Re: Object identity

[Lars Brinkhoff]

Barry Margolin <barry.margolin@level3.com> writes:
> Lars Brinkhoff  <lars@nocrew.org> wrote:
> >Is there a function, say object-identity, in Emacs Lisp that maps an
> >object to a unique value (other than the object itself)?  For example,
> >the value could be an integer, or a list of integers, or a string,
> >that represents the memory address of the object.
> I'm not sure it's possible to write such a function without significant
> overhead.

Right, I didn't consider that garbage collection (in general) can move
things around.

Stefan Monnier <monnier@iro.umontreal.ca> writes:
> > The OP explained what it's useful for: emulating weak hash tables in a
> > system that doesn't have them built in.
> That's not how I understood his article.  He seemed to say that he
> currently uses an implementation of object-identity which relies on
> a weak hash-table but that his Emacs's doesn't implement weakness.

Right, that's what I meant.

> I.e. he seemed to say he needed weak hash-tables to implement
> oject-identity, not the other way around.

Well, either I need weak hash tables, or a different implementation
of object-identity.

-- 
Lars Brinkhoff,         Services for Unix, Linux, GCC, HTTP
Brinkhoff Consulting    http://www.brinkhoff.se/