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// Copyright (c) 2012 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.
// ManualConstructor statically-allocates space in which to store some
// object, but does not initialize it. You can then call the constructor
// and destructor for the object yourself as you see fit. This is useful
// for memory management optimizations, where you want to initialize and
// destroy an object multiple times but only allocate it once.
//
// (When I say ManualConstructor statically allocates space, I mean that
// the ManualConstructor object itself is forced to be the right size.)
//
// For example usage, check out base/containers/small_map.h.
#ifndef BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
#define BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
#include <stddef.h>
#include "base/compiler_specific.h"
#include "base/memory/aligned_memory.h"
namespace base {
template <typename Type>
class ManualConstructor {
public:
// No constructor or destructor because one of the most useful uses of
// this class is as part of a union, and members of a union cannot have
// constructors or destructors. And, anyway, the whole point of this
// class is to bypass these.
// Support users creating arrays of ManualConstructor<>s. This ensures that
// the array itself has the correct alignment.
static void* operator new[](size_t size) {
return AlignedAlloc(size, ALIGNOF(Type));
}
static void operator delete[](void* mem) {
AlignedFree(mem);
}
inline Type* get() {
return space_.template data_as<Type>();
}
inline const Type* get() const {
return space_.template data_as<Type>();
}
inline Type* operator->() { return get(); }
inline const Type* operator->() const { return get(); }
inline Type& operator*() { return *get(); }
inline const Type& operator*() const { return *get(); }
template <typename... Ts>
inline void Init(Ts&&... params) {
new(space_.void_data()) Type(std::forward<Ts>(params)...);
}
inline void InitFromMove(ManualConstructor<Type>&& o) {
Init(std::move(*o));
}
inline void Destroy() {
get()->~Type();
}
private:
AlignedMemory<sizeof(Type), ALIGNOF(Type)> space_;
};
} // namespace base
#endif // BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
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