1 /*============================================================================= 2 Copyright (c) 2001-2011 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(FUSION_VALUE_AT_05052005_0229) 8 #define FUSION_VALUE_AT_05052005_0229 9 10 #include <boost/fusion/support/config.hpp> 11 #include <boost/mpl/int.hpp> 12 #include <boost/mpl/if.hpp> 13 #include <boost/mpl/or.hpp> 14 #include <boost/mpl/less.hpp> 15 #include <boost/mpl/empty_base.hpp> 16 #include <boost/fusion/sequence/intrinsic_fwd.hpp> 17 #include <boost/fusion/support/tag_of.hpp> 18 #include <boost/fusion/support/category_of.hpp> 19 20 namespace boost { namespace fusion 21 { 22 // Special tags: 23 struct sequence_facade_tag; 24 struct boost_tuple_tag; // boost::tuples::tuple tag 25 struct boost_array_tag; // boost::array tag 26 struct mpl_sequence_tag; // mpl sequence tag 27 struct std_pair_tag; // std::pair tag 28 29 namespace extension 30 { 31 template <typename Tag> 32 struct value_at_impl 33 { 34 template <typename Sequence, typename N> 35 struct apply; 36 }; 37 38 template <> 39 struct value_at_impl<sequence_facade_tag> 40 { 41 template <typename Sequence, typename N> 42 struct apply : Sequence::template value_at<Sequence, N> {}; 43 }; 44 45 template <> 46 struct value_at_impl<boost_tuple_tag>; 47 48 template <> 49 struct value_at_impl<boost_array_tag>; 50 51 template <> 52 struct value_at_impl<mpl_sequence_tag>; 53 54 template <> 55 struct value_at_impl<std_pair_tag>; 56 } 57 58 namespace detail 59 { 60 template <typename Sequence, typename N, typename Tag> 61 struct value_at_impl 62 : mpl::if_< 63 mpl::or_< 64 mpl::less<N, typename extension::size_impl<Tag>::template apply<Sequence>::type> 65 , traits::is_unbounded<Sequence> 66 > 67 , typename extension::value_at_impl<Tag>::template apply<Sequence, N> 68 , mpl::empty_base 69 >::type 70 {}; 71 } 72 73 namespace result_of 74 { 75 template <typename Sequence, typename N> 76 struct value_at 77 : detail::value_at_impl<Sequence, N, typename detail::tag_of<Sequence>::type> 78 {}; 79 80 template <typename Sequence, int N> 81 struct value_at_c 82 : fusion::result_of::value_at<Sequence, mpl::int_<N> > 83 {}; 84 } 85 }} 86 87 #endif 88 89