>>If the prop property accessed by super.prop is an accessor, super.prop = x;
>>should invoke its setter. super.prop should invoke its getter.
>It does. This is about what happens when that property is a data property
>doesn't exist. What happens when we do
>[[HomeObject]].[[GetPrototypeOf]]().[[Set]]('prop', x, this)
I don’t think the accessor case does work. `ownDesc` never refers to the
property descriptor of the receiver when O[P] is a SuperReference, so if
there’s an `this.prop` is an accessor, and `super.prop` doesn’t exist, the data
descriptor path is taken.
> On Apr 20, 2015, at 9:37 PM, Allen Wirfs-Brock <[email protected]> wrote:
>
>
> On Apr 20, 2015, at 6:21 PM, Mark Miller wrote:
>
>> If the prop property accessed by super.prop is an accessor, super.prop = x;
>> should invoke its setter. super.prop should invoke its getter.
>
> It does. This is about what happens when that property is a data property
> doesn't exist. What happens when we do
> [[HomeObject]].[[GetPrototypeOf]]().[[Set]]('prop', x, this)
>
> Allen
>
>
>
>
>
>
>
>
>
>>
>> On Tue, Apr 21, 2015 at 4:18 AM, Allen Wirfs-Brock <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> On Apr 20, 2015, at 12:39 PM, Jason Orendorff wrote:
>>
>>> On Mon, Apr 20, 2015 at 12:44 PM, Allen Wirfs-Brock
>>> <[email protected] <mailto:[email protected]>> wrote:
>>>>> In the spec, 9.1.9 step 4.d.i. is where `super.prop = 2` ends up, with
>>>>> O=X.prototype.
>>>>
>>>> 4.d.1 doesn't set the property, it just comes up with the property
>>>> descriptor to use, if the `Receiver` does not already have a corresponding
>>>> own property.
>>>>
>>>> 5.c+5.e checks if the corresponding own property actually exists on the
>>>> `Receiver`.
>>>>
>>>> If it already exits then it does a [[DefineOwnProperty]] that only
>>>> specifies the `value` attribute. This should respect the current
>>>> `writable` attribute of the property and hence reject the attempt to
>>>> change the value.
>>>
>>> I agree with all of this, except I don't see where the attempt is
>>> rejected. Since the property is configurable, I think
>>> [[DefineOwnProperty]] succeeds.
>>>
>>> The property is still non-writable afterwards. Only the value changes.
>>>
>>> So this isn't breaking the object invariants: the property in question
>>> is configurable, so it's OK (I guess) to change the value. It's just
>>> surprising for assignment syntax to succeed in doing it.
>>
>> I think it's bogus and needs to be corrected. Not only does it allow (in
>> weird cases for [[Set]] (ie, assignment) to change the value of a
>> non-writable property. It also means there are cases where [[Set]] will
>> convert an accessor property to a data property.
>>
>> In combination, I think this is a serious bug that needs to be fix in the
>> final published ES6 spec. The fix I propose is in 9.1.9 to replace Set 5.e
>> as follows:
>>
>> 5.e If existingDescriptor is not undefined, then
>> i. If IsAccessorDescript(existingDescript), return false.
>> ii. If existingDescriptor.[[Writable]] is false, return false.
>> iii. Let valueDesc be the PropertyDescriptor{[[Value]]: V}.
>> iv. Return Receiver.[[DefineOwnProperty]](P, valueDesc).
>>
>> Lines 5.e.i and 5.e.ii are new additions.
>>
>> Thoughts?
>> Allen
>>
>>
>> _______________________________________________
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>>
>>
>>
>>
>> --
>> Text by me above is hereby placed in the public domain
>>
>> Cheers,
>> --MarkM
>
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