lexical for-in/for-of loose end

Herby Vojčík herby at mailbox.sk
Sun Feb 5 04:45:18 PST 2012


Grant Husbands wrote:
> Herby Vojčík wrote:
>>> Your proposal depends on being able to reassign variable pointers, but
>>> they don't necessarily exist.
>> Well, references are all over the spec (or were in times of ES5).
>
> What I was calling activation records, the spec calls environment
> records and it does not, by my reading, imply that variables within
> them are reference-like in nature (read clause 10.2). However, we
> don't need to argue this point.

I feel like misunderstood. I _know_ there aren't ref variables in the 
spec. I never told that. I was just telling that 'i' inside the loop 
body may be compiled not as "Ref(loop-body-record, 'i')" whenever it is 
accessed/modified (and optimized when Ref is not really needed, but you 
can see at it as if it is always Ref to local i), but as 
"Ref(the-record-to-use, 'i')", the-record-to-use being local variable in 
loop iteration which can change its value (it can be outer-record when 
loop runs, at it can be local-record when iteration ends and values are 
fixed in local 'i').

>>> Or, here's one that copies the other way (and is probably cleaner):
>>> 'Note' all closures (dynamically) created in (lexically,
>>> post-desugaring) the loop body. Each time you end an iteration, update
>>> all the loop variable activation record pointers to point at a new
>>> clone of that activation record.
>> If I understood correctly, this is what I proposed. Or maybe it only looks
>> like it?
>
> It has the same behaviour, but without needing variable pointers; that
> was the idea. I now propose it to the list as a variant of your idea
> that I think some may prefer. I'm merely trying to make sure your idea
> gets the attention it deserves.

Thanks. Yes it is the same behaviour, the active loop body always uses 
the same shared 'i', only async closures get the fixed copy. Nice.

> To be completely acceptable, the mechanics would need fleshing out, of course.
>
> Regards,
> Grant.

Herby


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