michael@0: // Copyright (c) 2008 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: // Support for using the Singleton<T> pattern with Objective-C objects.  A
michael@0: // SingletonObjC is the same as a Singleton, except the default traits are
michael@0: // appropriate for Objective-C objects.  A typical Objective-C object of type
michael@0: // NSExampleType can be maintained as a singleton and accessed with:
michael@0: //
michael@0: //   NSExampleType* exampleSingleton = SingletonObjC<NSExampleType>::get();
michael@0: //
michael@0: // The first time this is used, it will create exampleSingleton as the result
michael@0: // of [[NSExampleType alloc] init].  Subsequent calls will return the same
michael@0: // NSExampleType* object.  The object will be released by calling
michael@0: // -[NSExampleType release] when Singleton's atexit routines run
michael@0: // (see singleton.h).
michael@0: //
michael@0: // For Objective-C objects initialized through means other than the
michael@0: // no-parameter -init selector, DefaultSingletonObjCTraits may be extended
michael@0: // as needed:
michael@0: //
michael@0: //   struct FooSingletonTraits : public DefaultSingletonObjCTraits<Foo> {
michael@0: //     static Foo* New() {
michael@0: //       return [[Foo alloc] initWithName:@"selecty"];
michael@0: //     }
michael@0: //   }
michael@0: //   ...
michael@0: //   Foo* widgetSingleton = SingletonObjC<Foo, FooSingletonTraits>::get();
michael@0: 
michael@0: #ifndef BASE_SINGLETON_OBJC_H_
michael@0: #define BASE_SINGLETON_OBJC_H_
michael@0: 
michael@0: #import <Foundation/Foundation.h>
michael@0: #include "base/singleton.h"
michael@0: 
michael@0: // Singleton traits usable to manage traditional Objective-C objects, which
michael@0: // are instantiated by sending |alloc| and |init| messages, and are deallocated
michael@0: // in a memory-managed environment when their retain counts drop to 0 by
michael@0: // sending |release| messages.
michael@0: template<typename Type>
michael@0: struct DefaultSingletonObjCTraits : public DefaultSingletonTraits<Type> {
michael@0:   static Type* New() {
michael@0:     return [[Type alloc] init];
michael@0:   }
michael@0: 
michael@0:   static void Delete(Type* object) {
michael@0:     [object release];
michael@0:   }
michael@0: };
michael@0: 
michael@0: // Exactly like Singleton, but without the DefaultSingletonObjCTraits as the
michael@0: // default trait class.  This makes it straightforward for Objective-C++ code
michael@0: // to hold Objective-C objects as singletons.
michael@0: template<typename Type,
michael@0:          typename Traits = DefaultSingletonObjCTraits<Type>,
michael@0:          typename DifferentiatingType = Type>
michael@0: class SingletonObjC : public Singleton<Type, Traits, DifferentiatingType> {
michael@0: };
michael@0: 
michael@0: #endif  // BASE_SINGLETON_OBJC_H_