See also https://bugs.ecmascript.org/show_bug.cgi?id=3246#c3 I think the behavior where a data property can be installed accidentally under an accessor property is crazy, but looks like I was overruled.
Dmitry On Tue, Apr 21, 2015 at 4:18 AM, Caitlin Potter <[email protected]> wrote: > 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]> > 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]> > 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]> 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] >> 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] > https://mail.mozilla.org/listinfo/es-discuss > > > > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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