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Subject: Re: Associating metadata with non-objects
From: Charles Lowell <cowb...@thefrontside.net>
To: v8-users <v8-users@googlegroups.com>
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On May 3, 11:35=A0am, Stephan Beal <sgb...@googlemail.com> wrote:
> On Tue, May 3, 2011 at 3:41 PM, Charles Lowell <cowb...@thefrontside.net>=
wrote:
>
> > into Ruby like Context and FunctionTemplate. That said, being able to
> > get a stable, unique object id for all values would be killer. You
> > mentioned that it would be relatively straightforward to roll your
> > own? Any chance you could elaborate?
>
> For OBJECTS you can presumably use the identity hash, but for non-Objects=
 v8
> does not publish a _stable_ unique ID. You can get a (void *) to the
> underlying data (Value::Data(), IIRC), which could then be used as a key,
> but that address is not guaranteed to be stable - v8 may relocate it as a
> side-effect of allocation/gc.
>
> When i first started porting my SpiderMonkey JS/C++ type conversions
> framework to v8. that lack of a stable ID was my first big hurdle, and
> eventually gave up on the idea that one can tie a (T*) to a JS integer in
> v8.
>
> For builtin Object types (Date, Regex, etc) you can't stuff your own
> mappings into them because the number of internal fields is defined by th=
e
> Template and not on a per-instance basis. e.g. the Regex authors didn't s=
et
> aside an internal field for our use then we cannot stuff an internal fiel=
d
> in those instances.
>

Indeed, but Mads mentioned at the very end of his response that there
was a way to roll your own for values, and I'm curious to hear what he
had in mind.

cheers,
Charles


> --