boost/fusion/container/map/detail/at_key_impl.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2013 Joel de Guzman
   3
   4     Distributed under the Boost Software License, Version 1.0. (See accompanying
   5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 ==============================================================================*/
   7 #if !defined(BOOST_FUSION_MAP_DETAIL_AT_KEY_IMPL_02042013_0821)
   8 #define BOOST_FUSION_MAP_DETAIL_AT_KEY_IMPL_02042013_0821
   9
  10 #include <boost/fusion/support/config.hpp>
  11 #include <boost/fusion/support/detail/access.hpp>
  12 #include <boost/type_traits/is_const.hpp>
  13 #include <boost/mpl/at.hpp>
  14 #include <boost/mpl/identity.hpp>
  15
  16 namespace boost { namespace fusion
  17 {
  18     struct map_tag;
  19
  20     namespace extension
  21     {
  22         template <typename Tag>
  23         struct at_key_impl;
  24
  25         template <>
  26         struct at_key_impl<map_tag>
  27         {
  28             template <typename Sequence, typename Key>
  29             struct apply
  30             {
  31                 typedef
  32                     decltype(std::declval<Sequence>().get(mpl::identity<Key>()))
  33                 type;
  34
  35                 BOOST_FUSION_GPU_ENABLED
  36                 static type
  37                 call(Sequence& m)
  38                 {
  39                     return m.get(mpl::identity<Key>());
  40                 }
  41             };
  42
  43             template <typename Sequence, typename Key>
  44             struct apply<Sequence const, Key>
  45             {
  46                 typedef
  47                     decltype(std::declval<Sequence const>().get(mpl::identity<Key>()))
  48                 type;
  49
  50                 BOOST_FUSION_GPU_ENABLED
  51                 static type
  52                 call(Sequence const& m)
  53                 {
  54                     return m.get(mpl::identity<Key>());
  55                 }
  56             };
  57         };
  58     }
  59 }}
  60
  61 #endif