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/*!
@file
Defines `boost::hana::fold_right`.
@copyright Louis Dionne 2013-2017
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_FOLD_RIGHT_HPP
#define BOOST_HANA_FOLD_RIGHT_HPP
#include <boost/hana/fwd/fold_right.hpp>
#include <boost/hana/concept/foldable.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/detail/variadic/foldr1.hpp>
#include <boost/hana/functional/partial.hpp>
#include <boost/hana/fwd/unpack.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template <typename Xs, typename State, typename F>
constexpr decltype(auto) fold_right_t::operator()(Xs&& xs, State&& state, F&& f) const {
using S = typename hana::tag_of<Xs>::type;
using FoldRight = BOOST_HANA_DISPATCH_IF(fold_right_impl<S>,
hana::Foldable<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Foldable<S>::value,
"hana::fold_right(xs, state, f) requires 'xs' to be Foldable");
#endif
return FoldRight::apply(static_cast<Xs&&>(xs),
static_cast<State&&>(state),
static_cast<F&&>(f));
}
template <typename Xs, typename F>
constexpr decltype(auto) fold_right_t::operator()(Xs&& xs, F&& f) const {
using S = typename hana::tag_of<Xs>::type;
using FoldRight = BOOST_HANA_DISPATCH_IF(fold_right_impl<S>,
hana::Foldable<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Foldable<S>::value,
"hana::fold_right(xs, f) requires 'xs' to be Foldable");
#endif
return FoldRight::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f));
}
//! @endcond
namespace detail {
template <typename F, typename State>
struct variadic_foldr {
F& f;
State& state;
template <typename ...T>
constexpr decltype(auto) operator()(T&& ...t) const {
return detail::variadic::foldr(
static_cast<F&&>(f),
static_cast<State&&>(state),
static_cast<T&&>(t)...
);
}
};
}
template <typename T, bool condition>
struct fold_right_impl<T, when<condition>> : default_ {
// with state
template <typename Xs, typename S, typename F>
static constexpr decltype(auto) apply(Xs&& xs, S&& s, F&& f) {
return hana::unpack(static_cast<Xs&&>(xs),
detail::variadic_foldr<F, S>{f, s}
);
}
// without state
template <typename Xs, typename F>
static constexpr decltype(auto) apply(Xs&& xs, F&& f) {
return hana::unpack(static_cast<Xs&&>(xs),
hana::partial(
detail::variadic::foldr1,
static_cast<F&&>(f)
)
);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FOLD_RIGHT_HPP
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