text: // Boost.Bimap
  //
  // Copyright (c) 2006-2007 Matias Capeletto
  //
  // 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)
  
  /// \file relation/support/data_extractor.hpp
  /// \brief Data extraction functor.
  
  #ifndef BOOST_BIMAP_RELATION_SUPPORT_DATA_EXTRACTOR_HPP
  #define BOOST_BIMAP_RELATION_SUPPORT_DATA_EXTRACTOR_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER>=1200)
  #pragma once
  #endif
  
  #include <boost/config.hpp>
  
  #include <boost/bimap/relation/detail/metadata_access_builder.hpp>
  #include <functional>
  
  /** \struct boost::bimaps::relation::support::data_extractor
  
  \brief Data extraction functor.
  
  \ingroup relation_group
                                                                      **/
  
  #ifndef BOOST_BIMAP_DOXYGEN_WILL_NOT_PROCESS_THE_FOLLOWING_LINES
  
  namespace boost {
  namespace bimaps {
  namespace relation {
  namespace support {
  
  template< class Tag, class Relation >
  struct data_extractor_implementation;
  
  template< class Relation >
  struct data_extractor_implementation< member_at::left, Relation > :
      public std::unary_function<Relation,BOOST_DEDUCED_TYPENAME Relation::left_value_type>
  {
      BOOST_DEDUCED_TYPENAME Relation::left_value_type const &
          operator()(Relation const & rel) const
      {
          return rel.left;
      }
  
      BOOST_DEDUCED_TYPENAME Relation::left_value_type &
          operator()(Relation       & rel) const
      {
          return rel.left;
      }
  };
  
  template< class Relation >
  struct data_extractor_implementation< member_at::right, Relation > :
      public std::unary_function<Relation,BOOST_DEDUCED_TYPENAME Relation::right_value_type>
  {
      BOOST_DEDUCED_TYPENAME Relation::right_value_type const & 
          operator()(Relation const & rel) const
      {
          return rel.right;
      }
  
      BOOST_DEDUCED_TYPENAME Relation::right_value_type & 
          operator()(Relation       & rel) const
      {
          return rel.right;
      }
  };
  
  template< class Tag, class Relation >
  struct data_extractor
  {
      typedef data_extractor_implementation
      <
          BOOST_DEDUCED_TYPENAME member_with_tag<Tag,Relation>::type,
          Relation
  
      > type;
  };
  
  template< class Relation >
  struct both_keys_extractor
  {
      typedef BOOST_DEDUCED_TYPENAME Relation::storage_base result_type;
  
       const result_type & operator()(const Relation & rel) const
      {
          return rel;
      }
  
      result_type & operator()( Relation & rel) const
      {
          return rel;
      }
  };
  
  } // namespace support
  } // namespace relation
  } // namespace bimaps
  } // namespace boost
  
  #endif // BOOST_BIMAP_DOXYGEN_WILL_NOT_PROCESS_THE_FOLLOWING_LINES
  
  #endif // BOOST_BIMAP_RELATION_SUPPORT_DATA_EXTRACTOR_HPP
  
  