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[Python-Dev] sizeof(long) != sizeof(void*)

Tim Peters tim.one at comcast.net
Wed Aug 6 22:23:02 EDT 2003 
[Samuele Pedroni]
> care to suggest a cheap way to get such a unique integer that's
> not the address.

I'd love to, but don't know enough about Java to guess.

> ...
> otherwise I see no other way than keeping a weak identity mapping
> from objects to integral type values, the aforementioned unique
> integers.

Then is there a reason not to do that?  Presumably only objects to which
id() is actually applied need to become keys in such a mapping, and if so
only id() users pay the price.

> Likely using a type for which a counter to get fresh unique
> integers cheaply will not overflow too quickly.

If it's a weak-keyed dict you could also reuse the integer values associated
with keys that go away.

> Or instead of the mapping attach such integrals value to each
> object. The latter is not an option for Jython, because we cannot
> attach things to general Java objects we have to deal with.

Then why bring it up <wink>?

Note that I don't object to introducing a mechanism that copy etc can use
that's highly efficient under all implementations.  But the introduction of
such a mechanism isn't sufficient reason to get rid of the current id(),
even if id() is horridly expensive in some implementations.
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