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+/*!
+@file
+Defines `boost::hana::comparing`.
+
+@copyright Louis Dionne 2013-2016
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_COMPARING_HPP
+#define BOOST_HANA_COMPARING_HPP
+
+#include <boost/hana/fwd/comparing.hpp>
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/equal.hpp>
+
+#include <type_traits>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ namespace detail {
+ template <typename F>
+ struct equal_by {
+ F f;
+
+ template <typename X, typename Y>
+ constexpr auto operator()(X&& x, Y&& y) const&
+ { return hana::equal(f(static_cast<X&&>(x)), f(static_cast<Y&&>(y))); }
+
+ template <typename X, typename Y>
+ constexpr auto operator()(X&& x, Y&& y) &
+ { return hana::equal(f(static_cast<X&&>(x)), f(static_cast<Y&&>(y))); }
+ };
+ }
+
+ //! @cond
+ template <typename F>
+ constexpr auto comparing_t::operator()(F&& f) const {
+ return detail::equal_by<typename std::decay<F>::type>{static_cast<F&&>(f)};
+ }
+ //! @endcond
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_COMPARING_HPP