63e88f80
 Hu Chunming
提交三方库
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/*=============================================================================
Copyright (c) 2012 Paul Fultz II
identity.h
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
==============================================================================*/
#ifndef BOOST_HOF_GUARD_FUNCTION_IDENTITY_H
#define BOOST_HOF_GUARD_FUNCTION_IDENTITY_H
/// identity
/// ========
///
/// Description
/// -----------
///
/// The `identity` function is an unary function object that returns whats given to it.
///
/// Semantics
/// ---------
///
/// assert(identity(x) == x);
///
/// Synopsis
/// --------
///
/// template<class T>
/// constexpr T identity(T&& x);
///
#include <utility>
#include <initializer_list>
#include <boost/hof/detail/forward.hpp>
#include <boost/hof/detail/static_const_var.hpp>
namespace boost { namespace hof { namespace identity_detail {
struct identity_base
{
template<class T>
constexpr T operator()(T&& x) const
noexcept(std::is_reference<T>::value || BOOST_HOF_IS_NOTHROW_MOVE_CONSTRUCTIBLE(T))
{
return BOOST_HOF_FORWARD(T)(x);
}
template<class T>
constexpr std::initializer_list<T>& operator()(std::initializer_list<T>& x) const noexcept
{
return x;
}
template<class T>
constexpr const std::initializer_list<T>& operator()(const std::initializer_list<T>& x) const noexcept
{
return x;
}
template<class T>
constexpr std::initializer_list<T> operator()(std::initializer_list<T>&& x) const noexcept(noexcept(std::initializer_list<T>(std::move(x))))
{
return BOOST_HOF_FORWARD(std::initializer_list<T>)(x);
}
};
}
BOOST_HOF_DECLARE_STATIC_VAR(identity, identity_detail::identity_base);
}} // namespace boost::hof
#endif
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