blob: 6df3f7757ef48bd2d2cc6e5b044c13e6c269ec6f [file] [log] [blame]
// 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();
#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> {