For C++
If you are referring to ie an AbstractFactory I think that a registerCreatorFunc(..) method usually is better than requiring to add a case for each and every "new" statement that is needed. Then letting all classes create and register a creatorFunction(..) which can be easy implemented with a macro (if I dare to mention). I believe this is a common approach many framework do. I first saw it in ET++ and I think many frameworks that require a DECL and IMPL macro uses it.
