single_view/detail/value_at_impl.hpp

0001 /*=============================================================================
0002     Copyright (c) 2011 Eric Niebler
0003
0004     Distributed under the Boost Software License, Version 1.0. (See accompanying
0005     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 ==============================================================================*/
0007
0008 #if !defined(BOOST_FUSION_SINGLE_VIEW_VALUE_AT_IMPL_JUL_07_2011_1348PM)
0009 #define BOOST_FUSION_SINGLE_VIEW_VALUE_AT_IMPL_JUL_07_2011_1348PM
0010
0011 #include <boost/fusion/support/config.hpp>
0012 #include <boost/mpl/int.hpp>
0013 #include <boost/mpl/assert.hpp>
0014 #include <boost/mpl/equal_to.hpp>
0015 #include <boost/fusion/sequence/intrinsic/value_at.hpp>
0016
0017 namespace boost { namespace fusion
0018 {
0019     struct single_view_tag;
0020
0021     namespace extension
0022     {
0023         template<typename Tag>
0024         struct value_at_impl;
0025
0026         template<>
0027         struct value_at_impl<single_view_tag>
0028         {
0029             template<typename Sequence, typename N>
0030             struct apply
0031             {
0032                 BOOST_MPL_ASSERT((mpl::equal_to<N, mpl::int_<0> >));
0033                 typedef typename Sequence::value_type type;
0034             };
0035         };
0036     }
0037
0038 }}
0039
0040 #endif