On Tue 11 Jun 2013 11:08, Axel Rauschmayer <[email protected]> writes:
> The idea that iterators return themselves from their @@iterator > (__iter__) hook has years of actual programmer mileage in Python. I > take that experience seriously, compared to arguments from purity > that tax the common use-cases. > > I’d be happy with either solution, but let’s compare: > > AFAICT, the tax is on for-of (and Array.from()): they need to > additionally check whether an object is an iterator. So, my proposal would be to make the for-of RHS expect an iterator, and remove the concept of "iterable". So there's no need to check for anything; you just assume you have an iterator. I don't find the cost of this change (let's not say "tax" ;) terrible: for (x of y.values()) f(x); Or for (x of values(y)) f(x); Though the former seems more javascripty, my impression was that we were not adding more prototype methods, in favor of using modules instead. I don't have a @horse_js in that race though. The reason I think this is OK is because: for (x in y) f(x) translates as for (x of keys(y)) f(x) so to me it is natural that values should also come from a function/method call: for (x of values(y)) f(x) As iterators and for-of become more prevelant, I think there are actually few times that you want the default iterator -- the reason being that you will deal more with iterators and less with reified containers like arrays. The evolution of Python seems to show this, and (dare I mention it?) Dart also seems to be going in this direction. So that's the "cost" side. The benefit of expecting the RHS to be an iterator is that itertools-like combinators become easier to write, and that can only be a good thing, as we avoid making intermediate garbage containers and eager computation. As a side benefit, we could remove the concept of "iterable" from the spec. Also we remove the opaque @@iterator call from for-of, which can have better error-reporting characteristics. Again, MHO :) Cheers, Andy _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
