On Aug 21, 2013, at 7:46 AM, Erik Arvidsson wrote:
> On Wed, Aug 21, 2013 at 10:07 AM, Andreas Rossberg <[email protected]>
> wrote:
>> On 21 August 2013 15:41, Erik Arvidsson <[email protected]> wrote:
>>> One way to think of it is that the with is acting on a view of the
>>> object that does not have the blacklisted properties. This can be
>>> implemented using proxies. I'll leave that as an exercise.
>>
>> I see.
>>
>>>> * How would it interact with mutation?
>>>
>>> Another hole we didn't cover. Here is my proposal:
>>>
>>> The @@unscopable is only accessed once, when the object environment
>>> record is created.
>>
>> Hm, that would seem rather inconsistent with the way adding/removing
>> properties can dynamically change the domain of a 'with'. Consider:
>>
>> function safeenrich(o) {
>> o.a = 1
>> o[@@unscopable] = o[@@unscopable] || []
>> o[@@unscopable].push('a')
>> }
>>
>> let o = {}
>> let a = 0
>> with (o) {
>> a // 0
>> safeenrich(o)
>> a // 1
>> }
>
> I don't think it is worth covering these kind of new scenarios. We are
> patching a broken feature here.
>
> Still, it is easy to allow that if we really wanted to. We can make
> ObjectEnvironment [[HasBinding]] do object.[[Get]](@@unscopeable)
> every time then.
@@unscopable and its interaction with the with state is specified in the ES6
draft that I will release this weak
It is specified as Erik describes, @@unscopable is only access when a with is
entered. The computability use case was designed to support doesn't involve
dynamically adding properties to a with object. Instead, the problem is
inherited properties of the with object shadowing out scope bindings.
It's possible to opt-out of the mechanism via:
Object.mixin( withobj, { [@@unscopable]: [] });
with (withobj) {
for (v of values()) ...
}
Allen
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