ceph/src/boost/boost/hana/span.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::span`.
   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_SPAN_HPP
  11 #define BOOST_HANA_SPAN_HPP
  12
  13 #include <boost/hana/fwd/span.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/detail/nested_by.hpp> // required by fwd decl
  21 #include <boost/hana/detail/first_unsatisfied_index.hpp>
  22 #include <boost/hana/length.hpp>
  23 #include <boost/hana/pair.hpp>
  24 #include <boost/hana/unpack.hpp>
  25
  26 #include <cstddef>
  27 #include <utility>
  28
  29
  30 BOOST_HANA_NAMESPACE_BEGIN
  31     //! @cond
  32     template <typename Xs, typename Pred>
  33     constexpr auto span_t::operator()(Xs&& xs, Pred&& pred) const {
  34         using S = typename hana::tag_of<Xs>::type;
  35         using Span = BOOST_HANA_DISPATCH_IF(span_impl<S>,
  36             hana::Sequence<S>::value
  37         );
  38
  39     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  40         static_assert(hana::Sequence<S>::value,
  41         "hana::span(xs, pred) requires 'xs' to be a Sequence");
  42     #endif
  43
  44         return Span::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
  45     }
  46     //! @endcond
  47
  48     template <typename S, bool condition>
  49     struct span_impl<S, when<condition>> : default_ {
  50         template <typename Xs, std::size_t ...before, std::size_t ...after>
  51         static constexpr auto span_helper(Xs&& xs, std::index_sequence<before...>,
  52                                                    std::index_sequence<after...>)
  53         {
  54             return hana::make_pair(
  55                 hana::make<S>(hana::at_c<before>(static_cast<Xs&&>(xs))...),
  56                 hana::make<S>(hana::at_c<sizeof...(before) + after>(static_cast<Xs&&>(xs))...)
  57             );
  58         }
  59
  60         template <typename Xs, typename Pred>
  61         static constexpr auto apply(Xs&& xs, Pred&&) {
  62             using FirstUnsatisfied = decltype(
  63                 hana::unpack(static_cast<Xs&&>(xs),
  64                              detail::first_unsatisfied_index<Pred&&>{})
  65             );
  66             constexpr std::size_t breakpoint = FirstUnsatisfied::value;
  67             constexpr std::size_t N = decltype(hana::length(xs))::value;
  68             return span_helper(static_cast<Xs&&>(xs),
  69                                std::make_index_sequence<breakpoint>{},
  70                                std::make_index_sequence<N - breakpoint>{});
  71         }
  72     };
  73 BOOST_HANA_NAMESPACE_END
  74
  75 #endif // !BOOST_HANA_SPAN_HPP