ceph/src/boost/boost/graph/property_maps/null_property_map.hpp

   1 // (C) Copyright Andrew Sutton 2007
   2 //
   3 // Use, modification and distribution are subject to the
   4 // Boost Software License, Version 1.0 (See accompanying file
   5 // LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
   6
   7 #ifndef BOOST_GRAPH_NULL_PROPERTY_HPP
   8 #define BOOST_GRAPH_NULL_PROPERTY_HPP
   9
  10 #include <boost/property_map/property_map.hpp>
  11
  12 // TODO: This should really be part of the property maps library rather than
  13 // the Boost.Graph library.
  14
  15 namespace boost
  16 {
  17     // A null property is somewhat like the inverse of the constant
  18     // property map except that instead of returning a single value,
  19     // this eats any writes and cannot be read from.
  20
  21     template <typename Key, typename Value>
  22     struct null_property_map
  23     {
  24         typedef Key key_type;
  25         typedef Value value_type;
  26         typedef void reference;
  27         typedef boost::writable_property_map_tag category;
  28     };
  29
  30     // The null_property_map<K,V> only has a put() function.
  31     template <typename K, typename V>
  32     void put(null_property_map<K,V>& /*pm*/, const K& /*key*/, const V& /*value*/)
  33     { }
  34
  35     // A helper function for intantiating null property maps.
  36     template <typename Key, typename Value>
  37     inline null_property_map<Key, Value> make_null_property()
  38     { return null_property_map<Key, Value>(); }
  39 }
  40
  41 #endif