[swift-evolution] [Pitch] Improving capturing semantics of local functions

[Wallacy]

Em ter, 14 de nov de 2017 às 17:02, Mike Kluev via swift-evolution <
swift-evolution at swift.org> escreveu:

> On Mon, 13 Nov 2017 22:30:25 +0100 David Hart <david at hartbit.com> wrote:
>
>> > On 13 Nov 2017, at 05:52, Slava Pestov <spestov at apple.com> wrote:
>> >
>> >> On Nov 12, 2017, at 8:11 PM, Brent Royal-Gordon via swift-evolution <
>> swift-evolution at swift.org> wrote:
>> >>
>> >> By analogy with the current closure syntax, the capture list ought to
>> go somewhere before the parameter list, in one of these slots:
>> >>
>> >> 1.   func fn<T>[foo, bar](param: T) throws -> T where T: Equatable { …
>> }
>> >> 2.   func fn[foo, bar]<T>(param: T) throws -> T where T: Equatable { …
>> }
>> >> 3.   func [foo, bar] fn<T>(param: T) throws -> T where T: Equatable {
>> … }
>> >> 4.   [foo, bar] func fn<T>(param: T) throws -> T where T: Equatable {
>> … }
>> >>
>> >> Of these options, I actually think #4 reads best; 1 and 2 are very
>> cluttered, and 3 just seems weird. But it seems like the one that would be
>> easiest to misparse.
>> >
>> > Another option that reads nicely IMHO is
>> >
>> > func fn<T>(param: T) throws -> T where T : Equatable [foo, bar] { … }
>> >
>> > I think #4 is ambiguous with array literals unfortunately.
>>
>
> adding to the list of options:
>
> 6. func fn<T>(param: T) throws -> T where T: Equatable [foo, bar] { … }
>
> otherwise +1 to #1 and to the one in proposal. also see about #4 below.
>
> plus, if 90%+ of use cases in practice would be [weak self] -- (the only
> examples shown in the proposals FTM) -- i would strongly consider this
> syntax sugar in addition to a generic notation:
>
> weak func fn<T>(param: T) throws -> T where T: Equatable { … }
>
> works with "unowned" as a bonus.
>
>
weak func  to imply [weak self] is a good idea.

weak func foo() {
  self?.bar();
}

unowned func foo() {
  self.bar();
}

Maybe this to:

onChange = weak { self?.bar() }

But we still have the problem using capture list.

And to avoid inconsistencies, I would leave the same way as the proposal.

 func local() { [weak self] in
            self?.bar()
        }


There's no perfect solution. And in this works fine today.



> if implement this sugar than some variation of #4 looks appealing to have
> these capture things close.
>
> Mike
>
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