On 14 Aug 2010, at 23:58, Mark S. Miller wrote:
> On Sat, Aug 14, 2010 at 3:16 PM, Erik Arvidsson <erik.arvids...@gmail.com>
> wrote:
> I think Ash brings up a valid point here. From a usability point it is
> a clear win to use [], delete and in for WeakMaps and Maps.
>
> We've been over this territory before. How would you reconcile this (quite
> sensible) desire with the existing semantics of [], delete, and in, and with
> the existing code that depends on this semantics?
>
> Another pain point is implementation cost on uninvolved code. I had earlier
> proposed a change to Proxy semantics to achieve exactly this. (Because,
> again, I do find the idea desirable.) It failed because it would have
> required postponing the coercion of an index from object to string until one
> knew the type of object one was indexing into. IIRC, this was not free for
> uninvolved code on some implementations. I'm rather confident that any new
> feature that slows down code not using that feature will fail to achieve
> consensus.
>
> If a painless reconciliation can be found, I'd probably be supportive.
> Suggestions welcome.
Okay I can see (from an implementation PoV if not usability) why |[]|, |delete|
and |in| can't work, but is there anything that says the Object.keys has to
return strings and can't just return an array of Objects for a WeakMap? Not
sure if this makes the Object MOP layer cleaner or not...
-ash
>
>
>
> On Sat, Aug 14, 2010 at 14:02, Mark S. Miller <erig...@google.com> wrote:
> > On Sat, Aug 14, 2010 at 1:01 PM, Ash Berlin <ash...@firemirror.com> wrote:
> >>
> >> On 14 Aug 2010, at 07:22, Erik Arvidsson wrote:
> >> > I have a few questions regarding the WeakMap API.
> >> >
> >> > 1. Why isn't there a way to check for presence of a key (using
> >> > has/contains)?
> >> >
> >> > Given that undefined is a valid value it is not sufficient to just
> >> > return undefined for get
> >>
> >> Does the standard trick of:
> >>
> >> if (key in weakMapInstance) { }
> >>
> >> not work?
> >
> > It does not. A key is not a property name. A weak map is an object with two
> > own properties, names "get" and "set", whose values are the methods that
> > constitute the weak map API.
> >
> >>
> >> >
> >> > 2. Why isn't there a way to remove a key-value-pair?
> >> >
> >> > Setting the value to undefined is not the same.
> >>
> >> Again:
> >>
> >> delete weakMapInstance[key];
> >
> > No. This syntax deletes named properties.
> >
> >>
> >> > 3. Why isn't there a way to iterate over the keys?
> >> >
> >> > I can see that this might be a security issue but iteration is useful
> >> > and security sensitive code can prevent iteration in several ways.
> >>
> >> Object.keys(weakMapInstance)
> >
> > No. Object.keys enumerates property names.
> >
> >>
> >> >
> >> > 4. Why does set throw if the key is not an object but get doesn't?
> >> >
> >> > Same would go for delete and has if those are added.
> >>
> >>
> --
> Cheers,
> --MarkM
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