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

   1 /*!
   2 @file
   3 Defines `boost::hana::at_key`.
   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_AT_KEY_HPP
  11 #define BOOST_HANA_AT_KEY_HPP
  12
  13 #include <boost/hana/fwd/at_key.hpp>
  14
  15 #include <boost/hana/accessors.hpp>
  16 #include <boost/hana/at.hpp>
  17 #include <boost/hana/concept/searchable.hpp>
  18 #include <boost/hana/concept/struct.hpp>
  19 #include <boost/hana/config.hpp>
  20 #include <boost/hana/core/dispatch.hpp>
  21 #include <boost/hana/detail/decay.hpp>
  22 #include <boost/hana/equal.hpp>
  23 #include <boost/hana/find.hpp>
  24 #include <boost/hana/find_if.hpp>
  25 #include <boost/hana/first.hpp>
  26 #include <boost/hana/functional/on.hpp>
  27 #include <boost/hana/length.hpp>
  28 #include <boost/hana/optional.hpp>
  29 #include <boost/hana/second.hpp>
  30
  31 #include <cstddef>
  32 #include <utility>
  33
  34
  35 BOOST_HANA_NAMESPACE_BEGIN
  36     //! @cond
  37     template <typename Xs, typename Key>
  38     constexpr decltype(auto) at_key_t::operator()(Xs&& xs, Key const& key) const {
  39         using S = typename hana::tag_of<Xs>::type;
  40         using AtKey = BOOST_HANA_DISPATCH_IF(at_key_impl<S>,
  41             hana::Searchable<S>::value
  42         );
  43
  44     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  45         static_assert(hana::Searchable<S>::value,
  46         "hana::at_key(xs, key) requires 'xs' to be Searchable");
  47     #endif
  48
  49         return AtKey::apply(static_cast<Xs&&>(xs), key);
  50     }
  51     //! @endcond
  52
  53     template <typename S, bool condition>
  54     struct at_key_impl<S, when<condition>> : default_ {
  55         template <typename Xs, typename Key>
  56         static constexpr auto apply(Xs&& xs, Key const& key) {
  57             return hana::find(static_cast<Xs&&>(xs), key).value();
  58         }
  59     };
  60
  61     namespace at_key_detail {
  62         template <typename T>
  63         struct equal_to {
  64             T const& t;
  65             template <typename U>
  66             constexpr auto operator()(U const& u) const {
  67                 return hana::equal(t, u);
  68             }
  69         };
  70
  71         //! @todo This causes an awful duplication of code with `find_if`.
  72         template <typename Xs, typename Pred, std::size_t i, std::size_t N, bool Done>
  73         struct advance_until;
  74
  75         template <typename Xs, typename Pred, std::size_t i, std::size_t N>
  76         struct advance_until<Xs, Pred, i, N, false>
  77             : advance_until<Xs, Pred, i + 1, N, static_cast<bool>(detail::decay<decltype(
  78                 std::declval<Pred>()(hana::at_c<i>(std::declval<Xs>()))
  79             )>::type::value)>
  80         { };
  81
  82         template <typename Xs, typename Pred, std::size_t N>
  83         struct advance_until<Xs, Pred, N, N, false> {
  84             template <typename Ys>
  85             static constexpr auto apply(Ys&&) = delete;
  86         };
  87
  88         template <typename Xs, typename Pred, std::size_t i, std::size_t N>
  89         struct advance_until<Xs, Pred, i, N, true> {
  90             template <typename Ys>
  91             static constexpr decltype(auto) apply(Ys&& ys) {
  92                 return hana::at_c<i - 1>(static_cast<Ys&&>(ys));
  93             }
  94         };
  95     }
  96
  97     template <typename S>
  98     struct at_key_impl<S, when<hana::Sequence<S>::value>> {
  99         template <typename Xs, typename Key>
 100         static constexpr decltype(auto) apply(Xs&& xs, Key const&) {
 101             constexpr std::size_t N = decltype(hana::length(xs))::value;
 102             using Pred = at_key_detail::equal_to<Key>;
 103             return at_key_detail::advance_until<Xs&&, Pred, 0, N, false>::apply(
 104                 static_cast<Xs&&>(xs)
 105             );
 106         }
 107     };
 108
 109     template <typename S>
 110     struct at_key_impl<S, when<hana::Struct<S>::value>> {
 111         template <typename X, typename Key>
 112         static constexpr decltype(auto) apply(X&& x, Key const& key) {
 113             auto accessor = hana::second(*hana::find_if(hana::accessors<S>(),
 114                 hana::equal.to(key) ^hana::on^ hana::first
 115             ));
 116             return accessor(static_cast<X&&>(x));
 117         }
 118     };
 119 BOOST_HANA_NAMESPACE_END
 120
 121 #endif // !BOOST_HANA_AT_KEY_HPP