On 12/3/2010 6:15 PM, James Y Knight wrote:
On Dec 3, 2010, at 6:04 PM, Terry Reedy wrote:
gc is implementation specific. CPython uses ref counting + cycle
gc. A constraint on all implementations is that objects have a
fixed, unique id during their lifetime. CPython uses the address as
the id, so it cannot move objects. Other implementations do
differently. Compacting gc requires an id to current address table
or something.
I left out that the id must be an int.
It's somewhat unfortuante that python has this constraint, instead of
the looser: "objects have a fixed id during their lifetime", which is
much easier to implement, and practically as useful.
Given that the only different between 'fixed and unique' and 'fixed' is
the uniqueness part, I do not understand 'practically as useful'.
Duplicate ids (in the extreme, that same for all objects) hardly seem
useful at all.
--
Terry Jan Reedy
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