If I understand that correctly, then I think I'd prefer to just keep a separate hash of "signatures" for objects as they arise. The object can go out of scope, be destroyed, be overwritten, who cares... I keep an MD5 or checksum of some sort based on the object's content, and if another object arises with the same signature, I have firm and simple proof of the "deja vu", without having to worry about what happened to (de|re)allocated memory since a given object was last seen.