63e88f80
 Hu Chunming
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/*!
@file
Defines `boost::hana::ordering`.
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_ORDERING_HPP
#define BOOST_HANA_ORDERING_HPP
#include <boost/hana/fwd/ordering.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/detail/decay.hpp>
#include <boost/hana/less.hpp>
namespace boost { namespace hana {
namespace detail {
template <typename F>
struct less_by {
F f;
template <typename X, typename Y>
constexpr decltype(auto) operator()(X&& x, Y&& y) const&
{ return hana::less(f(static_cast<X&&>(x)), f(static_cast<Y&&>(y))); }
template <typename X, typename Y>
constexpr decltype(auto) operator()(X&& x, Y&& y) &
{ return hana::less(f(static_cast<X&&>(x)), f(static_cast<Y&&>(y))); }
};
}
//! @cond
template <typename F>
constexpr auto ordering_t::operator()(F&& f) const {
return detail::less_by<typename detail::decay<F>::type>{static_cast<F&&>(f)};
}
//! @endcond
}} // end namespace boost::hana
#endif // !BOOST_HANA_ORDERING_HPP
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