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+/*!
+@file
+Defines `boost::hana::maximum`.
+
+@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_MAXIMUM_HPP
+#define BOOST_HANA_MAXIMUM_HPP
+
+#include <boost/hana/fwd/maximum.hpp>
+
+#include <boost/hana/concept/foldable.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/detail/nested_by.hpp> // required by fwd decl
+#include <boost/hana/fold_left.hpp>
+#include <boost/hana/if.hpp>
+#include <boost/hana/less.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ //! @cond
+ template <typename Xs>
+ constexpr decltype(auto) maximum_t::operator()(Xs&& xs) const {
+ using S = typename hana::tag_of<Xs>::type;
+ using Maximum = BOOST_HANA_DISPATCH_IF(maximum_impl<S>,
+ hana::Foldable<S>::value
+ );
+
+ #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+ static_assert(hana::Foldable<S>::value,
+ "hana::maximum(xs) requires 'xs' to be Foldable");
+ #endif
+
+ return Maximum::apply(static_cast<Xs&&>(xs));
+ }
+
+ template <typename Xs, typename Predicate>
+ constexpr decltype(auto) maximum_t::operator()(Xs&& xs, Predicate&& pred) const {
+ using S = typename hana::tag_of<Xs>::type;
+ using Maximum = BOOST_HANA_DISPATCH_IF(maximum_pred_impl<S>,
+ hana::Foldable<S>::value
+ );
+
+ #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+ static_assert(hana::Foldable<S>::value,
+ "hana::maximum(xs, predicate) requires 'xs' to be Foldable");
+ #endif
+
+ return Maximum::apply(static_cast<Xs&&>(xs),
+ static_cast<Predicate&&>(pred));
+ }
+ //! @endcond
+
+ //////////////////////////////////////////////////////////////////////////
+ // maximum (with a custom predicate)
+ //////////////////////////////////////////////////////////////////////////
+ namespace detail {
+ template <typename Pred>
+ struct max_by {
+ Pred pred;
+
+ template <typename X, typename Y>
+ constexpr decltype(auto) operator()(X&& x, Y&& y) const {
+ auto result = (*pred)(x, y);
+ return hana::if_(result, static_cast<Y&&>(y),
+ static_cast<X&&>(x));
+ }
+ };
+ }
+
+ template <typename T, bool condition>
+ struct maximum_pred_impl<T, when<condition>> : default_ {
+ template <typename Xs, typename Pred>
+ static constexpr decltype(auto) apply(Xs&& xs, Pred&& pred) {
+ // We use a pointer instead of a reference to avoid a Clang ICE.
+ return hana::fold_left(static_cast<Xs&&>(xs),
+ detail::max_by<decltype(&pred)>{&pred}
+ );
+ }
+ };
+
+ //////////////////////////////////////////////////////////////////////////
+ // maximum (without a custom predicate)
+ //////////////////////////////////////////////////////////////////////////
+ template <typename T, bool condition>
+ struct maximum_impl<T, when<condition>> : default_ {
+ template <typename Xs>
+ static constexpr decltype(auto) apply(Xs&& xs)
+ { return hana::maximum(static_cast<Xs&&>(xs), hana::less); }
+ };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_MAXIMUM_HPP