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

   1 /*!
   2 @file
   3 Defines `boost::hana::lexicographical_compare`.
   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_LEXICOGRAPHICAL_COMPARE_HPP
  11 #define BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP
  12
  13 #include <boost/hana/fwd/lexicographical_compare.hpp>
  14
  15 #include <boost/hana/bool.hpp>
  16 #include <boost/hana/concept/iterable.hpp>
  17 #include <boost/hana/config.hpp>
  18 #include <boost/hana/core/dispatch.hpp>
  19 #include <boost/hana/drop_front.hpp>
  20 #include <boost/hana/front.hpp>
  21 #include <boost/hana/if.hpp>
  22 #include <boost/hana/is_empty.hpp>
  23 #include <boost/hana/less.hpp>
  24
  25
  26 BOOST_HANA_NAMESPACE_BEGIN
  27     //! @cond
  28     template <typename Xs, typename Ys>
  29     constexpr auto lexicographical_compare_t::operator()(Xs const& xs, Ys const& ys) const {
  30         return hana::lexicographical_compare(xs, ys, hana::less);
  31     }
  32
  33     template <typename Xs, typename Ys, typename Pred>
  34     constexpr auto lexicographical_compare_t::operator()(Xs const& xs, Ys const& ys, Pred const& pred) const {
  35         using It1 = typename hana::tag_of<Xs>::type;
  36         using It2 = typename hana::tag_of<Ys>::type;
  37         using LexicographicalCompare = BOOST_HANA_DISPATCH_IF(
  38             lexicographical_compare_impl<It1>,
  39             hana::Iterable<It1>::value &&
  40             hana::Iterable<It2>::value
  41         );
  42
  43     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  44         static_assert(hana::Iterable<It1>::value,
  45         "hana::lexicographical_compare(xs, ys, pred) requires 'xs' to be Iterable");
  46
  47         static_assert(hana::Iterable<It2>::value,
  48         "hana::lexicographical_compare(xs, ys, pred) requires 'ys' to be Iterable");
  49     #endif
  50
  51         return LexicographicalCompare::apply(xs, ys, pred);
  52     }
  53     //! @endcond
  54
  55     template <typename It, bool condition>
  56     struct lexicographical_compare_impl<It, when<condition>> : default_ {
  57         template <typename Xs, typename Ys, typename Pred>
  58         static constexpr auto
  59         helper2(Xs const&, Ys const&, Pred const&, hana::true_)
  60         { return hana::false_c; }
  61
  62         template <typename Xs, typename Ys, typename Pred>
  63         static constexpr auto
  64         helper2(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_)
  65         { return apply(hana::drop_front(xs), hana::drop_front(ys), pred); }
  66
  67         template <typename Xs, typename Ys, typename Pred>
  68         static constexpr auto
  69         helper2(Xs const& xs, Ys const& ys, Pred const& pred, bool is_greater)
  70         { return is_greater ? false : apply(hana::drop_front(xs), hana::drop_front(ys), pred); }
  71
  72
  73         template <typename Xs, typename Ys, typename Pred>
  74         static constexpr auto
  75         helper1(Xs const&, Ys const&, Pred const&, hana::true_)
  76         { return hana::true_c; }
  77
  78         template <typename Xs, typename Ys, typename Pred>
  79         static constexpr auto
  80         helper1(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_)
  81         { return helper2(xs, ys, pred, hana::if_(pred(hana::front(ys), hana::front(xs)), hana::true_c, hana::false_c)); }
  82
  83         template <typename Xs, typename Ys, typename Pred>
  84         static constexpr auto
  85         helper1(Xs const& xs, Ys const& ys, Pred const& pred, bool is_less)
  86         { return is_less ? true : helper2(xs, ys, pred, hana::if_(pred(hana::front(ys), hana::front(xs)), hana::true_c, hana::false_c)); }
  87
  88
  89         template <typename Xs, typename Ys, typename Pred>
  90         static constexpr auto
  91         helper(Xs const&, Ys const& ys, Pred const&, hana::true_)
  92         { return hana::not_(hana::is_empty(ys)); }
  93
  94         template <typename Xs, typename Ys, typename Pred>
  95         static constexpr auto
  96         helper(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_)
  97         { return helper1(xs, ys, pred, hana::if_(pred(hana::front(xs), hana::front(ys)), hana::true_c, hana::false_c)); }
  98
  99
 100         template <typename Xs, typename Ys, typename Pred>
 101         static constexpr auto apply(Xs const& xs, Ys const& ys, Pred const& pred) {
 102             return helper(xs, ys, pred, hana::bool_c<
 103                 decltype(hana::is_empty(xs))::value ||
 104                 decltype(hana::is_empty(ys))::value
 105             >);
 106         }
 107     };
 108 BOOST_HANA_NAMESPACE_END
 109
 110 #endif // !BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP