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 // Copyright (c) 2008 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 // Support for using the Singleton<T> pattern with Objective-C objects.  A

 // SingletonObjC is the same as a Singleton, except the default traits are

 // appropriate for Objective-C objects.  A typical Objective-C object of type

 // NSExampleType can be maintained as a singleton and accessed with:

 //

 //   NSExampleType* exampleSingleton = SingletonObjC<NSExampleType>::get();

 //

 // The first time this is used, it will create exampleSingleton as the result

 // of [[NSExampleType alloc] init].  Subsequent calls will return the same

 // NSExampleType* object.  The object will be released by calling

 // -[NSExampleType release] when Singleton's atexit routines run

 // (see singleton.h).

 //

 // For Objective-C objects initialized through means other than the

 // no-parameter -init selector, DefaultSingletonObjCTraits may be extended

 // as needed:

 //

 //   struct FooSingletonTraits : public DefaultSingletonObjCTraits<Foo> {

 //     static Foo* New() {

 //       return [[Foo alloc] initWithName:@"selecty"];

 //     }

 //   }

 //   ...

 //   Foo* widgetSingleton = SingletonObjC<Foo, FooSingletonTraits>::get();

 #ifndef BASE_SINGLETON_OBJC_H_

 #define BASE_SINGLETON_OBJC_H_

 #import <Foundation/Foundation.h>

 #include "base/singleton.h"

 // Singleton traits usable to manage traditional Objective-C objects, which

 // are instantiated by sending |alloc| and |init| messages, and are deallocated

 // in a memory-managed environment when their retain counts drop to 0 by

 // sending |release| messages.

 template<typename Type>

 struct DefaultSingletonObjCTraits : public DefaultSingletonTraits<Type> {

   static Type* New() {

     return [[Type alloc] init];

   }

   static void Delete(Type* object) {

     [object release];

   }

 };

 // Exactly like Singleton, but without the DefaultSingletonObjCTraits as the

 // default trait class.  This makes it straightforward for Objective-C++ code

 // to hold Objective-C objects as singletons.

 template<typename Type,

          typename Traits = DefaultSingletonObjCTraits<Type>,

          typename DifferentiatingType = Type>

 class SingletonObjC : public Singleton<Type, Traits, DifferentiatingType> {

 };

 #endif  // BASE_SINGLETON_OBJC_H_