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

[Mike Kluev]

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.

Mike
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