ceph/src/boost/boost/hana/reverse.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::reverse`.
   4
   5 @copyright Louis Dionne 2013-2017
   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_REVERSE_HPP
  11 #define BOOST_HANA_REVERSE_HPP
  12
  13 #include <boost/hana/fwd/reverse.hpp>
  14
  15 #include <boost/hana/at.hpp>
  16 #include <boost/hana/concept/sequence.hpp>
  17 #include <boost/hana/config.hpp>
  18 #include <boost/hana/core/dispatch.hpp>
  19 #include <boost/hana/core/make.hpp>
  20 #include <boost/hana/length.hpp>
  21
  22 #include <cstddef>
  23 #include <utility>
  24
  25
  26 BOOST_HANA_NAMESPACE_BEGIN
  27     //! @cond
  28     template <typename Xs>
  29     constexpr auto reverse_t::operator()(Xs&& xs) const {
  30         using S = typename hana::tag_of<Xs>::type;
  31         using Reverse = BOOST_HANA_DISPATCH_IF(reverse_impl<S>,
  32             hana::Sequence<S>::value
  33         );
  34
  35     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  36         static_assert(hana::Sequence<S>::value,
  37         "hana::reverse(xs) requires 'xs' to be a Sequence");
  38     #endif
  39
  40         return Reverse::apply(static_cast<Xs&&>(xs));
  41     }
  42     //! @endcond
  43
  44     template <typename S, bool condition>
  45     struct reverse_impl<S, when<condition>> : default_ {
  46         template <typename Xs, std::size_t ...i>
  47         static constexpr auto reverse_helper(Xs&& xs, std::index_sequence<i...>) {
  48             return hana::make<S>(
  49                 hana::at_c<sizeof...(i) - i - 1>(static_cast<Xs&&>(xs))...
  50             );
  51         }
  52
  53         template <typename Xs>
  54         static constexpr auto apply(Xs&& xs) {
  55             constexpr std::size_t N = decltype(hana::length(xs))::value;
  56             return reverse_helper(static_cast<Xs&&>(xs), std::make_index_sequence<N>{});
  57         }
  58     };
  59 BOOST_HANA_NAMESPACE_END
  60
  61 #endif // !BOOST_HANA_REVERSE_HPP