63e88f80
 Hu Chunming
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/*!
@file
Defines `boost::hana::comparing`.
Copyright Louis Dionne 2013-2022
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/detail/decay.hpp>
#include <boost/hana/equal.hpp>
namespace boost { namespace hana {
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 detail::decay<F>::type>{static_cast<F&&>(f)};
}
//! @endcond
}} // end namespace boost::hana
#endif // !BOOST_HANA_COMPARING_HPP
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