Allow me to repost this, since given the current traffic in the list it could well have passed unnoticed. Is (the proposed) Boost.Interfaces lib able to handle the following scenario? template<typename T> interface IIterator { T& operator*()const; ... }; template<typename T> interface IContainer { IIterator<T> begin(); IIterator<T> end(); ... }; It is not the issue of specifying an operator as part of the interface IIterator (this'll be taken care of in the future according to the docs), but the fact that IContainer::begin is required to return an object implicitly convertible to IIterator<T>. Can Boost.Interfaces do that? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo PS: Just for motivation, I' think this idiom could be taken advantage of in a possible implementation of a dynamic multi-index container.