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Diffstat (limited to 'boost/hana/maximum.hpp')
-rw-r--r-- | boost/hana/maximum.hpp | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/boost/hana/maximum.hpp b/boost/hana/maximum.hpp new file mode 100644 index 0000000000..36eaf1008d --- /dev/null +++ b/boost/hana/maximum.hpp @@ -0,0 +1,97 @@ +/*! +@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 |