ceph/src/boost/libs/hana/include/boost/hana/detail/unpack_flatten.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::detail::unpack_flatten`.
   4
   5 @copyright Louis Dionne 2013-2016
   6 Distributed under the Boost Software License, Version 1.0.
   7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   8  */
   9
  10 #ifndef BOOST_HANA_DETAIL_UNPACK_FLATTEN_HPP
  11 #define BOOST_HANA_DETAIL_UNPACK_FLATTEN_HPP
  12
  13 #include <boost/hana/at.hpp>
  14 #include <boost/hana/config.hpp>
  15 #include <boost/hana/detail/algorithm.hpp>
  16 #include <boost/hana/detail/array.hpp>
  17 #include <boost/hana/length.hpp>
  18 #include <boost/hana/unpack.hpp>
  19
  20 #include <cstddef>
  21 #include <utility>
  22
  23
  24 BOOST_HANA_NAMESPACE_BEGIN namespace detail {
  25     template <std::size_t ...Lengths>
  26     struct flatten_indices {
  27         // avoid empty arrays by appending 0 to `lengths`
  28         static constexpr std::size_t lengths[] = {Lengths..., 0};
  29         static constexpr auto flat_length =
  30             detail::accumulate(lengths, lengths + sizeof...(Lengths), 0);
  31
  32         template <bool Inner>
  33         static constexpr auto compute() {
  34             detail::array<std::size_t, flat_length> indices{};
  35             for (std::size_t index = 0, i = 0; i < sizeof...(Lengths); ++i)
  36                 for (std::size_t j = 0; j < lengths[i]; ++j, ++index)
  37                     indices[index] = (Inner ? i : j);
  38             return indices;
  39         }
  40
  41         static constexpr auto inner = compute<true>();
  42         static constexpr auto outer = compute<false>();
  43
  44         template <typename Xs, typename F, std::size_t ...i>
  45         static constexpr decltype(auto)
  46         apply(Xs&& xs, F&& f, std::index_sequence<i...>) {
  47             return static_cast<F&&>(f)(
  48                 hana::at_c<outer[i]>(hana::at_c<inner[i]>(
  49                     static_cast<Xs&&>(xs)
  50                 ))...
  51             );
  52         }
  53     };
  54
  55     struct make_flatten_indices {
  56         template <typename ...Xs>
  57         auto operator()(Xs const& ...xs) const -> detail::flatten_indices<
  58             decltype(hana::length(xs))::value...
  59         >;
  60     };
  61
  62     template <typename Xs, typename F>
  63     constexpr decltype(auto) unpack_flatten(Xs&& xs, F&& f) {
  64         using Indices = decltype(hana::unpack(xs, make_flatten_indices{}));
  65         return Indices::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f),
  66                         std::make_index_sequence<Indices::flat_length>{});
  67     }
  68 } BOOST_HANA_NAMESPACE_END
  69
  70 #endif // !BOOST_HANA_DETAIL_UNPACK_FLATTEN_HPP