ceph/src/boost/libs/fusion/include/boost/fusion/sequence/intrinsic/value_at_key.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2011 Joel de Guzman
   3     Copyright (c) 2006 Dan Marsden
   4
   5     Distributed under the Boost Software License, Version 1.0. (See accompanying
   6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7 ==============================================================================*/
   8 #if !defined(FUSION_VALUE_AT_KEY_05052005_0229)
   9 #define FUSION_VALUE_AT_KEY_05052005_0229
  10
  11 #include <boost/fusion/support/config.hpp>
  12 #include <boost/mpl/int.hpp>
  13 #include <boost/mpl/empty_base.hpp>
  14 #include <boost/mpl/if.hpp>
  15 #include <boost/mpl/or.hpp>
  16 #include <boost/fusion/sequence/intrinsic_fwd.hpp>
  17 #include <boost/fusion/sequence/intrinsic/has_key.hpp>
  18 #include <boost/fusion/iterator/value_of_data.hpp>
  19 #include <boost/fusion/algorithm/query/find.hpp>
  20 #include <boost/fusion/support/tag_of.hpp>
  21 #include <boost/fusion/support/category_of.hpp>
  22
  23 namespace boost { namespace fusion
  24 {
  25     // Special tags:
  26     struct sequence_facade_tag;
  27     struct boost_array_tag; // boost::array tag
  28     struct mpl_sequence_tag; // mpl sequence tag
  29     struct std_pair_tag; // std::pair tag
  30
  31     namespace extension
  32     {
  33         template <typename Tag>
  34         struct value_at_key_impl
  35         {
  36             template <typename Seq, typename Key>
  37             struct apply
  38               : result_of::value_of_data<
  39                     typename result_of::find<Seq, Key>::type
  40                 >
  41             {};
  42         };
  43
  44         template <>
  45         struct value_at_key_impl<sequence_facade_tag>
  46         {
  47             template <typename Sequence, typename Key>
  48             struct apply : Sequence::template value_at_key<Sequence, Key> {};
  49         };
  50
  51         template <>
  52         struct value_at_key_impl<boost_array_tag>;
  53
  54         template <>
  55         struct value_at_key_impl<mpl_sequence_tag>;
  56
  57         template <>
  58         struct value_at_key_impl<std_pair_tag>;
  59     }
  60
  61     namespace detail
  62     {
  63         template <typename Sequence, typename N, typename Tag>
  64         struct value_at_key_impl
  65             : mpl::if_<
  66                   mpl::or_<
  67                       typename extension::has_key_impl<Tag>::template apply<Sequence, N>
  68                     , traits::is_unbounded<Sequence>
  69                   >
  70                 , typename extension::value_at_key_impl<Tag>::template apply<Sequence, N>
  71                 , mpl::empty_base
  72               >::type
  73         {};
  74     }
  75
  76     namespace result_of
  77     {
  78         template <typename Sequence, typename N>
  79         struct value_at_key
  80             : detail::value_at_key_impl<Sequence, N, typename detail::tag_of<Sequence>::type>
  81         {};
  82     }
  83 }}
  84
  85 #endif
  86