120 lines
5.1 KiB
C
120 lines
5.1 KiB
C
/* GNU Objective C Runtime messaging declarations
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Copyright (C) 1993-2020 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef __objc_message_INCLUDE_GNU
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#define __objc_message_INCLUDE_GNU
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#include "objc.h"
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#include "objc-decls.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* This file includes declarations of the messaging functions and
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types. */
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/* Compatibility note: the messaging function is one area where the
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GNU runtime and the Apple/NeXT runtime differ significantly. If
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you can, it is recommended that you use higher-level facilities
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(provided by a Foundation library such as GNUstep Base) to perform
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forwarding or other advanced messaging tricks. */
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/* This function returns the IMP (C function implementing a method) to
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use to invoke the method with selector 'op' of receiver 'receiver'.
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This is the function used by the compiler when compiling method
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invocations with the GNU runtime. For example, the method call
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result = [receiver method];
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is compiled by the compiler (with the GNU runtime) into the
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equivalent of:
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{
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IMP function = objc_msg_lookup (receiver, @selector (method));
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result = function (receiver, @selector (method));
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}
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so, a call to objc_msg_lookup() determines the IMP (the C function
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implementing the method) to call. Then, the function is called.
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If the method takes or returns different arguments, the compiler
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will cast 'function' to the right type before invoking it, making
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sure arguments and return value are handled correctly.
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objc_msg_lookup() must always return a valid function that can be
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called with the required method signature (otherwise the
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compiler-generated code shown above could segfault). If 'receiver'
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is NULL, objc_msg_lookup() returns a C function that does nothing,
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ignores all its arguments, and returns NULL (see nil_method.c). If
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'receiver' does not respond to the selector 'op', objc_msg_lookup()
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will try to call +resolveClassMethod: or resolveInstanceMethod: as
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appropriate, and if they return YES, it will try the lookup again
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(+resolveClassMethod: and +resolveInstanceMethod: can thus install
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dynamically methods as they are requested). If
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+resolveClassMethod: or +resolveInstanceMethod: are either not
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available, or return NO, or return YES but 'receiver' still doesn't
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implement the 'selector' after calling them, the runtime returns a
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generic "forwarding" function that can be called with the required
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method signature and which can process the method invocation
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according to the forwarding API. There are two runtime hooks that
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allow Foundation libraries (such as GNUstep-Base) to return their
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own forwarding function in preference to the runtime ones. When
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that happens, the Foundation library effectively takes complete
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control of the forwarding process; any method invocation where the
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selector is not implemented by the receiver will end up calling a
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forwarding function chosen by the Foundation library. */
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objc_EXPORT IMP objc_msg_lookup (id receiver, SEL op);
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/* Structure used when a message is send to a class's super class.
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The compiler generates one of these structures and passes it to
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objc_msg_lookup_super() when a [super method] call is compiled. */
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/* Modern API. */
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struct objc_super
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{
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id self; /* The receiver of the message. */
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Class super_class; /* The superclass of the receiver. */
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};
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/* This is used by the compiler instead of objc_msg_lookup () when
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compiling a call to 'super', such as [super method]. This requires
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sending a message to super->self, but looking up the method as if
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super->self was in class super->super_class. */
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objc_EXPORT IMP objc_msg_lookup_super (struct objc_super *super, SEL sel);
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/* Hooks for method forwarding. They make it easy to substitute the
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built-in forwarding with one based on a library, such as ffi, that
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implement closures, thereby avoiding gcc's __builtin_apply
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problems. __objc_msg_forward2's result will be preferred over that
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of __objc_msg_forward if both are set and return non-NULL. */
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objc_EXPORT IMP (*__objc_msg_forward)(SEL);
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objc_EXPORT IMP (*__objc_msg_forward2)(id, SEL);
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#ifdef __cplusplus
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}
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#endif
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#endif /* not __objc_message_INCLUDE_GNU */
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