boost/hana/sort.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::sort`.
   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_SORT_HPP
  11 #define BOOST_HANA_SORT_HPP
  12
  13 #include <boost/hana/fwd/sort.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/length.hpp>
  22 #include <boost/hana/less.hpp>
  23
  24 #include <utility> // std::declval, std::index_sequence
  25
  26
  27 BOOST_HANA_NAMESPACE_BEGIN
  28     //! @cond
  29     template <typename Xs, typename Predicate>
  30     constexpr auto sort_t::operator()(Xs&& xs, Predicate&& pred) const {
  31         using S = typename hana::tag_of<Xs>::type;
  32         using Sort = BOOST_HANA_DISPATCH_IF(sort_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::sort(xs, predicate) requires 'xs' to be a Sequence");
  39     #endif
  40
  41         return Sort::apply(static_cast<Xs&&>(xs),
  42                            static_cast<Predicate&&>(pred));
  43     }
  44
  45     template <typename Xs>
  46     constexpr auto sort_t::operator()(Xs&& xs) const {
  47         using S = typename hana::tag_of<Xs>::type;
  48         using Sort = BOOST_HANA_DISPATCH_IF(sort_impl<S>,
  49             hana::Sequence<S>::value
  50         );
  51
  52     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  53         static_assert(hana::Sequence<S>::value,
  54         "hana::sort(xs) requires 'xs' to be a Sequence");
  55     #endif
  56
  57         return Sort::apply(static_cast<Xs&&>(xs));
  58     }
  59     //! @endcond
  60
  61     namespace detail {
  62         template <typename Xs, typename Pred>
  63         struct sort_predicate {
  64             template <std::size_t I, std::size_t J>
  65             using apply = decltype(std::declval<Pred>()(
  66                 hana::at_c<I>(std::declval<Xs>()),
  67                 hana::at_c<J>(std::declval<Xs>())
  68             ));
  69         };
  70
  71         template <typename Pred, std::size_t Insert, bool IsInsertionPoint,
  72                   typename Left,
  73                   std::size_t ...Right>
  74         struct insert;
  75
  76         // We did not find the insertion point; continue processing elements
  77         // recursively.
  78         template <
  79             typename Pred, std::size_t Insert,
  80             std::size_t ...Left,
  81             std::size_t Right1, std::size_t Right2, std::size_t ...Right
  82         >
  83         struct insert<Pred, Insert, false,
  84                       std::index_sequence<Left...>,
  85                       Right1, Right2, Right...
  86         > {
  87             using type = typename insert<
  88                 Pred, Insert, (bool)Pred::template apply<Insert, Right2>::value,
  89                 std::index_sequence<Left..., Right1>,
  90                 Right2, Right...
  91             >::type;
  92         };
  93
  94         // We did not find the insertion point, but there is only one element
  95         // left. We insert at the end of the list, and we're done.
  96         template <typename Pred, std::size_t Insert, std::size_t ...Left, std::size_t Last>
  97         struct insert<Pred, Insert, false, std::index_sequence<Left...>, Last> {
  98             using type = std::index_sequence<Left..., Last, Insert>;
  99         };
 100
 101         // We found the insertion point, we're done.
 102         template <typename Pred, std::size_t Insert, std::size_t ...Left, std::size_t ...Right>
 103         struct insert<Pred, Insert, true, std::index_sequence<Left...>, Right...> {
 104             using type = std::index_sequence<Left..., Insert, Right...>;
 105         };
 106
 107
 108         template <typename Pred, typename Result, std::size_t ...T>
 109         struct insertion_sort_impl;
 110
 111         template <typename Pred,
 112                   std::size_t Result1, std::size_t ...Result,
 113                   std::size_t T, std::size_t ...Ts>
 114         struct insertion_sort_impl<Pred, std::index_sequence<Result1, Result...>, T, Ts...> {
 115             using type = typename insertion_sort_impl<
 116                 Pred,
 117                 typename insert<
 118                     Pred, T, (bool)Pred::template apply<T, Result1>::value,
 119                     std::index_sequence<>,
 120                     Result1, Result...
 121                 >::type,
 122                 Ts...
 123             >::type;
 124         };
 125
 126         template <typename Pred, std::size_t T, std::size_t ...Ts>
 127         struct insertion_sort_impl<Pred, std::index_sequence<>, T, Ts...> {
 128             using type = typename insertion_sort_impl<
 129                 Pred, std::index_sequence<T>, Ts...
 130             >::type;
 131         };
 132
 133         template <typename Pred, typename Result>
 134         struct insertion_sort_impl<Pred, Result> {
 135             using type = Result;
 136         };
 137
 138         template <typename Pred, typename Indices>
 139         struct sort_helper;
 140
 141         template <typename Pred, std::size_t ...i>
 142         struct sort_helper<Pred, std::index_sequence<i...>> {
 143             using type = typename insertion_sort_impl<
 144                 Pred, std::index_sequence<>, i...
 145             >::type;
 146         };
 147     } // end namespace detail
 148
 149     template <typename S, bool condition>
 150     struct sort_impl<S, when<condition>> : default_ {
 151         template <typename Xs, std::size_t ...i>
 152         static constexpr auto apply_impl(Xs&& xs, std::index_sequence<i...>) {
 153             return hana::make<S>(hana::at_c<i>(static_cast<Xs&&>(xs))...);
 154         }
 155
 156         template <typename Xs, typename Pred>
 157         static constexpr auto apply(Xs&& xs, Pred const&) {
 158             constexpr std::size_t Len = decltype(hana::length(xs))::value;
 159             using Indices = typename detail::sort_helper<
 160                 detail::sort_predicate<Xs&&, Pred>,
 161                 std::make_index_sequence<Len>
 162             >::type;
 163
 164             return apply_impl(static_cast<Xs&&>(xs), Indices{});
 165         }
 166
 167         template <typename Xs>
 168         static constexpr auto apply(Xs&& xs)
 169         { return sort_impl::apply(static_cast<Xs&&>(xs), hana::less); }
 170     };
 171 BOOST_HANA_NAMESPACE_END
 172
 173 #endif // !BOOST_HANA_SORT_HPP