single_view/detail/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_AT_IMPL_JUL_07_2011_1348PM)
0009 #define BOOST_FUSION_SINGLE_VIEW_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
0016 namespace boost { namespace fusion
0017 {
0018     struct single_view_tag;
0019
0020     namespace extension
0021     {
0022         template<typename Tag>
0023         struct at_impl;
0024
0025         template<>
0026         struct at_impl<single_view_tag>
0027         {
0028             template<typename Sequence, typename N>
0029             struct apply
0030             {
0031                 BOOST_MPL_ASSERT((mpl::equal_to<N, mpl::int_<0> >));
0032                 typedef typename Sequence::value_type type;
0033
0034                 BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
0035                 static type
0036                 call(Sequence& seq)
0037                 {
0038                     return seq.val;
0039                 }
0040             };
0041         };
0042     }
0043
0044 }}
0045
0046 #endif