On Mon, Feb 16, 2015 at 7:35 PM, Brendan Eich <bren...@mozilla.org> wrote:
> Andreas Rossberg wrote: > >> On 16 February 2015 at 15:41, Andrea Giammarchi < >> andrea.giammar...@gmail.com <mailto:andrea.giammar...@gmail.com>> wrote: >> >> Common pattern is to poll.next() a yield until its `done` property >> is `true` so that a value can be used. >> >> This is I believe the common case that will create thousands of >> objects to be quickly trashed as garbage ... so I was wondering if >> those are all needed >> >> >> Er, I don't think this is the common use case at all. You iterate over >> something to process values, otherwise there isn't much point in using >> iterators in the first place. >> >> /Andreas >> > > Right. > > Instead of coming up with some bogo-API with a mutable singleton object > having pigeon-hole problems, how about engine hackers actually do some > optimizing? I remember in the Mosaic days, Eric Bina replied to someone who > decried the difficulty of fixing some ostensibly hard bug by writing the > patch. :-| > FWIW I have a patch pending in bug 1129313[1] that makes `for .. of` 4x as fast for Maps. That is without even having scalar replacement working yet, which probably explains why v8 is still 2x as fast. JSC is about 10% slower than patched SpiderMonkey. As explained in comment 12 of that bug, I haven't found a way to do the same thing - iterating over all entries (i.e., properties) and getting both key and value - anywhere nearly as fast on a plain object. That probably means I'm overlooking something, but at the very least I think the concerns about this being hard to optimize might be slightly overblown. [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1129313
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