117 lines
4.2 KiB
C++
117 lines
4.2 KiB
C++
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/*!
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@file
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Defines `boost::hana::partition`.
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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_PARTITION_HPP
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#define BOOST_HANA_PARTITION_HPP
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#include <boost/hana/fwd/partition.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/detail/algorithm.hpp>
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#include <boost/hana/detail/array.hpp>
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#include <boost/hana/detail/decay.hpp>
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#include <boost/hana/detail/nested_by.hpp> // required by fwd decl
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#include <boost/hana/pair.hpp>
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#include <boost/hana/unpack.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 Pred>
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constexpr auto partition_t::operator()(Xs&& xs, Pred&& pred) const {
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using S = typename hana::tag_of<Xs>::type;
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using Partition = BOOST_HANA_DISPATCH_IF(partition_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::partition(xs, pred) requires 'xs' to be a Sequence");
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#endif
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return Partition::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
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}
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//! @endcond
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namespace detail {
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template <bool ...B>
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struct partition_indices {
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static constexpr bool results[] = {B..., false}; // avoid empty array
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static constexpr std::size_t left_size =
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detail::count(results, results + sizeof...(B), true);
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static constexpr std::size_t right_size = sizeof...(B) - left_size;
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static constexpr auto compute_left() {
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detail::array<std::size_t, left_size> indices{};
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std::size_t* left = &indices[0];
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for (std::size_t i = 0; i < sizeof...(B); ++i)
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if (results[i])
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*left++ = i;
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return indices;
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}
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static constexpr auto compute_right() {
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detail::array<std::size_t, right_size> indices{};
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std::size_t* right = &indices[0];
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for (std::size_t i = 0; i < sizeof...(B); ++i)
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if (!results[i])
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*right++ = i;
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return indices;
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}
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static constexpr auto left = compute_left();
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static constexpr auto right = compute_right();
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template <typename S, typename Xs, std::size_t ...l, std::size_t ...r>
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static constexpr auto apply(Xs&& xs, std::index_sequence<l...>,
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std::index_sequence<r...>)
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{
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return hana::make<hana::pair_tag>(
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hana::make<S>(hana::at_c<left[l]>(static_cast<Xs&&>(xs))...),
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hana::make<S>(hana::at_c<right[r]>(static_cast<Xs&&>(xs))...)
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);
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}
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};
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template <typename Pred>
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struct deduce_partition_indices {
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template <typename ...Xs>
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auto operator()(Xs&& ...xs) const -> detail::partition_indices<
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static_cast<bool>(detail::decay<
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decltype(std::declval<Pred>()(static_cast<Xs&&>(xs)))
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>::type::value)...
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> { return {}; }
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};
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}
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template <typename S, bool condition>
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struct partition_impl<S, when<condition>> : default_ {
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template <typename Xs, typename Pred>
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static constexpr auto apply(Xs&& xs, Pred&&) {
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using Indices = decltype(hana::unpack(
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static_cast<Xs&&>(xs), detail::deduce_partition_indices<Pred&&>{}
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));
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return Indices::template apply<S>(
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static_cast<Xs&&>(xs),
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std::make_index_sequence<Indices::left_size>{},
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std::make_index_sequence<Indices::right_size>{}
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);
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_PARTITION_HPP
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