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 > struct null_property_map
  22 {
  23     typedef Key key_type;
  24     typedef Value value_type;
  25     typedef void reference;
  26     typedef boost::writable_property_map_tag category;
  27 };
  28
  29 // The null_property_map<K,V> only has a put() function.
  30 template < typename K, typename V >
  31 void put(
  32     null_property_map< K, V >& /*pm*/, const K& /*key*/, const V& /*value*/)
  33 {
  34 }
  35
  36 // A helper function for intantiating null property maps.
  37 template < typename Key, typename Value >
  38 inline null_property_map< Key, Value > make_null_property()
  39 {
  40     return null_property_map< Key, Value >();
  41 }
  42 }
  43
  44 #endif