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

[Mike Kluev]

On 14 November 2017 at 19:02, Mike Kluev <mike.kluev at gmail.com> wrote:

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

the closer we have it to this English sentence the better IMHO:

weak throwing function "fn", capturing "foo" and "bar" weakly, using
generic type "T" which is "Equatable", having parameter "param" of type
"T", returning type "T", with the following body { ... }

Mike
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20171114/55484af4/attachment.html>