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+/*!
+@file
+Defines `boost::hana::greater`.
+
+@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_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>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ //! @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)));
+ }
+ };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_GREATER_HPP