[Boost-users] astar using namespace

I've removed the using namespace boost from the astar graph cities example. (I prefer to define namespaces explicitly). //using namespace boost; I've added boost:: to all the type names and it all compiles fine. However, some functions compile without the namespace. ie the following line: WeightMap weightmap = get(boost::edge_weight, g); Can someone please explain why I dont need a boost:: infront of the get?