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