1// Copyright (c) 2011 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// Support for using the Singleton<T> pattern with Objective-C objects.  A
6// SingletonObjC is the same as a Singleton, except the default traits are
7// appropriate for Objective-C objects.  A typical Objective-C object of type
8// NSExampleType can be maintained as a singleton and accessed with:
9//
10//   NSExampleType* exampleSingleton = SingletonObjC<NSExampleType>::get();
11//
12// The first time this is used, it will create exampleSingleton as the result
13// of [[NSExampleType alloc] init].  Subsequent calls will return the same
14// NSExampleType* object.  The object will be released by calling
15// -[NSExampleType release] when Singleton's atexit routines run
16// (see singleton.h).
17//
18// For Objective-C objects initialized through means other than the
19// no-parameter -init selector, DefaultSingletonObjCTraits may be extended
20// as needed:
21//
22//   struct FooSingletonTraits : public DefaultSingletonObjCTraits<Foo> {
23//     static Foo* New() {
24//       return [[Foo alloc] initWithName:@"selecty"];
25//     }
26//   };
27//   ...
28//   Foo* widgetSingleton = SingletonObjC<Foo, FooSingletonTraits>::get();
29
30#ifndef BASE_MEMORY_SINGLETON_OBJC_H_
31#define BASE_MEMORY_SINGLETON_OBJC_H_
32#pragma once
33
34#import <Foundation/Foundation.h>
35#include "base/memory/singleton.h"
36
37// Singleton traits usable to manage traditional Objective-C objects, which
38// are instantiated by sending |alloc| and |init| messages, and are deallocated
39// in a memory-managed environment when their retain counts drop to 0 by
40// sending |release| messages.
41template<typename Type>
42struct DefaultSingletonObjCTraits : public DefaultSingletonTraits<Type> {
43  static Type* New() {
44    return [[Type alloc] init];
45  }
46
47  static void Delete(Type* object) {
48    [object release];
49  }
50};
51
52// Exactly like Singleton, but without the DefaultSingletonObjCTraits as the
53// default trait class.  This makes it straightforward for Objective-C++ code
54// to hold Objective-C objects as singletons.
55template<typename Type,
56         typename Traits = DefaultSingletonObjCTraits<Type>,
57         typename DifferentiatingType = Type>
58class SingletonObjC : public Singleton<Type, Traits, DifferentiatingType> {
59};
60
61#endif  // BASE_MEMORY_SINGLETON_OBJC_H_
62