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 Hu Chunming
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/*!
@file
Defines `boost::hana::greater`.
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_GREATER_HPP
#define BOOST_HANA_GREATER_HPP
#include <boost/hana/fwd/greater.hpp>
#include <boost/hana/concept/orderable.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/common.hpp>
#include <boost/hana/core/to.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/detail/concepts.hpp>
#include <boost/hana/detail/has_common_embedding.hpp>
#include <boost/hana/detail/nested_than.hpp> // required by fwd decl
#include <boost/hana/if.hpp>
namespace boost { namespace hana {
//! @cond
template <typename X, typename Y>
constexpr decltype(auto) greater_t::operator()(X&& x, Y&& y) const {
using T = typename hana::tag_of<X>::type;
using U = typename hana::tag_of<Y>::type;
using Greater = BOOST_HANA_DISPATCH_IF(decltype(greater_impl<T, U>{}),
hana::Orderable<T>::value &&
hana::Orderable<U>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Orderable<T>::value,
"hana::greater(x, y) requires 'x' to be Orderable");
static_assert(hana::Orderable<U>::value,
"hana::greater(x, y) requires 'y' to be Orderable");
#endif
return Greater::apply(static_cast<X&&>(x), static_cast<Y&&>(y));
}
//! @endcond
template <typename T, typename U, bool condition>
struct greater_impl<T, U, when<condition>> : default_ {
template <typename X, typename Y>
static constexpr decltype(auto) apply(X&& x, Y&& y) {
return hana::less(static_cast<Y&&>(y),
static_cast<X&&>(x));
}
};
// Cross-type overload
template <typename T, typename U>
struct greater_impl<T, U, when<
detail::has_nontrivial_common_embedding<Orderable, T, U>::value
>> {
using C = typename hana::common<T, U>::type;
template <typename X, typename Y>
static constexpr decltype(auto) apply(X&& x, Y&& y) {
return hana::greater(hana::to<C>(static_cast<X&&>(x)),
hana::to<C>(static_cast<Y&&>(y)));
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_GREATER_HPP
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