Hello all, Quoting from page 24 of "The Boost Graph Library; User Guide and Reference Manual": "It turns out that by the contravariance subtyping rule, the parameter type in the derived classes member function must be either the same type or a base class of the type as the parameter in the base class." Now please consider this code: #include <iostream> struct base_1 {}; struct derived_1: base_1 {}; struct base_2 { virtual void foo(derived_1 *p) {std::cout << "base_2::foo()\n";} }; struct derived_2: base_2 { virtual void foo(base_1 *p) {std::cout << "derived_2::foo()\n";} }; int main() { base_2 *ptr = new derived_2; ptr->foo(new derived_1); } This outputs base_2::foo(). Why? The quoted passage implies derived_2::foo() should override base_2::foo(). Clearly, it does not. Furthermore, I cannot find anything in the Standard that indicates it should. So, I am clearly misinterpreting the quoted passage. Can anybody explain to me what was meant in that passage? Thank you, Dave