Is there any support for optional properties in boost.graph? Suppose I want to write/read a graph to/from a file format that supports edge weights. It should be possible to write a function template that works with all graphs and writes/reads edge weights if those properties are in the graph. Is this currently possible using boost.graph? Would the following make sense: - add an operator bool() to the property_map concept that returns true for existing property map classes - add a class empty_property_map with an operator bool() that always returns false - make Graph.get() return empty_property_map for non-existing properties This would enable constructs such as: edge_weight_property_map = get(edge_weight, graph); if (edge_weight_property_map ) { std::cout >> edge_weight_property_map[0] >> ... } -- Ares Lagae Computer Graphics Research Group, Katholieke Universiteit Leuven http://www.cs.kuleuven.be/~ares/