Thank you for the suggestion Ben!
On Tuesday, November 10, 2020 at 5:14:35 AM UTC-5 Ben Noordhuis wrote:
> On Tue, Nov 10, 2020 at 4:54 AM jres...@gmail.com <jres...@gmail.com>
> wrote:
> >
> > I would like to cache Persistent handles in such a way that I can
> retrieve the same Persistent instance given the identical JS object, i.e.
> imagine a function like so:
> >
> > Persistent<Object> GetPersistentForObject(Local<Object> obj)
> > {
> > // If we have already created a Persistent for obj, find and return it.
> > // Otherwise, create and return a Persistent for obj and cache it for
> > // future calls.
> > }
> >
> > The obvious thought is to store the Persistent handles in a map of some
> kind, but what to use as the key? I assume it would not be possible to
> actually use Local handles as keys in a map that outlives the current
> HandleScope.
> >
> > One thought I had was to assign a unique integer to the object using
> obj.SetPrivate(...), and use that as the key, but SetPrivate is documented
> as experimental, which is discouraging.
> >
> > Is there an easier way to achieve what I'm trying to do? I feel like I
> may be missing something obvious...
> >
> > Jonathan
>
> A hashmap should work if you observe the following;
>
> 1. Use `v8::Object::GetIdentityHash()` to compute the hash key.
> 2. Use `Persistent::operator==()` to detect duplicates (also has an
> overload that compares against a Local)
>
> I.e., step 1 is to find the right bucket and step 2 is to find out if
> that bucket already contains the object.
>
> Using just the identity hash isn't sufficient, see [1] and [2] for
> discussion.
>
> Caveat: use `v8::Value::SameValue()` - not `Persistent::operator==()`
> - if you also store primitives (numbers, strings, etc.)
>
> [1] https://github.com/denoland/deno/pull/7946#discussion_r504192165
> [2] https://github.com/denoland/deno/issues/7969
>
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