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