72 lines
2.4 KiB
C++
72 lines
2.4 KiB
C++
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/*!
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@file
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Defines `boost::hana::greater`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_GREATER_HPP
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#define BOOST_HANA_GREATER_HPP
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#include <boost/hana/fwd/greater.hpp>
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#include <boost/hana/concept/orderable.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/common.hpp>
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#include <boost/hana/core/to.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/detail/concepts.hpp>
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#include <boost/hana/detail/has_common_embedding.hpp>
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#include <boost/hana/detail/nested_than.hpp> // required by fwd decl
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#include <boost/hana/if.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename X, typename Y>
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constexpr decltype(auto) greater_t::operator()(X&& x, Y&& y) const {
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using T = typename hana::tag_of<X>::type;
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using U = typename hana::tag_of<Y>::type;
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using Greater = BOOST_HANA_DISPATCH_IF(decltype(greater_impl<T, U>{}),
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hana::Orderable<T>::value &&
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hana::Orderable<U>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Orderable<T>::value,
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"hana::greater(x, y) requires 'x' to be Orderable");
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static_assert(hana::Orderable<U>::value,
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"hana::greater(x, y) requires 'y' to be Orderable");
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#endif
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return Greater::apply(static_cast<X&&>(x), static_cast<Y&&>(y));
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}
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//! @endcond
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template <typename T, typename U, bool condition>
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struct greater_impl<T, U, when<condition>> : default_ {
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template <typename X, typename Y>
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static constexpr decltype(auto) apply(X&& x, Y&& y) {
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return hana::less(static_cast<Y&&>(y),
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static_cast<X&&>(x));
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}
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};
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// Cross-type overload
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template <typename T, typename U>
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struct greater_impl<T, U, when<
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detail::has_nontrivial_common_embedding<Orderable, T, U>::value
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>> {
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using C = typename hana::common<T, U>::type;
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template <typename X, typename Y>
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static constexpr decltype(auto) apply(X&& x, Y&& y) {
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return hana::greater(hana::to<C>(static_cast<X&&>(x)),
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hana::to<C>(static_cast<Y&&>(y)));
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_GREATER_HPP
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