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