On Apr 21, 2013, at 12:31 PM, Brendan Eich wrote:
> Allen Wirfs-Brock wrote:
>> On Apr 21, 2013, at 12:05 PM, Brendan Eich wrote:
>>
>>>>> What I mean is that:
>>>>> let obj = {__proto__: null}
>>>>> will always create an object whose [[Prototype]]
>>> Didn't you mean "an object whose property named '__proto__'" here?
>>>
>>>>> is null. Regardless of whether or not anybody has done:
>>>>> delete Object.prototype.__proto__.
>>>> Yes, that's what I just wrote!
>>>>
>>>> What part was unclear?
>>> Sorry, I misread your "[[Prototype]] is null" as "property named
>>> '__proto__' is null".
>>>
>>> But you cannot break ES5. Why are you changing things to deviate from it,
>>> never mind from ES6 consensus?
>>>
>>
>> We must be talking across each other...web reality is that
>> var obj = {__proto__: someObj};
>>
>> creates a new object whose [[Prototype]] is the value of someObj (assuming
>> it is valid for that use). Right?
>
> Argh, you're right. I'm wrong, the de-facto standard wants [[Put]] not
> [[DefineOwnProperty]] and that's what ES5 specified.
>
> I plead jetlag and throw myself on the mercy of the court!
Suspended sentence...and I really should be finishing preparing for my own
European speaking trip rather than being sucked into this dismal mess...
>
>> Doesn't that mean that ES5 implementations that support that semantics
>> already deviate from the ES5 spec which says that an own property named
>> "__proto__" should be created via [[DefineOwnProperty]]?
>
> That follows.
>
> However, let's get back to (a) coffee :-); (b) ES6 and the ability to delete
> Object.prototype.__proto__.
>
> You don't want that to affect object literals evaluated in the same realm
> after such a deletion. Why not?
Why should it? We already used the existence of {__proto__: whatever} got rid
of <| as declarative syntax for defining an object literal with a
[[Prototype]] other than object prototype. Making {__proto__: whatever} only
work some of the times means it isn't a reliable declarative syntax. Why would
we want to do that? There is arguably a good motivation wanting disable the
ability to dynamically __proto__ modify arbitrary pare-existing objects. But
what is the motifacation for doing that on newly created objects?
>
> SpiderMonkey at least goes out of its way to do [[Set]] (let's call it) not
> [[DefineOwnProperty]] for 'o = {__proto__: 42}', so why wouldn't [[Set]]
> create a fresh property, seeing nothing on Object.prototype named '__proto__'
> with a setter to run?
Because the semantics that says you can't use [[DefineOwnProperty]] may say to
go out of the way to do something else. It my strawman spec. it says use
[[SetInhertiance]] rather than [[Put]]. Either is a special case semantics and
[[SetInheritance]] is a much more direct expression of the likely user intent.
Allen
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