arrows and a proposed softCall
herby at mailbox.sk
Tue Jun 5 11:34:18 PDT 2012
Angus Croll wrote:
> Yes the thread needs wrapping up. Maybe I can attempt summarize the
> dilemma - with a question:
> Is call/apply just a remedy for non-lexical this assignment? Or is it a
> powerful feature in it own right.
> I'm with the second camp, but I think I'm in the minority in this list
The second, of course :-)
> On Tue, Jun 5, 2012 at 10:23 AM, Brendan Eich <brendan at mozilla.com
> <mailto:brendan at mozilla.com>> wrote:
> Russell Leggett wrote:
> On Tue, Jun 5, 2012 at 12:36 PM, Brendan Eich
> <brendan at mozilla.com <mailto:brendan at mozilla.com>
> <mailto:brendan at mozilla.com <mailto:brendan at mozilla.com>>> wrote:
> What I perceive from the JSFixed effort, and from Angus who is
> good enough to post here: people have a particular concern that
> fat-arrow is too sweet and it will lure the children into the
> witch's house: passing fat arrows to dynamic-this APIs.
> We have data suggesting that fat arrows address the dominant
> use-case, thanks to Kevin Smith and others. So fat arrows are in
> ES6, well and good.
> I think the particular concern about => being an attractive
> nuisance for some APIs such as Angus's mixin combinators, which
> rely on .call overriding |this|, can be addressed by adding ->
> too. Angus agrees, but -> is not on the boards for ES6 (yet).
> We could try to revive ->, but first, we should face the
> attractive nuisance argument squarely, instead of dancing around
> it with isBound abuses that try to "catch fat arrow going
> into the
> witch's house".
> I think that with ->, a similar problem will still crop up -
> specifically that => will be the more common use, and then in
> the rare case that -> is needed, people may still use =>.
> I agree. The problem we'll then see is anxiety over "which arrow?"
> -- the Paradox of Choice (Schwartz).
> Do we still need isBound to catch that error as well? Even with
> the choice of -> or =>, the person writing the code has to know
> which one to use and why. That means they have to understand the
> whole dynamic |this| problem.
> Agreed, so (while we are spiraling, no worries) this helps. We
> cannot remove the dynamic vs. bound |this| choice from JS. But we
> can avoid adding choice when shortening, based on use-case frequency
> analysis. This, we have done (many thanks to Kevin Smith again), and
> it is why => got into ES6.
> I think that the dynamic |this| behavior of jQuery is not
> something that should be encouraged. I understand it is probably
> mostly that way because of the dom event api,
> JQuery goes further, I think simply due to mimesis. The DOM binds
> |this| to the event target but in the context of the old DOM level
> 0, where the only way to attach an event handler was as a method of
> the target, this was not "wrong". JQuery goes much, much further
> down the path to crazy |this| dynamic binding.
> but that doesn't change the fact that it really has a bad smell
> to it.
> On this everyone agrees. No disrespect to JQuery, but it is
> important to know what *not* to imitate. We know now, so we
> shouldn't be using JQuery as a rationale for dynamic-this short
> forms or isBound as a general tool.
> CoffeeScript has ->, but if you look at the examples, none of
> them actually make use of dynamic |this| except for methods, and
> we're adding a nice method syntax, so it isn't really needed.
> Method syntax, and => should cover the majority of cases and
> lead people down the right path.
> This is the current ES6 state and rationale, indeed.
> I know this is going around in a circle, but my point is that
> adding -> doesn't fix the problem, which is devs not knowing
> when to use => and when to use function.
> It's a good point. I hope we can wrap this thread up. It has been
> helpful to disclose or emphasize the situation:
> 1. "soft-bind" breaks abstractions and won't fly with implementors.
> 2. isBound needs more discussion but it too breaks abstractions and
> it must be defined (Mark's definition) to work for all
> this-insensitive functions.
> 3. => covers the dominant use-case for functions not using |this|
> and functions capturing lexical |this| via .bind or var self=this.
> 4. Adding -> doesn't avoid confusion over whether to use => or
> function, it only adds a shorthand -- good for those who want this
> -- and at the same time (the paradox of choice) creates anxiety over
> "which arrow do I use?".
> We could add isBound. We could add -> too. Right now ES6 has =>
> only, based on a weighting of the costs and benefits in 1-4.
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