Right, good point. No need to care about `existingDescriptor.[[Get]]` or `existingDescriptor.[[Set]]`
> On Apr 20, 2015, at 10:12 PM, Allen Wirfs-Brock <[email protected]> wrote: > > > On Apr 20, 2015, at 6:52 PM, Caitlin Potter 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) >> >> 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. > > `ownDexc` refers to the property descriptor of the [[Prototype]] in this case > and if "super.prop is an accessor" that will be an accessor property > descriptor. That falls throw steps 4 and 5 and eventually invokes its setter > in step 9. The Receiver (the original `this` value only is involved as the > `this` value passed in the call to the setter. > > Allen > > > > > > > > > >> >>> On Apr 20, 2015, at 9:37 PM, Allen Wirfs-Brock <[email protected] >>> <mailto:[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 >>>> >>>> >>>> _______________________________________________ >>>> es-discuss mailing list >>>> [email protected] <mailto:[email protected]> >>>> https://mail.mozilla.org/listinfo/es-discuss >>>> <https://mail.mozilla.org/listinfo/es-discuss> >>>> >>>> >>>> >>>> >>>> -- >>>> Text by me above is hereby placed in the public domain >>>> >>>> Cheers, >>>> --MarkM >>> >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] <mailto:[email protected]> >>> https://mail.mozilla.org/listinfo/es-discuss >>> <https://mail.mozilla.org/listinfo/es-discuss> >> >
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