Chris@16: // (C) Copyright Andrew Sutton 2007
Chris@16: //
Chris@16: // Use, modification and distribution are subject to the
Chris@16: // Boost Software License, Version 1.0 (See accompanying file
Chris@16: // LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef BOOST_GRAPH_NULL_PROPERTY_HPP
Chris@16: #define BOOST_GRAPH_NULL_PROPERTY_HPP
Chris@16: 
Chris@16: #include <boost/property_map/property_map.hpp>
Chris@16: 
Chris@16: // TODO: This should really be part of the property maps library rather than
Chris@16: // the Boost.Graph library.
Chris@16: 
Chris@16: namespace boost
Chris@16: {
Chris@16:     // A null property is somewhat like the inverse of the constant
Chris@16:     // property map except that instead of returning a single value,
Chris@16:     // this eats any writes and cannot be read from.
Chris@16: 
Chris@16:     template <typename Key, typename Value>
Chris@16:     struct null_property_map
Chris@16:     {
Chris@16:         typedef Key key_type;
Chris@16:         typedef Value value_type;
Chris@16:         typedef void reference;
Chris@16:         typedef boost::writable_property_map_tag category;
Chris@16:     };
Chris@16: 
Chris@16:     // The null_property_map<K,V> only has a put() function.
Chris@16:     template <typename K, typename V>
Chris@16:     void put(null_property_map<K,V>& /*pm*/, const K& /*key*/, const V& /*value*/)
Chris@16:     { }
Chris@16: 
Chris@16:     // A helper function for intantiating null property maps.
Chris@16:     template <typename Key, typename Value>
Chris@16:     inline null_property_map<Key, Value> make_null_property()
Chris@16:     { return null_property_map<Key, Value>(); }
Chris@16: }
Chris@16: 
Chris@16: #endif