ceph/src/boost/boost/hana/concat.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::concat`.
   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_CONCAT_HPP
  11 #define BOOST_HANA_CONCAT_HPP
  12
  13 #include <boost/hana/fwd/concat.hpp>
  14
  15 #include <boost/hana/at.hpp>
  16 #include <boost/hana/concept/monad_plus.hpp>
  17 #include <boost/hana/concept/sequence.hpp>
  18 #include <boost/hana/config.hpp>
  19 #include <boost/hana/core/dispatch.hpp>
  20 #include <boost/hana/core/make.hpp>
  21 #include <boost/hana/length.hpp>
  22
  23 #include <cstddef>
  24 #include <type_traits>
  25 #include <utility>
  26
  27
  28 BOOST_HANA_NAMESPACE_BEGIN
  29     //! @cond
  30     template <typename Xs, typename Ys>
  31     constexpr auto concat_t::operator()(Xs&& xs, Ys&& ys) const {
  32         using M = typename hana::tag_of<Xs>::type;
  33         using Concat = BOOST_HANA_DISPATCH_IF(concat_impl<M>,
  34             hana::MonadPlus<M>::value &&
  35             std::is_same<typename hana::tag_of<Ys>::type, M>::value
  36         );
  37
  38     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  39         static_assert(std::is_same<typename hana::tag_of<Ys>::type, M>::value,
  40         "hana::concat(xs, ys) requires 'xs' and 'ys' to have the same tag");
  41
  42         static_assert(hana::MonadPlus<M>::value,
  43         "hana::concat(xs, ys) requires 'xs' and 'ys' to be MonadPlus");
  44     #endif
  45
  46         return Concat::apply(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys));
  47     }
  48     //! @endcond
  49
  50     template <typename M, bool condition>
  51     struct concat_impl<M, when<condition>> : default_ {
  52         template <typename ...Args>
  53         static constexpr auto apply(Args&& ...) = delete;
  54     };
  55
  56     template <typename S>
  57     struct concat_impl<S, when<Sequence<S>::value>> {
  58         template <typename Xs, typename Ys, std::size_t ...xi, std::size_t ...yi>
  59         static constexpr auto
  60         concat_helper(Xs&& xs, Ys&& ys, std::index_sequence<xi...>,
  61                                         std::index_sequence<yi...>)
  62         {
  63             return hana::make<S>(
  64                 hana::at_c<xi>(static_cast<Xs&&>(xs))...,
  65                 hana::at_c<yi>(static_cast<Ys&&>(ys))...
  66             );
  67         }
  68
  69         template <typename Xs, typename Ys>
  70         static constexpr auto apply(Xs&& xs, Ys&& ys) {
  71             constexpr std::size_t xi = decltype(hana::length(xs))::value;
  72             constexpr std::size_t yi = decltype(hana::length(ys))::value;
  73             return concat_helper(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys),
  74                                  std::make_index_sequence<xi>{},
  75                                  std::make_index_sequence<yi>{});
  76         }
  77     };
  78 BOOST_HANA_NAMESPACE_END
  79
  80 #endif // !BOOST_HANA_CONCAT_HPP