On Mar 14, 2011, at 3:02 AM, Dmitry Soshnikov wrote:
> Yep, thanks Brendan,
>
> I filed the bug https://bugzilla.mozilla.org/show_bug.cgi?id=641436
>
> But the thing with `this` is still interesting for me. So in this particular
> case `this` should be set to `undefined`.
No, |this| is not set to undefined. The generator function yields undefined
each time (via |yield;| in the loop body).
That undefined is what the anonymous expression closure you pass to map should
(absent the bug) return in turn (i.e., undefined is the return value of
g.next() and thus the return value of function(i) g.next()).
Notice how you evaluate a |new| operator exactly once, in the top-level
assignment expression statement:
>> // infinite objects generator
>> let g = new function () {
>> this.x = 10;
>> while (true) {
>> yield;
>> }
>> };
>>
>> // generate an array of 3 objects
>> let objects = [1, 2, 3].map(function(i) g.next());
A generator function called as a constructor via new receives a fresh Object
instance as |this|, same as for any function.
However, there's no way for a generator function to return that instance,
because a generator function always implicitly returns a fresh generator
iterator when invoked. It could store |this| in the heap, and whatever value
|this| receives is saved as part of the shallow continuation capture by the
generator.
If you write |return this| anywhere in the body of the generator function
you'll get an early error. So really all |new| is doing for you here is giving
a fresh object to |this|, which seems fine if that's what you want.
/be
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