boost/scope/detail/compact_storage.hpp
/*
* Distributed under the Boost Software License, Version 1.0.
* (See accompanying file LICENSE_1_0.txt or copy at
* https://www.boost.org/LICENSE_1_0.txt)
*
* Copyright (c) 2022 Andrey Semashev
*/
/*!
* \file scope/detail/compact_storage.hpp
*
* This header contains utility helpers for implementing compact storage
* for class members. In particular, it allows to leverage empty base optimization (EBO).
*/
#ifndef BOOST_SCOPE_DETAIL_COMPACT_STORAGE_HPP_INCLUDED_
#define BOOST_SCOPE_DETAIL_COMPACT_STORAGE_HPP_INCLUDED_
#include <type_traits>
#include <boost/scope/detail/config.hpp>
#include <boost/scope/detail/type_traits/is_final.hpp>
#include <boost/scope/detail/type_traits/negation.hpp>
#include <boost/scope/detail/type_traits/conjunction.hpp>
#include <boost/scope/detail/header.hpp>
#ifdef BOOST_HAS_PRAGMA_ONCE
#pragma once
#endif
namespace boost {
namespace scope {
namespace detail {
//! The class allows to place data members in the tail padding of type \a T if the user's class derives from it
template<
typename T,
typename Tag = void,
bool = detail::conjunction< std::is_class< T >, detail::negation< detail::is_final< T > > >::value
>
class compact_storage :
private T
{
public:
template< typename... Args >
constexpr compact_storage(Args&&... args) noexcept(std::is_nothrow_constructible< T, Args... >::value) :
T(static_cast< Args&& >(args)...)
{
}
compact_storage(compact_storage&&) = default;
compact_storage& operator= (compact_storage&&) = default;
compact_storage(compact_storage const&) = default;
compact_storage& operator= (compact_storage const&) = default;
T& get() noexcept
{
return *static_cast< T* >(this);
}
T const& get() const noexcept
{
return *static_cast< const T* >(this);
}
};
template< typename T, typename Tag >
class compact_storage< T, Tag, false >
{
private:
T m_data;
public:
template< typename... Args >
constexpr compact_storage(Args&&... args) noexcept(std::is_nothrow_constructible< T, Args... >::value) :
m_data(static_cast< Args&& >(args)...)
{
}
compact_storage(compact_storage&&) = default;
compact_storage& operator= (compact_storage&&) = default;
compact_storage(compact_storage const&) = default;
compact_storage& operator= (compact_storage const&) = default;
T& get() noexcept
{
return m_data;
}
T const& get() const noexcept
{
return m_data;
}
};
} // namespace detail
} // namespace scope
} // namespace boost
#include <boost/scope/detail/footer.hpp>
#endif // BOOST_SCOPE_DETAIL_COMPACT_STORAGE_HPP_INCLUDED_