[swift-evolution] extend trailing closure rule

[Saagar Jha]

How about using a colon to separate it, to make `completion` look like an
argument and to separate it from being a function? Something like this:

UIView.animate(withDuration: 0.4) {
// animations
}
completion: { finished in
// completion
}


On Thu, Jun 9, 2016 at 1:06 AM Brent Royal-Gordon via swift-evolution <
swift-evolution at swift.org> wrote:

> > Here's a common thing to say:
> >
> >    UIView.animate(withDuration:0.4, animations: {
> >        self.v.backgroundColor = UIColor.red()
> >    })
> >
> > That's ugly. I'd rather write:
> >
> >    UIView.animate(withDuration:0.4) {
> >        self.v.backgroundColor = UIColor.red()
> >    }
> >
> > What stops me is that `animations:` is not eligible for trailing closure
> syntax, because it isn't the last parameter — `completion:` is. But
> `completion:` has a default value, namely `nil` — that's why I'm allowed to
> omit it. So why can't the compiler work its way backwards through the
> parameters, and say to itself: "Well, I see a trailing closure, and I don't
> see any `animations:` label or any `completion:` label, so this trailing
> closure must be the `animations:` argument and the `completions:` argument
> must be `nil`."
>
> If we may take leave of practical considerations for a moment, I'd like to
> note that the ideal syntax for a call like this would probably look like:
>
>         UIView.animate(withDuration: 0.4) {
>                 // animations
>         }
>         completion { finished in
>                 // completion
>         }
>
> And of course, since `completion` has a default value, this would
> naturally degrade to:
>
>         UIView.animate(withDuration: 0.4) {
>                 // animations
>         }
>
> I'm guessing this isn't possible because the `completion` could instead be
> a call to a separate function with a trailing closure. But is there some
> way we could get something similar? That could significantly improve our
> handling of multi-block APIs and give trailing closures the ability to
> emulate more kinds of syntax.
>
> --
> Brent Royal-Gordon
> Architechies
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
-- 
-Saagar Jha
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160609/245ed1d3/attachment.html>