-----Original Message----- From: boost-bounces@lists.boost.org on behalf of Peter Dimov I need to warn you that there is very little chance for your patch to be accepted in this form. Extending _bi::listN (I'd suggest making them conforming MPL or fusion sequences) needs to be done non-intrusively and in a separate header. ------ Hey Peter, I'm almost there doing it this way, but I gotta tell you that it requires generating code (attached) as you need lots of partial specializations. The reason is that there isn't one type but N types. Consider getting the type of the element at index I. Of course, even with changing to some other tuple as the underlying, I think you'd have to generate code (who would want to write it out by hand?!). Does that sound sensible or totally wrong? Sohail PS: It is pretty easy to extend fusion, I must say!