/*! @file Defines `boost::hana::group`. @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_GROUP_HPP #define BOOST_HANA_GROUP_HPP #include <boost/hana/fwd/group.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/detail/algorithm.hpp> #include <boost/hana/detail/array.hpp> #include <boost/hana/detail/nested_by.hpp> // required by fwd decl #include <boost/hana/equal.hpp> #include <boost/hana/length.hpp> #include <cstddef> #include <utility> BOOST_HANA_NAMESPACE_BEGIN //! @cond template <typename Xs> constexpr auto group_t::operator()(Xs&& xs) const { using S = typename hana::tag_of<Xs>::type; using Group = BOOST_HANA_DISPATCH_IF(group_impl<S>, hana::Sequence<S>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::Sequence<S>::value, "hana::group(xs) requires 'xs' to be a Sequence"); #endif return Group::apply(static_cast<Xs&&>(xs)); } template <typename Xs, typename Predicate> constexpr auto group_t::operator()(Xs&& xs, Predicate&& pred) const { using S = typename hana::tag_of<Xs>::type; using Group = BOOST_HANA_DISPATCH_IF(group_impl<S>, hana::Sequence<S>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::Sequence<S>::value, "hana::group(xs, predicate) requires 'xs' to be a Sequence"); #endif return Group::apply(static_cast<Xs&&>(xs), static_cast<Predicate&&>(pred)); } //! @endcond namespace detail { template <typename Xs, std::size_t ...i> constexpr auto get_subsequence_(Xs&& xs, std::index_sequence<i...>) { using S = typename hana::tag_of<Xs>::type; return hana::make<S>(hana::at_c<i>(static_cast<Xs&&>(xs))...); } template <std::size_t offset, typename Indices> struct offset_by; template <std::size_t offset, std::size_t ...i> struct offset_by<offset, std::index_sequence<i...>> { using type = std::index_sequence<(offset + i)...>; }; template <bool ...b> struct group_indices { static constexpr bool bs[sizeof...(b)] = {b...}; static constexpr std::size_t n_groups = detail::count(bs, bs + sizeof(bs), false) + 1; static constexpr auto compute_info() { detail::array<std::size_t, n_groups> sizes{}, offsets{}; for (std::size_t g = 0, i = 0, offset = 0; g < n_groups; ++g) { offsets[g] = offset; sizes[g] = 1; while (i < sizeof...(b) && bs[i++]) ++sizes[g]; offset += sizes[g]; } return std::make_pair(offsets, sizes); } static constexpr auto info = compute_info(); static constexpr auto group_offsets = info.first; static constexpr auto group_sizes = info.second; template <typename S, typename Xs, std::size_t ...i> static constexpr auto finish(Xs&& xs, std::index_sequence<i...>) { return hana::make<S>( detail::get_subsequence_( static_cast<Xs&&>(xs), typename offset_by< group_offsets[i], std::make_index_sequence<group_sizes[i]> >::type{} )... ); } }; } // end namespace detail template <typename S, bool condition> struct group_impl<S, when<condition>> : default_ { template <typename Xs, typename Pred, std::size_t ...i> static constexpr auto group_helper(Xs&& xs, Pred&& pred, std::index_sequence<0, i...>) { using info = detail::group_indices<static_cast<bool>(decltype( pred(hana::at_c<i - 1>(static_cast<Xs&&>(xs)), hana::at_c<i>(static_cast<Xs&&>(xs))) )::value)...>; return info::template finish<S>(static_cast<Xs&&>(xs), std::make_index_sequence<info::n_groups>{} ); } template <typename Xs, typename Pred> static constexpr auto group_helper(Xs&& xs, Pred&&, std::index_sequence<0>) { return hana::make<S>(static_cast<Xs&&>(xs)); } template <typename Xs, typename Pred> static constexpr auto group_helper(Xs&&, Pred&&, std::index_sequence<>) { return hana::make<S>(); } template <typename Xs, typename Pred> static constexpr auto apply(Xs&& xs, Pred&& pred) { constexpr std::size_t len = decltype(hana::length(xs))::value; return group_helper(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred), std::make_index_sequence<len>{}); } template <typename Xs> static constexpr auto apply(Xs&& xs) { return group_impl::apply(static_cast<Xs&&>(xs), hana::equal); } }; BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_GROUP_HPP