Sprout/sprout/functional/equal_to.hpp

/*=============================================================================
  Copyright (c) 2011 RiSK (sscrisk)
  https://github.com/sscrisk/CEL---ConstExpr-Library

  Copyright (c) 2011-2016 Bolero MURAKAMI
  https://github.com/bolero-MURAKAMI/Sprout

  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 SPROUT_FUNCTIONAL_EQUAL_TO_HPP
#define SPROUT_FUNCTIONAL_EQUAL_TO_HPP

#include <utility>
#include <sprout/config.hpp>
#include <sprout/utility/forward.hpp>
#include <sprout/functional/transparent.hpp>

namespace sprout {

	// 20.8.5 Comparisons
	template<typename T = void>
	struct equal_to {
	public:
		typedef T first_argument_type;
		typedef T second_argument_type;
		typedef bool result_type;
	public:
		SPROUT_CONSTEXPR bool operator()(T const& x, T const& y) const {
				return x == y;
		}
	};

	template<>
	struct equal_to<void>
		: public sprout::transparent<>
	{
	public:
		template<typename T, typename U>
		SPROUT_CONSTEXPR decltype(std::declval<T>() == std::declval<U>())
		operator()(T&& x, U&& y)
		const SPROUT_NOEXCEPT_IF_EXPR(std::declval<T>() == std::declval<U>())
		{
			return SPROUT_FORWARD(T, x) == SPROUT_FORWARD(U, y);
		}
	};
}	// namespace sprout

#endif	// #ifndef SPROUT_FUNCTIONAL_EQUAL_TO_HPP