If I had to guess they are probably sub-classing the built in collection classes under the covers to add in metadata slots for things like type information. As

If I had to guess they are probably sub-classing the built in collection classes under the covers to add in metadata slots for things like type information. As long as they implement the appropriate collections interface or class I don't see why they wouldn't be compatible with generics classes since none of type details ever makes it into the runtime.