On Apr 25, 2014, at 10:25 AM, Oliver Hunt wrote:
>
> On Apr 25, 2014, at 4:24 AM, Andreas Rossberg <rossb...@google.com> wrote:
>
>> The way destructuring assignment currently is specified leads to
>> rather inconsistent evaluation order. Consider:
>>
>> let o = {}
>> function f() { print(1); return o }
>> function g() { print(2); return 5 }
>>
>> f().x = g() // 1, 2
>> {a: f().x} = {a: g(}} // 2, 1
>>
>> That is, destructuring assignments violate the left-to-right
>> evaluation that is otherwise maintained.
>>
>
> I don’t believe that there is any reason to break from left-to-right
> evaluation order. Even if it was uncommon it’s still an unnecessary hazard.
>
> Spec bug maybe?
Nope, it's always been designed this, going back to the original wiki strawman
http://wiki.ecmascript.org/doku.php?id=harmony:destructuring#semantics and I
assume the original FF implementation.
It has also been something that we has been discussed here and in TC39 multiple
times. If we wan to revisit this decision we really need to dredge up all of
those previous discussions to see if there is new data that would cause us to
change this decision.
Basically for destructing assignment, each property element can be an arbitrary
assignment expression and all of their Reference values would have to be saved
to get left to right order.
Allen
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