implicit_cast was once in cast.hpp, but as the comments says, it has been removed due to uncertain purpose. I have to purposes of which I am wondering how to do them otherwise: 1. take the address of the conversion 2. initialise a std::vector< int > with a boost::assign::list_of in a constructor initialiser The latter is a bit subtle. list_of uses a templated conversion operator to containers (but technically everything) and std::vector's ctor are then all tried with taking converted arguments, which leads into an ambiguity. Using implicit_cast solves the problem, since then the constructor call to std::vector and the call to the conversion operator in list_of are both taken as user defined conversions, and there can only be one of them. vector< int > v = list_of(1)(2); // works vector< int > v(list_of(1)(2)); // ambiguous ctor() : v(implicit_cast< vector< int > >(list_of(1)(2))) { } // ambiguous ctor() : v(list_of(1)(2)) { } // ambiguous Any thoughts on this? Regards, Jens