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
15namespace 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
21template < 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.
30template < typename K, typename V >
31void 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.
37template < typename Key, typename Value >
38inline null_property_map< Key, Value > make_null_property()
39{
40 return null_property_map< Key, Value >();
41}
42}
43
44#endif
45