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

   1 /*=============================================================================
   2     Copyright (c) 2001-2006 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_IMPL_07172005_0952)
   8 #define FUSION_VALUE_AT_IMPL_07172005_0952
   9
  10 #include <boost/fusion/support/detail/access.hpp>
  11 #include <boost/type_traits/is_const.hpp>
  12 #include <boost/mpl/eval_if.hpp>
  13 #include <boost/mpl/bool.hpp>
  14
  15 namespace boost { namespace fusion
  16 {
  17     struct cons_tag;
  18
  19     namespace extension
  20     {
  21         template <typename Tag>
  22         struct value_at_impl;
  23
  24         template <>
  25         struct value_at_impl<cons_tag>
  26         {
  27             template <typename Sequence, typename N>
  28             struct apply
  29             {
  30                 typedef typename
  31                     mpl::eval_if<
  32                         mpl::bool_<N::value == 0>
  33                       , mpl::identity<typename Sequence::car_type>
  34                       , apply<typename Sequence::cdr_type, mpl::int_<N::value-1> >
  35                     >::type
  36                 type;
  37             };
  38         };
  39     }
  40 }}
  41
  42 #endif