thanks, i will have a look at that, too. i thought in inside out objects attributes are stored in hashes with the object (stringified) as a key. that would be an extra hash lookup.
edit: ah, a sequence number can be used for the id of an object. seems this could be what i want (edit2: although O::IO does way more than i need, and actually in some cases i might not want to use inside-out objects.)