Supporting ES6 iterables in collection methods

[tgriesser]

So this sounds like something lodash isn't going to support yet because it will add quite a bit of code lodash/lodash#737 - but I think it'd be cool to have a ticket here to explore the possibility/implications (code, performance, and otherwise) of supporting ES6 iterables in at least the collection functions of underscore.

As ES6 Map / Set are available in more places (latest browsers, babel polyfill) it'd be great to be able to iterate in the same way as objects, especially since Map it avoids the weird edge cases of treating an object as a Map (__proto__, ownProperty checks, etc.). Also, the ES6 iterator API provides a standard convention for iterating arbitrary objects and it'd be great if underscore could maybe act as a functional api for-of in the same way it does for for/for-in

I feel like it should be possible to come up with a way that does this in most reasonable cases with out too much overhead, but I admittedly haven't explored it too in-depth - just wanted to see if anyone else would be interested in discussion.

[jashkenas]

Would certainly be worth exploring in a pull request. Would it really be so much code? You couldn't put the iteration logic in a single function? ES6 for of is atrociously slow as is, so it seems like it would be hard to do worse?

[jdalton]

Related to lodash/lodash#1420, _#next could be a way to get the ball rolling.

[jgonggrijp]

See also discussion in #2808.