/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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alias.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef BOOST_HOF_GUARD_ALIAS_H
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#define BOOST_HOF_GUARD_ALIAS_H
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#include <boost/hof/returns.hpp>
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#include <boost/hof/detail/delegate.hpp>
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#include <boost/hof/detail/move.hpp>
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#include <boost/hof/detail/holder.hpp>
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#include <boost/hof/config.hpp>
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/// alias
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/// =====
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///
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/// Description
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/// -----------
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///
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/// The `alias` class wraps a type with a new type that can be tagged by the
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/// user. This allows defining extra attributes about the type outside of the
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/// type itself. There are three different ways the value can be stored: as a
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/// member variable, by inheritance, or as a static member variable. The value
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/// can be retrieved uniformily using the `alias_value` function.
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///
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/// Synopsis
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/// --------
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///
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/// // Alias the type using a member variable
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/// template<class T, class Tag=void>
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/// class alias;
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///
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/// // Alias the type by inheriting
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/// template<class T, class Tag=void>
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/// class alias_inherit;
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///
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/// // Alias the type using a static variable
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/// template<class T, class Tag=void>
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/// class alias_static;
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///
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/// // Retrieve tag from alias
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/// template<class Alias>
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/// class alias_tag;
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///
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/// // Check if type has a certian tag
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/// template<class T, class Tag>
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/// class has_tag;
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///
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/// // Retrieve value from alias
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/// template<class Alias>
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/// constexpr auto alias_value(Alias&&);
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///
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#ifdef _MSC_VER
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#pragma warning(push)
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#pragma warning(disable: 4579)
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#endif
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namespace boost { namespace hof {
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template<class T>
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struct alias_tag;
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template<class T, class Tag, class=void>
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struct has_tag
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: std::false_type
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{};
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template<class T, class Tag>
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struct has_tag<T, Tag, typename detail::holder<
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typename alias_tag<T>::type
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>::type>
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: std::is_same<typename alias_tag<T>::type, Tag>
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{};
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namespace detail {
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template<class T>
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constexpr T& lvalue(T& x) noexcept
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{
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return x;
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}
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template<class T>
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constexpr const T& lvalue(const T& x) noexcept
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{
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return x;
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}
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}
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#define BOOST_HOF_UNARY_PERFECT_FOREACH(m) \
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m(const&, boost::hof::detail::lvalue) \
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m(&, boost::hof::detail::lvalue) \
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m(&&, boost::hof::move) \
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template<class T, class Tag=void>
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struct alias
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{
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T value;
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BOOST_HOF_DELEGATE_CONSTRUCTOR(alias, T, value)
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};
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#define BOOST_HOF_DETAIL_ALIAS_GET_VALUE(ref, move) \
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template<class Tag, class T, class... Ts> \
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constexpr auto alias_value(alias<T, Tag> ref a, Ts&&...) BOOST_HOF_RETURNS(move(a.value))
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BOOST_HOF_UNARY_PERFECT_FOREACH(BOOST_HOF_DETAIL_ALIAS_GET_VALUE)
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template<class T, class Tag>
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struct alias_tag<alias<T, Tag>>
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{ typedef Tag type; };
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template<class T, class Tag=void>
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struct alias_inherit
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#if (defined(__GNUC__) && !defined (__clang__))
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: std::conditional<(std::is_class<T>::value), T, alias<T>>::type
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#else
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: T
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#endif
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{
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BOOST_HOF_INHERIT_CONSTRUCTOR(alias_inherit, T)
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};
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#define BOOST_HOF_DETAIL_ALIAS_INHERIT_GET_VALUE(ref, move) \
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template<class Tag, class T, class... Ts, class=typename std::enable_if<(BOOST_HOF_IS_CLASS(T))>::type> \
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constexpr T ref alias_value(alias_inherit<T, Tag> ref a, Ts&&...) BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(move(a)) \
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{ \
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return move(a); \
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}
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BOOST_HOF_UNARY_PERFECT_FOREACH(BOOST_HOF_DETAIL_ALIAS_INHERIT_GET_VALUE)
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template<class T, class Tag>
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struct alias_tag<alias_inherit<T, Tag>>
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{ typedef Tag type; };
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namespace detail {
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template<class T, class Tag>
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struct alias_static_storage
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{
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#ifdef _MSC_VER
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// Since we disable the error for 4579 on MSVC, which leaves the static
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// member unitialized at runtime, it is, therefore, only safe to use this
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// class on types that are empty with constructors that have no possible
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// side effects.
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static_assert(BOOST_HOF_IS_EMPTY(T) &&
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BOOST_HOF_IS_LITERAL(T) &&
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BOOST_HOF_IS_DEFAULT_CONSTRUCTIBLE(T), "In-class initialization is not yet implemented on MSVC");
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#endif
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static constexpr T value = T();
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};
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template<class T, class Tag>
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constexpr T alias_static_storage<T, Tag>::value;
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}
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template<class T, class Tag=void>
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struct alias_static
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{
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template<class... Ts, BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(T, Ts...)>
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constexpr alias_static(Ts&&...) noexcept
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{}
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};
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template<class Tag, class T, class... Ts>
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constexpr const T& alias_value(const alias_static<T, Tag>&, Ts&&...) noexcept
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{
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return detail::alias_static_storage<T, Tag>::value;
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}
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template<class T, class Tag>
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struct alias_tag<alias_static<T, Tag>>
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{ typedef Tag type; };
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namespace detail {
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template<class T, class Tag>
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struct alias_try_inherit
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: std::conditional<(BOOST_HOF_IS_CLASS(T) && !BOOST_HOF_IS_FINAL(T) && !BOOST_HOF_IS_POLYMORPHIC(T)),
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alias_inherit<T, Tag>,
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alias<T, Tag>
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>
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{};
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#if BOOST_HOF_HAS_EBO
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template<class T, class Tag>
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struct alias_empty
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: std::conditional<(BOOST_HOF_IS_EMPTY(T)),
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typename alias_try_inherit<T, Tag>::type,
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alias<T, Tag>
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>
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{};
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#else
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template<class T, class Tag>
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struct alias_empty
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: std::conditional<
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BOOST_HOF_IS_EMPTY(T) &&
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BOOST_HOF_IS_LITERAL(T) &&
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BOOST_HOF_IS_DEFAULT_CONSTRUCTIBLE(T),
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alias_static<T, Tag>,
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alias<T, Tag>
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>
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{};
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#endif
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}
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}} // namespace boost::hof
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#ifdef _MSC_VER
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#pragma warning(pop)
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#endif
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#endif
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