Hello, the program below does not compile at least with g++ 5.3.1 and clang++ 3.5.2-1 when using c++11 standard. If I comment line #1 it compiles. If I change #2 to undirectedS it compiles. Is there anything wrong in my code or is it a problem in boost's? Thanks, Sebastien. #include struct A { A(){} A(const A& ){} // #1 A& operator=(const A&){return *this;} }; typedef boost::adjacency_list Graph; int main() { Graph g; boost::add_vertex(g); return 0; }