text: /*=============================================================================
      Copyright (c) 2001-2011 Joel de Guzman
  
      Distributed under the Boost Software License, Version 1.0. (See accompanying 
      file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  ==============================================================================*/
  #if !defined(FUSION_DISTANCE_09172005_0721)
  #define FUSION_DISTANCE_09172005_0721
  
  #include <boost/fusion/support/config.hpp>
  #include <boost/fusion/iterator/detail/distance.hpp>
  #include <boost/fusion/support/category_of.hpp>
  
  #include <boost/mpl/int.hpp>
  #include <boost/mpl/assert.hpp>
  #include <boost/type_traits/is_same.hpp>
  
  #include <boost/fusion/support/tag_of.hpp>
  
  namespace boost { namespace fusion
  {
      struct random_access_traversal_tag;
  
      // Special tags:
      struct iterator_facade_tag; // iterator facade tag
      struct boost_array_iterator_tag; // boost::array iterator tag
      struct mpl_iterator_tag; // mpl sequence iterator tag
      struct std_pair_iterator_tag; // std::pair iterator tag
  
      namespace extension
      {
          template <typename Tag>
          struct distance_impl
          {
              // default implementation
              template <typename First, typename Last>
              struct apply : distance_detail::linear_distance<First, Last> 
              {};
          };
  
          template <>
          struct distance_impl<iterator_facade_tag>
          {
              template <typename First, typename Last>
              struct apply : First::template distance<First, Last> {};
          };
  
          template <>
          struct distance_impl<boost_array_iterator_tag>;
  
          template <>
          struct distance_impl<mpl_iterator_tag>;
  
          template <>
          struct distance_impl<std_pair_iterator_tag>;
      }
  
      namespace result_of
      {
          template <typename First, typename Last>
          struct distance
            : extension::distance_impl<typename detail::tag_of<First>::type>::
                  template apply<First, Last>
          {
              typedef typename extension::distance_impl<typename detail::tag_of<First>::type>:: 
              template apply<First, Last>::type distance_application;
              BOOST_STATIC_CONSTANT(int, value = distance_application::value);
          };
      }
          
      template <typename First, typename Last>
      BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
      inline typename result_of::distance<First, Last>::type
      distance(First const& a, Last const& b)
      {
          return result_of::distance<First, Last>::call(a,b);
      }
  }}
  
  #endif
  