Hi list, I'm looking for a "multi-class container", with access to sub-containers of elements depending on their class. All elements are derived from the same base class, and I want to have "views" of containers of final classes, or even intermediate classes. This container would be associative, like a map. As instance if I have // Base class class A {} ; // Intermediate classes class B : public A {} ; // Final classes class C : public B {} ; class D : public B {} ; class E : public A {} ; I want a container that can hold any A-derived class, on which I could have views of sub containers of class C, D or E, and even a sub container of intermediate class B. I looked at multi-index, but no such feature seems to be feasible. And I have no need of multiple indices, as I access all theses elements by their ID which is a member of A. Any hint on how I could implement this? Cheers, SeskaPeel.