to Boost Graph Library designers: in the boost/graph/graph_traits.hpp (line 104): //--begin---------------------------------------------------------------- // Since pair is in namespace std, Koenig lookup will find source and // target if they are also defined in namespace std. This is illegal, // but the alternative is to put source and target in the global // namespace which causes name conflicts with other libraries (like // SUIF). namespace std { template T source(pair p, const G&) { return p.first; } template T target(pair p, const G&) { return p.second; } } //--end---------------------------------------------------------------- why not change it with: //--begin---------------------------------------------------------------- template typename boost::graph_traits<G>::vertex_descriptor source(E e, const G& g) { return boost::source(e,g); } template typename boost::graph_traits<G>::vertex_descriptor target(E e, const G& g) { return boost::target(e,g); } //--end---------------------------------------------------------------- and add the following in boost/graph/vector_as_graph.hpp //--begin---------------------------------------------------------------- template T source(std::pair p, const std::vector&) { return p.first; } template T target(std::pair p, const std::vector&) { return p.second; } //---end--------------------------------------------------------------- which means, vector_as_graph handles source() and target() inside its class (and in boost namespace) and makes std::source() and std::target() more general the reason why I want to modify this is that the original design makes trouble when I try to develop a subgraph view adaptor (something like filtered_graph, but accept vector_as_graph type) I need to define my own source() and target() to deal with my own subgraph view class, as shown below: namespace boost { template <class G> typename subview_graph<G>::vertex_descriptor target(typename subview_graph<G>::edge_descriptor e, subview_graph<G>& v) {...} } however, when dealing with vector_as_graph (which means the 1st argument, edge_descriptor, will be std::pair), the compiler complains ambiguity between std::target() and boost::target() in fact, it will make trouble to everyone who wants to define his/her own source() & target() function but the 1st argument is std::pair if it's possible, please fix this strange design or any other opinions will be appreciated best regards, hcyeh