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134 lines
5.1 KiB
C++
134 lines
5.1 KiB
C++
/*!
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@file
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Defines `boost::hana::scan_left`.
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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_SCAN_LEFT_HPP
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#define BOOST_HANA_SCAN_LEFT_HPP
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#include <boost/hana/fwd/scan_left.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/concept/sequence.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/core/make.hpp>
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#include <boost/hana/empty.hpp>
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#include <boost/hana/length.hpp>
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#include <boost/hana/prepend.hpp>
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#include <cstddef>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename F>
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constexpr auto scan_left_t::operator()(Xs&& xs, F const& f) const {
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using S = typename hana::tag_of<Xs>::type;
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using ScanLeft = BOOST_HANA_DISPATCH_IF(scan_left_impl<S>,
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hana::Sequence<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Sequence<S>::value,
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"hana::scan_left(xs, f) requires 'xs' to be a Sequence");
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#endif
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return ScanLeft::apply(static_cast<Xs&&>(xs), f);
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}
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template <typename Xs, typename State, typename F>
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constexpr auto scan_left_t::operator()(Xs&& xs, State&& state, F const& f) const {
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using S = typename hana::tag_of<Xs>::type;
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using ScanLeft = BOOST_HANA_DISPATCH_IF(scan_left_impl<S>,
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hana::Sequence<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Sequence<S>::value,
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"hana::scan_left(xs, state, f) requires 'xs' to be a Sequence");
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#endif
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return ScanLeft::apply(static_cast<Xs&&>(xs),
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static_cast<State&&>(state), f);
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}
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//! @endcond
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template <typename S, bool condition>
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struct scan_left_impl<S, when<condition>> : default_ {
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// Without initial state
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template <typename Xs, typename F, std::size_t n1, std::size_t n2, std::size_t ...ns>
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static constexpr auto
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apply1_impl(Xs&& xs, F const& f, std::index_sequence<n1, n2, ns...>) {
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static_assert(n1 == 0, "logic error in Boost.Hana: file a bug report");
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// Use scan_left with the first element as an initial state.
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return scan_left_impl::apply_impl(
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static_cast<Xs&&>(xs),
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hana::at_c<0>(static_cast<Xs&&>(xs)),
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f, std::index_sequence<n2, ns...>{}
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);
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}
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template <typename Xs, typename F, std::size_t n>
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static constexpr auto apply1_impl(Xs&& xs, F const&, std::index_sequence<n>) {
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return hana::make<S>(hana::at_c<n>(static_cast<Xs&&>(xs)));
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}
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template <typename Xs, typename F>
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static constexpr auto apply1_impl(Xs&&, F const&, std::index_sequence<>) {
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return hana::empty<S>();
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}
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template <typename Xs, typename F>
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static constexpr auto apply(Xs&& xs, F const& f) {
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constexpr std::size_t Len = decltype(hana::length(xs))::value;
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return scan_left_impl::apply1_impl(static_cast<Xs&&>(xs),
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f, std::make_index_sequence<Len>{});
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}
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// With initial state
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template <typename Xs, typename State, typename F,
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std::size_t n1, std::size_t n2, std::size_t ...ns>
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static constexpr auto
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apply_impl(Xs&& xs, State&& state, F const& f,
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std::index_sequence<n1, n2, ns...>)
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{
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auto rest = scan_left_impl::apply_impl(
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static_cast<Xs&&>(xs),
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f(state, hana::at_c<n1>(static_cast<Xs&&>(xs))),
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f, std::index_sequence<n2, ns...>{});
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return hana::prepend(std::move(rest), static_cast<State&&>(state));
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}
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template <typename Xs, typename State, typename F, std::size_t n>
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static constexpr auto
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apply_impl(Xs&& xs, State&& state, F const& f, std::index_sequence<n>) {
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auto new_state = f(state, hana::at_c<n>(static_cast<Xs&&>(xs)));
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return hana::make<S>(static_cast<State&&>(state), std::move(new_state));
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}
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template <typename Xs, typename State, typename F>
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static constexpr auto
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apply_impl(Xs&&, State&& state, F const&, std::index_sequence<>) {
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return hana::make<S>(static_cast<State&&>(state));
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}
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template <typename Xs, typename State, typename F>
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static constexpr auto apply(Xs&& xs, State&& state, F const& f) {
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constexpr std::size_t Len = decltype(hana::length(xs))::value;
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return scan_left_impl::apply_impl(static_cast<Xs&&>(xs),
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static_cast<State&&>(state),
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f, std::make_index_sequence<Len>{});
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_SCAN_LEFT_HPP
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