Maybe by reifying the indirection? The compacting arena would hand out smart pointers which would either always bounce through something (to get from an indentity to the actual memory location, at a cost) or it'd keep track and patch the pointers it handed out somehow.

Possibly half and half, I don't remember what language it was (possibly obj-c?) which would hand out pointers, and on needing to move the allocations it'd transform the existing site into a "redirection table". Accessing pointers would check if they were being redirected, and update themselves to the new location if necessary.

edit: might have been the global refcount table? Not sure.

It would be possible (and not that hard) for Copy types, but you'd need some custom derive traits if you had any pointers to managed objects.