598bfd3f
 Hu Chunming
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/*!
@file
Defines `boost::hana::maximum`.
Copyright Louis Dionne 2013-2022
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>
namespace boost { namespace hana {
//! @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); }
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_MAXIMUM_HPP
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