ceph/src/boost/boost/hana/unfold_right.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::unfold_right`.
   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_UNFOLD_RIGHT_HPP
  11 #define BOOST_HANA_UNFOLD_RIGHT_HPP
  12
  13 #include <boost/hana/fwd/unfold_right.hpp>
  14
  15 #include <boost/hana/concept/sequence.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/dispatch.hpp>
  18 #include <boost/hana/empty.hpp>
  19 #include <boost/hana/first.hpp>
  20 #include <boost/hana/functional/partial.hpp>
  21 #include <boost/hana/optional.hpp>
  22 #include <boost/hana/prepend.hpp>
  23 #include <boost/hana/second.hpp>
  24
  25
  26 BOOST_HANA_NAMESPACE_BEGIN
  27     //! @cond
  28     template <typename S>
  29     struct unfold_right_t {
  30     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  31         static_assert(hana::Sequence<S>::value,
  32         "hana::unfold_right<S> requires 'S' to be a Sequence");
  33     #endif
  34
  35         template <typename State, typename F>
  36         constexpr auto operator()(State&& state, F&& f) const {
  37             return unfold_right_impl<S>::apply(
  38                 static_cast<State&&>(state),
  39                 static_cast<F&&>(f)
  40             );
  41         }
  42     };
  43     //! @endcond
  44
  45     template <typename S, bool condition>
  46     struct unfold_right_impl<S, when<condition>> : default_ {
  47         struct unfold_right_helper {
  48             template <typename F, typename P>
  49             constexpr auto operator()(F&& f, P&& p) const {
  50                 return hana::prepend(
  51                     unfold_right_impl::apply(
  52                         hana::second(static_cast<P&&>(p)),
  53                         static_cast<F&&>(f)
  54                     ),
  55                     hana::first(static_cast<P&&>(p))
  56                 );
  57             }
  58         };
  59
  60         template <typename Init, typename F>
  61         static constexpr auto apply(Init&& init, F&& f) {
  62             decltype(auto) elt = f(static_cast<Init&&>(init));
  63             return hana::maybe(hana::empty<S>(),
  64                 hana::partial(unfold_right_helper{}, static_cast<F&&>(f)),
  65                 static_cast<decltype(elt)&&>(elt)
  66             );
  67         }
  68     };
  69 BOOST_HANA_NAMESPACE_END
  70
  71 #endif // !BOOST_HANA_UNFOLD_RIGHT_HPP