mpd/src/util/Manual.hxx

127 lines
3.0 KiB
C++
Raw Normal View History

2013-01-30 23:48:34 +01:00
/*
2022-05-31 16:10:28 +02:00
* Copyright 2013-2022 Max Kellermann <max.kellermann@gmail.com>
2013-01-30 23:48:34 +01:00
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*/
2022-05-31 16:10:28 +02:00
#pragma once
2013-01-30 23:48:34 +01:00
#include <cassert>
2013-01-30 23:48:34 +01:00
#include <new>
#include <utility>
2013-01-30 23:48:34 +01:00
2017-07-05 12:25:20 +02:00
#if defined(__GNUC__) || defined(__clang__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wstrict-aliasing"
#endif
2013-01-30 23:48:34 +01:00
/**
* Container for an object that gets constructed and destructed
* manually. The object is constructed in-place, and therefore
* without allocation overhead. It can be constructed and destructed
* repeatedly.
*/
template<class T>
class Manual {
alignas(T)
2013-01-30 23:48:34 +01:00
char data[sizeof(T)];
#ifndef NDEBUG
2017-07-05 12:12:41 +02:00
bool initialized = false;
2013-01-30 23:48:34 +01:00
#endif
public:
#ifndef NDEBUG
2022-05-31 16:10:28 +02:00
~Manual() noexcept {
2013-01-30 23:48:34 +01:00
assert(!initialized);
}
#endif
2018-08-20 15:35:43 +02:00
/**
* Cast a value reference to the containing Manual instance.
*/
2022-05-31 16:10:28 +02:00
static constexpr Manual<T> &Cast(T &value) noexcept {
2018-08-20 15:35:43 +02:00
return reinterpret_cast<Manual<T> &>(value);
}
2013-01-30 23:48:34 +01:00
template<typename... Args>
void Construct(Args&&... args) {
assert(!initialized);
void *p = data;
new(p) T(std::forward<Args>(args)...);
#ifndef NDEBUG
initialized = true;
#endif
}
2022-05-31 16:10:28 +02:00
void Destruct() noexcept {
2013-01-30 23:48:34 +01:00
assert(initialized);
2014-12-09 23:08:53 +01:00
T &t = Get();
t.T::~T();
2013-01-30 23:48:34 +01:00
#ifndef NDEBUG
initialized = false;
#endif
}
2022-05-31 16:10:28 +02:00
T &Get() noexcept {
2014-12-09 23:08:22 +01:00
assert(initialized);
void *p = static_cast<void *>(data);
return *static_cast<T *>(p);
2013-01-30 23:48:34 +01:00
}
2022-05-31 16:10:28 +02:00
const T &Get() const noexcept {
2014-12-09 23:08:22 +01:00
assert(initialized);
const void *p = static_cast<const void *>(data);
return *static_cast<const T *>(p);
2013-01-30 23:48:34 +01:00
}
2022-05-31 16:10:28 +02:00
operator T &() noexcept {
return Get();
}
2022-05-31 16:10:28 +02:00
operator const T &() const noexcept {
return Get();
}
2022-05-31 16:10:28 +02:00
T *operator->() noexcept {
return &Get();
2013-01-30 23:48:34 +01:00
}
2022-05-31 16:10:28 +02:00
const T *operator->() const noexcept {
return &Get();
2013-01-30 23:48:34 +01:00
}
};
2017-07-05 12:25:20 +02:00
#if defined(__GNUC__) || defined(__clang__)
#pragma GCC diagnostic pop
#endif