns different arguments, the compiler 64*e4b17023SJohn Marino will cast 'function' to the right type before invoking it, making 65*e4b17023SJohn Marino sure arguments and return value are handled correctly. 66*e4b17023SJohn Marino 67*e4b17023SJohn Marino objc_msg_lookup() must always return a valid function that can be 68*e4b17023SJohn Marino called with the required method signature (otherwise the 69*e4b17023SJohn Marino compiler-generated code shown above could segfault). If 'receiver' 70*e4b17023SJohn Marino is NULL, objc_msg_lookup() returns a C function that does nothing, 71*e4b17023SJohn Marino ignores all its arguments, and returns NULL (see nil_method.c). If 72*e4b17023SJohn Marino 'receiver' does not respond to the selector 'op', objc_msg_lookup() 73*e4b17023SJohn Marino will try to call +resolveClassMethod: or resolveInstanceMethod: as 74*e4b17023SJohn Marino appropriate, and if they return YES, it will try the lookup again 75*e4b17023SJohn Marino (+resolveClassMethod: and +resolveInstanceMethod: can thus install 76*e4b17023SJohn Marino dynamically methods as they are requested). If 77*e4b17023SJohn Marino +resolveClassMethod: or +resolveInstanceMethod: are either not 78*e4b17023SJohn Marino available, or return NO, or return YES but 'receiver' still doesn't 79*e4b17023SJohn Marino implement the 'selector' after calling them, the runtime returns a 80*e4b17023SJohn Marino generic "forwarding" function that can be called with the required 81*e4b17023SJohn Marino method signature and which can process the method invocation 82*e4b17023SJohn Marino according to the forwarding API. There are two runtime hooks that 83*e4b17023SJohn Marino allow Foundation libraries (such as GNUstep-Base) to return their 84*e4b17023SJohn Marino own forwarding function in preference to the runtime ones. When 85*e4b17023SJohn Marino that happens, the Foundation library effectively takes complete 86*e4b17023SJohn Marino control of the forwarding process; any method invocation where the 87*e4b17023SJohn Marino selector is not implemented by the receiver will end up calling a 88*e4b17023SJohn Marino forwarding function chosen by the Foundation library. */ 89*e4b17023SJohn Marino objc_EXPORT IMP objc_msg_lookup (id receiver, SEL op); 90*e4b17023SJohn Marino 91*e4b17023SJohn Marino /* Structure used when a message is send to a class's super class. 92*e4b17023SJohn Marino The compiler generates one of these structures and passes it to 93*e4b17023SJohn Marino objc_msg_lookup_super() when a [super method] call is compiled. */ 94*e4b17023SJohn Marino 95*e4b17023SJohn Marino /* Modern API. */ 96*e4b17023SJohn Marino struct objc_super 97*e4b17023SJohn Marino { 98*e4b17023SJohn Marino id self; /* The receiver of the message. */ 99*e4b17023SJohn Marino Class super_class; /* The superclass of the receiver. */ 100*e4b17023SJohn Marino }; 101*e4b17023SJohn Marino 102*e4b17023SJohn Marino /* This is used by the compiler instead of objc_msg_lookup () when 103*e4b17023SJohn Marino compiling a call to 'super', such as [super method]. This requires 104*e4b17023SJohn Marino sending a message to super->self, but looking up the method as if 105*e4b17023SJohn Marino super->self was in class super->super_class. */ 106*e4b17023SJohn Marino objc_EXPORT IMP objc_msg_lookup_super (struct objc_super *super, SEL sel); 107*e4b17023SJohn Marino 108*e4b17023SJohn Marino /* Hooks for method forwarding. They make it easy to substitute the 109*e4b17023SJohn Marino built-in forwarding with one based on a library, such as ffi, that 110*e4b17023SJohn Marino implement closures, thereby avoiding gcc's __builtin_apply 111*e4b17023SJohn Marino problems. __objc_msg_forward2's result will be preferred over that 112*e4b17023SJohn Marino of __objc_msg_forward if both are set and return non-NULL. */ 113*e4b17023SJohn Marino objc_EXPORT IMP (*__objc_msg_forward)(SEL); 114*e4b17023SJohn Marino objc_EXPORT IMP (*__objc_msg_forward2)(id, SEL); 115*e4b17023SJohn Marino 116*e4b17023SJohn Marino #ifdef __cplusplus 117*e4b17023SJohn Marino } 118*e4b17023SJohn Marino #endif 119*e4b17023SJohn Marino 120*e4b17023SJohn Marino #endif /* not __objc_message_INCLUDE_GNU */ 121