ceph/src/boost/libs/hana/include/boost/hana/intersperse.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::intersperse`.
   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_INTERSPERSE_HPP
  11 #define BOOST_HANA_INTERSPERSE_HPP
  12
  13 #include <boost/hana/fwd/intersperse.hpp>
  14
  15 #include <boost/hana/at.hpp>
  16 #include <boost/hana/bool.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 <utility>
  25
  26
  27 BOOST_HANA_NAMESPACE_BEGIN
  28     //! @cond
  29     template <typename Xs, typename Z>
  30     constexpr auto intersperse_t::operator()(Xs&& xs, Z&& z) const {
  31         using S = typename hana::tag_of<Xs>::type;
  32         using Intersperse = BOOST_HANA_DISPATCH_IF(intersperse_impl<S>,
  33             hana::Sequence<S>::value
  34         );
  35
  36     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  37         static_assert(hana::Sequence<S>::value,
  38         "hana::intersperse(xs, z) requires 'xs' to be a Sequence");
  39     #endif
  40
  41         return Intersperse::apply(static_cast<Xs&&>(xs), static_cast<Z&&>(z));
  42     }
  43     //! @endcond
  44
  45     template <typename S, bool condition>
  46     struct intersperse_impl<S, when<condition>> : default_ {
  47         template <std::size_t i, typename Xs, typename Z>
  48         static constexpr decltype(auto)
  49         pick(Xs&&, Z&& z, hana::false_ /* odd index */)
  50         { return static_cast<Z&&>(z); }
  51
  52         template <std::size_t i, typename Xs, typename Z>
  53         static constexpr decltype(auto)
  54         pick(Xs&& xs, Z&&, hana::true_ /* even index */)
  55         { return hana::at_c<(i + 1) / 2>(static_cast<Xs&&>(xs)); }
  56
  57         template <typename Xs, typename Z, std::size_t ...i>
  58         static constexpr auto
  59         intersperse_helper(Xs&& xs, Z&& z, std::index_sequence<i...>) {
  60             return hana::make<S>(
  61                 pick<i>(static_cast<Xs&&>(xs), static_cast<Z&&>(z),
  62                         hana::bool_c<(i % 2 == 0)>)...
  63             );
  64         }
  65
  66         template <typename Xs, typename Z>
  67         static constexpr auto apply(Xs&& xs, Z&& z) {
  68             constexpr std::size_t size = decltype(hana::length(xs))::value;
  69             constexpr std::size_t new_size = size == 0 ? 0 : (size * 2) - 1;
  70             return intersperse_helper(static_cast<Xs&&>(xs), static_cast<Z&&>(z),
  71                                       std::make_index_sequence<new_size>{});
  72         }
  73     };
  74 BOOST_HANA_NAMESPACE_END
  75
  76 #endif // !BOOST_HANA_INTERSPERSE_HPP