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+// Copyright (c) 2011 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_MEMORY_SINGLETON_OBJC_H_
+#define BASE_MEMORY_SINGLETON_OBJC_H_
+#pragma once
+
+#import <Foundation/Foundation.h>
+#include "base/memory/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_MEMORY_SINGLETON_OBJC_H_