71 lines
2.4 KiB
C++
71 lines
2.4 KiB
C++
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/*!
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@file
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Defines `boost::hana::detail::unpack_flatten`.
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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_DETAIL_UNPACK_FLATTEN_HPP
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#define BOOST_HANA_DETAIL_UNPACK_FLATTEN_HPP
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#include <boost/hana/at.hpp>
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#include <boost/hana/config.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/length.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 namespace detail {
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template <std::size_t ...Lengths>
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struct flatten_indices {
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// avoid empty arrays by appending 0 to `lengths`
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static constexpr std::size_t lengths[] = {Lengths..., 0};
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static constexpr auto flat_length =
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detail::accumulate(lengths, lengths + sizeof...(Lengths), 0);
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template <bool Inner>
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static constexpr auto compute() {
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detail::array<std::size_t, flat_length> indices{};
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for (std::size_t index = 0, i = 0; i < sizeof...(Lengths); ++i)
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for (std::size_t j = 0; j < lengths[i]; ++j, ++index)
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indices[index] = (Inner ? i : j);
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return indices;
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}
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static constexpr auto inner = compute<true>();
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static constexpr auto outer = compute<false>();
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template <typename Xs, typename F, std::size_t ...i>
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static constexpr decltype(auto)
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apply(Xs&& xs, F&& f, std::index_sequence<i...>) {
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return static_cast<F&&>(f)(
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hana::at_c<outer[i]>(hana::at_c<inner[i]>(
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static_cast<Xs&&>(xs)
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))...
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);
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}
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};
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struct make_flatten_indices {
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template <typename ...Xs>
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auto operator()(Xs const& ...xs) const -> detail::flatten_indices<
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decltype(hana::length(xs))::value...
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>;
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};
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template <typename Xs, typename F>
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constexpr decltype(auto) unpack_flatten(Xs&& xs, F&& f) {
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using Indices = decltype(hana::unpack(xs, make_flatten_indices{}));
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return Indices::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f),
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std::make_index_sequence<Indices::flat_length>{});
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}
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} BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_DETAIL_UNPACK_FLATTEN_HPP
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