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' thinkthi s idiom could be taken advantage of in a possible implementation of a dynamic multi-index container.