> The problem of doing GC on arbitrary binary structures is sticky too.

Perhaps it is best not to attempt to GC arbitrary binary structures.  It
seems to me that could be very dangerous.  Not all external systems will
behave like COM, and external systems may have some screwball data
structures.  A ridiculous example, but one that illustrates such difficulty,
is one where pointers are stored with their bits inverted.  To actually
retrieve the referenced information, you must first invert the bits.  How
could you design a system that could effectively perform GC in such
circumstances?

My believe is that this is best left up to the user of the external system.
With adequate support from GC, they could add their own custom GC (by
hooking into the Smalltalk GC) for resources associated with the external
system.

- Stephen