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 Hu Chunming
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/*!
@file
Defines `boost::hana::scan_right`.
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_SCAN_RIGHT_HPP
#define BOOST_HANA_SCAN_RIGHT_HPP
#include <boost/hana/fwd/scan_right.hpp>
#include <boost/hana/at.hpp>
#include <boost/hana/concept/sequence.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/core/make.hpp>
#include <boost/hana/empty.hpp>
#include <boost/hana/front.hpp>
#include <boost/hana/length.hpp>
#include <boost/hana/prepend.hpp>
#include <cstddef>
#include <utility>
namespace boost { namespace hana {
//! @cond
template <typename Xs, typename F>
constexpr auto scan_right_t::operator()(Xs&& xs, F const& f) const {
using S = typename hana::tag_of<Xs>::type;
using ScanRight = BOOST_HANA_DISPATCH_IF(scan_right_impl<S>,
hana::Sequence<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::scan_right(xs, f) requires 'xs' to be a Sequence");
#endif
return ScanRight::apply(static_cast<Xs&&>(xs), f);
}
template <typename Xs, typename State, typename F>
constexpr auto scan_right_t::operator()(Xs&& xs, State&& state, F const& f) const {
using S = typename hana::tag_of<Xs>::type;
using ScanRight = BOOST_HANA_DISPATCH_IF(scan_right_impl<S>,
hana::Sequence<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::scan_right(xs, state, f) requires 'xs' to be a Sequence");
#endif
return ScanRight::apply(static_cast<Xs&&>(xs),
static_cast<State&&>(state), f);
}
//! @endcond
template <typename S, bool condition>
struct scan_right_impl<S, when<condition>> : default_ {
// Without initial state
template <typename Xs, typename F, std::size_t n1, std::size_t n2, std::size_t ...ns>
static constexpr auto
apply1_impl(Xs&& xs, F const& f, std::index_sequence<n1, n2, ns...>) {
auto rest = scan_right_impl::apply1_impl(static_cast<Xs&&>(xs),
f, std::index_sequence<n2, ns...>{});
auto element = f(hana::at_c<n1>(static_cast<Xs&&>(xs)), hana::front(rest));
return hana::prepend(std::move(rest), std::move(element));
}
template <typename Xs, typename F, std::size_t n>
static constexpr auto apply1_impl(Xs&& xs, F const&, std::index_sequence<n>) {
return hana::make<S>(hana::at_c<n>(static_cast<Xs&&>(xs)));
}
template <typename Xs, typename F>
static constexpr auto apply1_impl(Xs&&, F const&, std::index_sequence<>) {
return hana::empty<S>();
}
template <typename Xs, typename F>
static constexpr auto apply(Xs&& xs, F const& f) {
constexpr std::size_t Len = decltype(hana::length(xs))::value;
return scan_right_impl::apply1_impl(static_cast<Xs&&>(xs),
f, std::make_index_sequence<Len>{});
}
// With initial state
template <typename Xs, typename State, typename F,
std::size_t n1, std::size_t n2, std::size_t ...ns>
static constexpr auto
apply_impl(Xs&& xs, State&& state, F const& f,
std::index_sequence<n1, n2, ns...>)
{
auto rest = scan_right_impl::apply_impl(static_cast<Xs&&>(xs),
static_cast<State&&>(state),
f, std::index_sequence<n2, ns...>{});
auto element = f(hana::at_c<n1>(static_cast<Xs&&>(xs)), hana::front(rest));
return hana::prepend(std::move(rest), std::move(element));
}
template <typename Xs, typename State, typename F, std::size_t n>
static constexpr auto
apply_impl(Xs&& xs, State&& state, F const& f, std::index_sequence<n>) {
auto element = f(hana::at_c<n>(static_cast<Xs&&>(xs)), state);
return hana::make<S>(std::move(element), static_cast<State&&>(state));
}
template <typename Xs, typename State, typename F>
static constexpr auto
apply_impl(Xs&&, State&& state, F const&, std::index_sequence<>) {
return hana::make<S>(static_cast<State&&>(state));
}
template <typename Xs, typename State, typename F>
static constexpr auto apply(Xs&& xs, State&& state, F const& f) {
constexpr std::size_t Len = decltype(hana::length(xs))::value;
return scan_right_impl::apply_impl(static_cast<Xs&&>(xs),
static_cast<State&&>(state),
f, std::make_index_sequence<Len>{});
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_SCAN_RIGHT_HPP
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