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