Questions/issues regarding generators

Mark S. Miller erights at google.com
Sat Mar 30 06:13:30 PDT 2013


On Fri, Mar 29, 2013 at 6:21 PM, Allen Wirfs-Brock <allen at wirfs-brock.com>wrote:

>
> On Mar 7, 2013, at 11:05 AM, Andreas Rossberg wrote:
>
> On 7 March 2013 18:30, Allen Wirfs-Brock <allen at wirfs-brock.com> wrote:
>
> On Mar 7, 2013, at 7:37 AM, Andreas Rossberg wrote:
>
>
> 1) Are the methods of a generator object installed as frozen
>
> properties? (I hope so, otherwise it would be more difficult to
>
> aggressively optimise generators.)
>
>
> We discussed the factoring of the generator objects at the Nov 27 meeting.
>
> https://github.com/rwldrn/tc39-notes/tree/master/es6/2012-11 there is a
>
> sketch of the hierarchy we agreed to in in the notes
>
> https://dl.dropbox.com/u/3531958/tc39/generator-diagram-1.jpg
>
>
> TThe design I presented at the meeting is very close to that final one,
>
> answers this question, and is easier to read:
>
>
> http://wiki.ecmascript.org/doku.php?id=meetings:proposed_generator_class_hierarcy_nov_2013.png
>
>
> Ah, thanks. It seems that I missed that part of the meeting. I'll have a
> look.
>
>
> I created a more readable class hierarchy diagram based on the  above
> photo from the Nov. meeting.  This is what I'm using as my guide for
> putting generators into the spec. draft.
> The diagram is at
> http://wiki.ecmascript.org/lib/exe/fetch.php?cache=cache&media=harmony:es6_generator_object_model_3-29-13.png
>
>
> The most significant change from the meeting (and it really wasn't
> explicit on the whiteboard) is that generator prototypes don't have a
> "constructor" property that links back to its generator function instance.
>  In other words, you can't say:
>
> function * ofCollection() {for (i of collection) yield i};
> var itr1 = ofCollection();
> var itr2 = iter1.constructor();  //TypeError
>

That wouldn't be a type error. It would be invoking the value of the
inherited generator property.



>
> Allowing such constructor access seems like an unnecessary (and possibly
> undesireable) capability when you just passing generator instances around
> to be used as iterators.  Anybody disagree?
>
> itr1 instanceof ofCollection
>
> still works (subject to the usual instanceof caveats)
>
> Allen
>
>
>
>
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>


-- 
    Cheers,
    --MarkM
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