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73 lines
1.8 KiB
C++
73 lines
1.8 KiB
C++
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/*=============================================================================
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Copyright (c) 2012 Paul Fultz II
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identity.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_FUNCTION_IDENTITY_H
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#define BOOST_HOF_GUARD_FUNCTION_IDENTITY_H
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/// identity
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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 `identity` function is an unary function object that returns whats given to it.
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///
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/// Semantics
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/// ---------
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///
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/// assert(identity(x) == x);
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///
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/// Synopsis
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/// --------
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///
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/// template<class T>
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/// constexpr T identity(T&& x);
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///
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#include <utility>
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#include <initializer_list>
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#include <boost/hof/detail/forward.hpp>
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#include <boost/hof/detail/static_const_var.hpp>
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namespace boost { namespace hof { namespace identity_detail {
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struct identity_base
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{
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template<class T>
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constexpr T operator()(T&& x) const
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noexcept(std::is_reference<T>::value || BOOST_HOF_IS_NOTHROW_MOVE_CONSTRUCTIBLE(T))
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{
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return BOOST_HOF_FORWARD(T)(x);
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}
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template<class T>
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constexpr std::initializer_list<T>& operator()(std::initializer_list<T>& x) const 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 std::initializer_list<T>& operator()(const std::initializer_list<T>& x) const 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 std::initializer_list<T> operator()(std::initializer_list<T>&& x) const noexcept(noexcept(std::initializer_list<T>(std::move(x))))
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{
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return BOOST_HOF_FORWARD(std::initializer_list<T>)(x);
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}
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};
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}
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BOOST_HOF_DECLARE_STATIC_VAR(identity, identity_detail::identity_base);
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}} // namespace boost::hof
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#endif
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