Manual.hxx

/*
 * Copyright (C) 2013 Max Kellermann <max@duempel.org>
 *
 * 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.
 */

#ifndef MPD_MANUAL_HXX
#define MPD_MANUAL_HXX

#include "Compiler.h"

#include <new>
#include <utility>

#if !defined(__clang__) && __GNUC__ && !GCC_CHECK_VERSION(4,8)
#include <type_traits>
#endif

#include <assert.h>

#if defined(__clang__) || GCC_CHECK_VERSION(4,7)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wstrict-aliasing"
#endif

/**
 * 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 {
#if !defined(__clang__) && __GNUC__ && !GCC_CHECK_VERSION(4,8)
	/* no alignas() on gcc < 4.8: apply worst-case fallback */
	__attribute__((aligned(8)))
#else
	alignas(T)
#endif
	char data[sizeof(T)];

#ifndef NDEBUG
	bool initialized;
#endif

public:
#ifndef NDEBUG
	Manual():initialized(false) {}
	~Manual() {
		assert(!initialized);
	}
#endif

	template<typename... Args>
	void Construct(Args&&... args) {
		assert(!initialized);

		void *p = data;
		new(p) T(std::forward<Args>(args)...);

#ifndef NDEBUG
		initialized = true;
#endif
	}

	void Destruct() {
		assert(initialized);

		T *t = (T *)data;
		t->T::~T();

#ifndef NDEBUG
		initialized = false;
#endif
	}

	operator T &() {
		return *(T *)data;
	}

	operator const T &() const {
		return *(const T *)data;
	}

	T *operator->() {
		return (T *)data;
	}

	const T *operator->() const {
		return (T *)data;
	}
};

#if defined(__clang__) || GCC_VERSION >= 40700
#pragma GCC diagnostic pop
#endif

#endif