Iterators, generators, finally, and scarce resources (Was: April 10 2014 Meeting Notes)

Mark S. Miller erights at
Wed Apr 30 07:03:27 PDT 2014

I don't think I understand the issue. AFAICT, all the system implemented
iterators don't need to clean up anything that's not already cleaned up by
GC, so they wouldn't need a .return method anyway. Is there a

On Wed, Apr 30, 2014 at 3:48 AM, Andreas Rossberg <rossberg at>wrote:

> On 29 April 2014 20:35, David Herman <dherman at> wrote:
> > On Apr 29, 2014, at 12:40 AM, Andy Wingo <wingo at> wrote:
> >> Indeed I expect that in
> >> practice most iterators in an ES6 program will be map, set, and array
> >> iterators, which in practice will not be implemented with generators.
> >
> > I strongly disagree with this. Generators will by far be the most
> convenient and common way to implement iterators, regardless of their data
> source.
> Yes, but Andy was talking about VM-provided iterators, where
> convenience of implementation does not matter. It is safe to assume
> that for all VMs a generator-based implementation will be
> substantially more expensive than a hand-written one (and will remain
> so in the foreseeable future, I'm pretty sure of that -- e.g. inlining
> is tricky for generators). So VM implementers won't use generators
> internally.
> /Andreas

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