/* GNU Objective C Runtime messaging declarations
- Copyright (C) 1993, 1995, 1996, 2004, 2009,
- 2010 Free Software Foundation, Inc.
+ Copyright (C) 1993-2024 Free Software Foundation, Inc.
This file is part of GCC.
#endif
/* This file includes declarations of the messaging functions and
- types.
-*/
+ types. */
/* Compatibility note: the messaging function is one area where the
GNU runtime and the Apple/NeXT runtime differ significantly. If
you can, it is recommended that you use higher-level facilities
(provided by a Foundation library such as GNUstep Base) to perform
- forwarding or other advanced messaging tricks.
-*/
-
-typedef void* retval_t; /* return value */
-typedef void(*apply_t)(void); /* function pointer */
-typedef union arglist {
- char *arg_ptr;
- char arg_regs[sizeof (char*)];
-} *arglist_t; /* argument frame */
-
-objc_EXPORT IMP objc_msg_lookup(id receiver, SEL op);
-
-/*
- * Structure used when a message is send to a class's super class.
- * The compiler generates one of these structures and passes it to
- * objc_msg_lookup_super.
- */
-typedef struct objc_super {
- id self; /* Id of the object sending the message. */
-#ifdef __cplusplus
- /* The new version of the API will always use 'super_class'. */
- Class super_class;
-#else
- Class class; /* Object's super class. */
-#endif
-} Super, *Super_t;
-
-objc_EXPORT IMP objc_msg_lookup_super(Super_t super, SEL sel);
-
-objc_EXPORT retval_t objc_msg_sendv(id, SEL, arglist_t);
-
-/*
- * Hooks for method forwarding. This makes it easy to substitute a
- * library, such as ffcall, that implements closures, thereby avoiding
- * gcc's __builtin_apply problems. __objc_msg_forward2's result will
- * be preferred over that of __objc_msg_forward if both are set and
- * return non-NULL.
- *
- * TODO: The API should define objc_set_msg_forward_handler () or
- * similar instead of these hooks.
- */
+ forwarding or other advanced messaging tricks. */
+
+/* This function returns the IMP (C function implementing a method) to
+ use to invoke the method with selector 'op' of receiver 'receiver'.
+
+ This is the function used by the compiler when compiling method
+ invocations with the GNU runtime. For example, the method call
+
+ result = [receiver method];
+
+ is compiled by the compiler (with the GNU runtime) into the
+ equivalent of:
+
+ {
+ IMP function = objc_msg_lookup (receiver, @selector (method));
+ result = function (receiver, @selector (method));
+ }
+
+ so, a call to objc_msg_lookup() determines the IMP (the C function
+ implementing the method) to call. Then, the function is called.
+ If the method takes or returns different arguments, the compiler
+ will cast 'function' to the right type before invoking it, making
+ sure arguments and return value are handled correctly.
+
+ objc_msg_lookup() must always return a valid function that can be
+ called with the required method signature (otherwise the
+ compiler-generated code shown above could segfault). If 'receiver'
+ is NULL, objc_msg_lookup() returns a C function that does nothing,
+ ignores all its arguments, and returns NULL (see nil_method.c). If
+ 'receiver' does not respond to the selector 'op', objc_msg_lookup()
+ will try to call +resolveClassMethod: or resolveInstanceMethod: as
+ appropriate, and if they return YES, it will try the lookup again
+ (+resolveClassMethod: and +resolveInstanceMethod: can thus install
+ dynamically methods as they are requested). If
+ +resolveClassMethod: or +resolveInstanceMethod: are either not
+ available, or return NO, or return YES but 'receiver' still doesn't
+ implement the 'selector' after calling them, the runtime returns a
+ generic "forwarding" function that can be called with the required
+ method signature and which can process the method invocation
+ according to the forwarding API. There are two runtime hooks that
+ allow Foundation libraries (such as GNUstep-Base) to return their
+ own forwarding function in preference to the runtime ones. When
+ that happens, the Foundation library effectively takes complete
+ control of the forwarding process; any method invocation where the
+ selector is not implemented by the receiver will end up calling a
+ forwarding function chosen by the Foundation library. */
+objc_EXPORT IMP objc_msg_lookup (id receiver, SEL op);
+
+/* Structure used when a message is send to a class's super class.
+ The compiler generates one of these structures and passes it to
+ objc_msg_lookup_super() when a [super method] call is compiled. */
+
+/* Modern API. */
+struct objc_super
+{
+ id self; /* The receiver of the message. */
+ Class super_class; /* The superclass of the receiver. */
+};
+
+/* This is used by the compiler instead of objc_msg_lookup () when
+ compiling a call to 'super', such as [super method]. This requires
+ sending a message to super->self, but looking up the method as if
+ super->self was in class super->super_class. */
+objc_EXPORT IMP objc_msg_lookup_super (struct objc_super *super, SEL sel);
+
+/* Hooks for method forwarding. They make it easy to substitute the
+ built-in forwarding with one based on a library, such as ffi, that
+ implement closures, thereby avoiding gcc's __builtin_apply
+ problems. __objc_msg_forward2's result will be preferred over that
+ of __objc_msg_forward if both are set and return non-NULL. */
objc_EXPORT IMP (*__objc_msg_forward)(SEL);
objc_EXPORT IMP (*__objc_msg_forward2)(id, SEL);
projects / thirdparty / gcc.git / blobdiff