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// EXTConcreteProtocol.h
// extobjc
// Created by Justin Spahr-Summers on 2010-11-09.
// Copyright (C) 2012 Justin Spahr-Summers.
// Released under the MIT license.
#import <objc/runtime.h>
#import <stdio.h>
#import "metamacros.h"
* Used to list methods with concrete implementations within a \@protocol
* definition.
* Semantically, this is equivalent to using \@optional, but is recommended for
* documentation reasons. Although concrete protocol methods are optional in the
* sense that conforming objects don't need to implement them, they are,
* however, always guaranteed to be present.
#define concrete \
* Defines a "concrete protocol," which can provide default implementations of
* methods within protocol \a NAME. A \@protocol block should exist in a header
* file, and a corresponding \@concreteprotocol block in an implementation file.
* Any object that declares itself to conform to protocol \a NAME will receive
* its method implementations \e only if no method by the same name already
* exists.
* @code
// MyProtocol.h
@protocol MyProtocol
- (void)someRequiredMethod;
- (void)someOptionalMethod;
- (BOOL)isConcrete;
// MyProtocol.m
- (BOOL)isConcrete {
return YES;
// this will not actually get added to conforming classes, since they are
// required to have their own implementation
- (void)someRequiredMethod {}
* @endcode
* If a concrete protocol \c X conforms to another concrete protocol \c Y, any
* concrete implementations in \c X will be prioritized over those in \c Y. In
* other words, if both protocols provide a default implementation for a method,
* the one from \c X (the most descendant) is the one that will be loaded into
* any class that conforms to \c X. Classes that conform to \c Y will naturally
* only use the implementations from \c Y.
* To perform tasks when a concrete protocol is loaded, use the \c +initialize
* method. This method in a concrete protocol is treated similarly to \c +load
* in categories – it will be executed at most once per concrete protocol, and
* is not added to any classes which receive the concrete protocol's methods.
* The protocol's methods will have been added to all conforming classes at the
* time that \c +initialize is invoked. If no class conforms to the concrete
* protocol, \c +initialize may never be called.
* @note You cannot define instance variables in a concrete protocol.
* @warning You should not invoke methods against \c super in the implementation
* of a concrete protocol, as the superclass may not be the type you expect (and
* may not even inherit from \c NSObject).
#define concreteprotocol(NAME) \
* create a class used to contain all the methods used in this protocol
*/ \
interface NAME ## _ProtocolMethodContainer : NSObject < NAME > {} \
@end \
@implementation NAME ## _ProtocolMethodContainer \
* when this class is loaded into the runtime, add the concrete protocol
* into the list we have of them
*/ \
+ (void)load { \
* passes the actual protocol as the first parameter, then this class as
* the second
*/ \
if (!ext_addConcreteProtocol(objc_getProtocol(metamacro_stringify(NAME)), self)) \
fprintf(stderr, "ERROR: Could not load concrete protocol %s\n", metamacro_stringify(NAME)); \
} \
* using the "constructor" function attribute, we can ensure that this
* function is executed only AFTER all the Objective-C runtime setup (i.e.,
* after all +load methods have been executed)
*/ \
__attribute__((constructor)) \
static void ext_ ## NAME ## _inject (void) { \
* use this injection point to mark this concrete protocol as ready for
* loading
*/ \
ext_loadConcreteProtocol(objc_getProtocol(metamacro_stringify(NAME))); \
/*** implementation details follow ***/
BOOL ext_addConcreteProtocol (Protocol *protocol, Class methodContainer);
void ext_loadConcreteProtocol (Protocol *protocol);