[Boost-users] [mpl] how to create a map using an algorithm

Lets say I have several types t1, t2, t3, and so on. Each of them has a typedef x within it. I want to be able to get a type y, and find the type t which holds is_same. I thought of doing it using mpl::map< pair, pair, ...>. The problem is how to create the map. I can create it manually, just like in the previous sentence, but I hope there's a better way. Is there some transform algorithm that I can pass it an mpl::set and a meta-function that yields t::x for any given t, and this algorithm would produce the desired map? Thanks, Yuval