boost/fusion/container/deque/detail/value_at_impl.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2006 Joel de Guzman
   3     Copyright (c) 2005-2006 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(BOOST_FUSION_DEQUE_VALUE_AT_IMPL_08122006_0756)
   9 #define BOOST_FUSION_DEQUE_VALUE_AT_IMPL_08122006_0756
  10
  11 #include <boost/fusion/container/deque/detail/keyed_element.hpp>
  12
  13 #include <boost/mpl/equal_to.hpp>
  14 #include <boost/mpl/assert.hpp>
  15
  16 namespace boost { namespace fusion {
  17
  18     struct deque_tag;
  19
  20     namespace extension
  21     {
  22         template<typename T>
  23         struct value_at_impl;
  24
  25         template<>
  26         struct value_at_impl<deque_tag>
  27         {
  28             template<typename Sequence, typename N>
  29             struct apply
  30             {
  31                 typedef typename Sequence::next_up next_up;
  32                 typedef typename Sequence::next_down next_down;
  33                 BOOST_MPL_ASSERT_RELATION(next_down::value, !=, next_up::value);
  34
  35                 typedef mpl::plus<next_down, mpl::int_<1> > offset;
  36                 typedef mpl::int_<mpl::plus<N, offset>::value> adjusted_index;
  37                 typedef typename detail::keyed_element_value_at<Sequence, adjusted_index>::type type;
  38             };
  39         };
  40     }
  41 }}
  42
  43 #endif