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 87