1// Copyright (c) 2012 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// ManualConstructor statically-allocates space in which to store some
6// object, but does not initialize it.  You can then call the constructor
7// and destructor for the object yourself as you see fit.  This is useful
8// for memory management optimizations, where you want to initialize and
9// destroy an object multiple times but only allocate it once.
10//
11// (When I say ManualConstructor statically allocates space, I mean that
12// the ManualConstructor object itself is forced to be the right size.)
13//
14// For example usage, check out base/containers/small_map.h.
15
16#ifndef BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
17#define BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
18
19#include <stddef.h>
20
21#include "base/memory/aligned_memory.h"
22
23namespace base {
24
25template <typename Type>
26class ManualConstructor {
27 public:
28  // No constructor or destructor because one of the most useful uses of
29  // this class is as part of a union, and members of a union cannot have
30  // constructors or destructors.  And, anyway, the whole point of this
31  // class is to bypass these.
32
33  // Support users creating arrays of ManualConstructor<>s.  This ensures that
34  // the array itself has the correct alignment.
35  static void* operator new[](size_t size) {
36#if defined(COMPILER_MSVC)
37    return AlignedAlloc(size, __alignof(Type));
38#else
39    return AlignedAlloc(size, __alignof__(Type));
40#endif
41  }
42  static void operator delete[](void* mem) {
43    AlignedFree(mem);
44  }
45
46  inline Type* get() {
47    return space_.template data_as<Type>();
48  }
49  inline const Type* get() const  {
50    return space_.template data_as<Type>();
51  }
52
53  inline Type* operator->() { return get(); }
54  inline const Type* operator->() const { return get(); }
55
56  inline Type& operator*() { return *get(); }
57  inline const Type& operator*() const { return *get(); }
58
59  // You can pass up to eight constructor arguments as arguments of Init().
60  inline void Init() {
61    new(space_.void_data()) Type;
62  }
63
64  template <typename T1>
65  inline void Init(const T1& p1) {
66    new(space_.void_data()) Type(p1);
67  }
68
69  template <typename T1, typename T2>
70  inline void Init(const T1& p1, const T2& p2) {
71    new(space_.void_data()) Type(p1, p2);
72  }
73
74  template <typename T1, typename T2, typename T3>
75  inline void Init(const T1& p1, const T2& p2, const T3& p3) {
76    new(space_.void_data()) Type(p1, p2, p3);
77  }
78
79  template <typename T1, typename T2, typename T3, typename T4>
80  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4) {
81    new(space_.void_data()) Type(p1, p2, p3, p4);
82  }
83
84  template <typename T1, typename T2, typename T3, typename T4, typename T5>
85  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
86                   const T5& p5) {
87    new(space_.void_data()) Type(p1, p2, p3, p4, p5);
88  }
89
90  template <typename T1, typename T2, typename T3, typename T4, typename T5,
91            typename T6>
92  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
93                   const T5& p5, const T6& p6) {
94    new(space_.void_data()) Type(p1, p2, p3, p4, p5, p6);
95  }
96
97  template <typename T1, typename T2, typename T3, typename T4, typename T5,
98            typename T6, typename T7>
99  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
100                   const T5& p5, const T6& p6, const T7& p7) {
101    new(space_.void_data()) Type(p1, p2, p3, p4, p5, p6, p7);
102  }
103
104  template <typename T1, typename T2, typename T3, typename T4, typename T5,
105            typename T6, typename T7, typename T8>
106  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
107                   const T5& p5, const T6& p6, const T7& p7, const T8& p8) {
108    new(space_.void_data()) Type(p1, p2, p3, p4, p5, p6, p7, p8);
109  }
110
111  inline void Destroy() {
112    get()->~Type();
113  }
114
115 private:
116#if defined(COMPILER_MSVC)
117  AlignedMemory<sizeof(Type), __alignof(Type)> space_;
118#else
119  AlignedMemory<sizeof(Type), __alignof__(Type)> space_;
120#endif
121};
122
123}  // namespace base
124
125#endif  // BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
126