Currently, there are a number of places in the code where pointer values are stored using instances of the RexxInteger class. This causes problems with 64-bit type safety because it assumes that integer values and pointers are interchangeable. This is no longer true. A real, immutable pointer class should be implemented. This should only be instantiable via internal usage, but the instances also need to be well behaved for situations where they can "leak" out to external code. This would also be useful for returning things like window handles, etcs, since they will be in a common format that is easily converted back into a pointer value.
Most of the oode for doing this exists in the 4.0 code base.