[boost] [mpl] sequence details

Hi, What is the best way to convert the result of a mutating mpl intrinsic metafunction (such as 'mpl::push_back', for example) to numbered form ('vectorN<a1,a2,..>') ? I tried using the type-member (which only works on some compilers - not with GCC for example) and figure 'copy' could probably do the trick (but is a quite complex operation) so there might be a better recipe for this. In a library I'm currently working on, I use a decorator pattern to make a class model of a sequence it holds (i.e. give it a tag type member and specialize *_impl with delegate semantics). After applying the delegate metafunction I need the sequence in a form I can match with partial specialization. Thanks for your help, Tobias