ceph/src/boost/boost/hana/equal.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::equal`.
   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_EQUAL_HPP
  11 #define BOOST_HANA_EQUAL_HPP
  12
  13 #include <boost/hana/fwd/equal.hpp>
  14
  15 #include <boost/hana/accessors.hpp>
  16 #include <boost/hana/all_of.hpp>
  17 #include <boost/hana/and.hpp>
  18 #include <boost/hana/at.hpp>
  19 #include <boost/hana/bool.hpp>
  20 #include <boost/hana/concept/comparable.hpp>
  21 #include <boost/hana/concept/constant.hpp>
  22 #include <boost/hana/concept/product.hpp>
  23 #include <boost/hana/concept/sequence.hpp>
  24 #include <boost/hana/concept/struct.hpp>
  25 #include <boost/hana/config.hpp>
  26 #include <boost/hana/core/common.hpp>
  27 #include <boost/hana/core/to.hpp>
  28 #include <boost/hana/core/dispatch.hpp>
  29 #include <boost/hana/core/tag_of.hpp>
  30 #include <boost/hana/core/when.hpp>
  31 #include <boost/hana/detail/concepts.hpp>
  32 #include <boost/hana/detail/has_common_embedding.hpp>
  33 #include <boost/hana/detail/nested_to.hpp> // required by fwd decl
  34 #include <boost/hana/first.hpp>
  35 #include <boost/hana/if.hpp>
  36 #include <boost/hana/length.hpp>
  37 #include <boost/hana/second.hpp>
  38 #include <boost/hana/value.hpp>
  39
  40 #include <cstddef>
  41
  42
  43 BOOST_HANA_NAMESPACE_BEGIN
  44     //! @cond
  45     template <typename X, typename Y>
  46     constexpr auto equal_t::operator()(X&& x, Y&& y) const {
  47         using T = typename hana::tag_of<X>::type;
  48         using U = typename hana::tag_of<Y>::type;
  49         using Equal = equal_impl<T, U>;
  50         return Equal::apply(static_cast<X&&>(x), static_cast<Y&&>(y));
  51     }
  52     //! @endcond
  53
  54     template <typename T, typename U, bool condition>
  55     struct equal_impl<T, U, when<condition>> : default_ {
  56         template <typename X, typename Y>
  57         static constexpr auto apply(X const&, Y const&) {
  58             // Delay the static_assert by ensuring T_ is dependent.
  59             using T_ = typename hana::tag_of<X>::type;
  60             static_assert(!hana::is_convertible<T_, U>::value &&
  61                           !hana::is_convertible<U, T_>::value,
  62             "No default implementation of hana::equal is provided for related "
  63             "types that can't be safely embedded into a common type, because "
  64             "those are most likely programming errors. If this is really what "
  65             "you want, you can manually convert both objects to a common "
  66             "Comparable type before performing the comparison. If you think "
  67             "you have made your types Comparable but you see this, perhaps you "
  68             "forgot to define some of the necessary methods for an automatic "
  69             "model of Comparable to kick in. A possible culprit is defining "
  70             "'operator==' but not 'operator!='.");
  71
  72             return hana::false_c;
  73         }
  74     };
  75
  76     // Cross-type overload
  77     template <typename T, typename U>
  78     struct equal_impl<T, U, when<
  79         detail::has_nontrivial_common_embedding<Comparable, T, U>::value &&
  80         !detail::EqualityComparable<T, U>::value
  81     >> {
  82         using C = typename hana::common<T, U>::type;
  83         template <typename X, typename Y>
  84         static constexpr auto apply(X&& x, Y&& y) {
  85             return hana::equal(hana::to<C>(static_cast<X&&>(x)),
  86                                hana::to<C>(static_cast<Y&&>(y)));
  87         }
  88     };
  89
  90     //////////////////////////////////////////////////////////////////////////
  91     // Model for EqualityComparable data types
  92     //////////////////////////////////////////////////////////////////////////
  93     template <typename T, typename U>
  94     struct equal_impl<T, U, when<detail::EqualityComparable<T, U>::value>> {
  95         template <typename X, typename Y>
  96         static constexpr auto apply(X&& x, Y&& y)
  97         { return static_cast<X&&>(x) == static_cast<Y&&>(y); }
  98     };
  99
 100     //////////////////////////////////////////////////////////////////////////
 101     // Model for Constants wrapping a Comparable
 102     //////////////////////////////////////////////////////////////////////////
 103     template <typename C>
 104     struct equal_impl<C, C, when<
 105         hana::Constant<C>::value &&
 106         Comparable<typename C::value_type>::value
 107     >> {
 108         template <typename X, typename Y>
 109         static constexpr auto apply(X const&, Y const&) {
 110             constexpr auto eq = hana::equal(hana::value<X>(), hana::value<Y>());
 111             constexpr bool truth_value = hana::if_(eq, true, false);
 112             return hana::bool_<truth_value>{};
 113         }
 114     };
 115
 116     //////////////////////////////////////////////////////////////////////////
 117     // Comparable for Products
 118     //////////////////////////////////////////////////////////////////////////
 119     template <typename T, typename U>
 120     struct equal_impl<T, U, when<hana::Product<T>::value && hana::Product<U>::value>> {
 121         template <typename X, typename Y>
 122         static constexpr auto apply(X const& x, Y const& y) {
 123             return hana::and_(
 124                 hana::equal(hana::first(x), hana::first(y)),
 125                 hana::equal(hana::second(x), hana::second(y))
 126             );
 127         }
 128     };
 129
 130     //////////////////////////////////////////////////////////////////////////
 131     // Comparable for Sequences
 132     //////////////////////////////////////////////////////////////////////////
 133     namespace detail {
 134         template <typename Xs, typename Ys, std::size_t Length>
 135         struct compare_finite_sequences {
 136             Xs const& xs;
 137             Ys const& ys;
 138
 139             template <std::size_t i>
 140             constexpr auto apply(hana::false_, hana::true_) const {
 141                 return compare_finite_sequences::apply<i+1>(
 142                     hana::bool_<i+1 == Length>{},
 143                     hana::if_(hana::equal(hana::at_c<i>(xs), hana::at_c<i>(ys)),
 144                               hana::true_c, hana::false_c)
 145                 );
 146             }
 147
 148             template <std::size_t i>
 149             constexpr auto apply(hana::false_, hana::false_) const
 150             { return hana::false_c; }
 151
 152             template <std::size_t i, typename Result>
 153             constexpr auto apply(hana::true_, Result r) const
 154             { return r; }
 155
 156             template <std::size_t i>
 157             constexpr bool apply(hana::false_, bool b) const {
 158                 return b && compare_finite_sequences::apply<i+1>(
 159                     hana::bool_<i+1 == Length>{},
 160                     hana::if_(hana::equal(hana::at_c<i>(xs), hana::at_c<i>(ys)),
 161                               hana::true_c, hana::false_c)
 162                 );
 163             }
 164         };
 165     }
 166
 167     template <typename T, typename U>
 168     struct equal_impl<T, U, when<Sequence<T>::value && hana::Sequence<U>::value>> {
 169         template <typename Xs, typename Ys>
 170         static constexpr auto apply(Xs const& xs, Ys const& ys) {
 171             constexpr std::size_t xs_size = decltype(hana::length(xs))::value;
 172             constexpr std::size_t ys_size = decltype(hana::length(ys))::value;
 173             detail::compare_finite_sequences<Xs, Ys, xs_size> comp{xs, ys};
 174             return comp.template apply<0>(hana::bool_<xs_size == 0>{},
 175                                           hana::bool_<xs_size == ys_size>{});
 176         }
 177     };
 178
 179     namespace detail {
 180         template <typename X, typename Y>
 181         struct compare_struct_members {
 182             X const& x;
 183             Y const& y;
 184
 185             template <typename Member>
 186             constexpr auto operator()(Member&& member) const {
 187                 auto accessor = hana::second(static_cast<Member&&>(member));
 188                 return hana::equal(accessor(x), accessor(y));
 189             }
 190         };
 191     }
 192
 193     template <typename S>
 194     struct equal_impl<S, S, when<hana::Struct<S>::value>> {
 195         template <typename X, typename Y>
 196         static constexpr auto apply(X const& x, Y const& y) {
 197             return hana::all_of(hana::accessors<S>(),
 198                 detail::compare_struct_members<X, Y>{x, y});
 199         }
 200     };
 201 BOOST_HANA_NAMESPACE_END
 202
 203 #endif // !BOOST_HANA_EQUAL_HPP