[swift-evolution] [Pitch] Make the first parameter in a function declaration follow the same rules as the others

[Brent Royal-Gordon]

> Our accepted naming guidelines have embraced first argument labels for functions and methods. This weakens our justification for making the first parameter declaration in a `func` declaration behave differently from the others, implicitly being unlabeled. It seems pretty clear to me we should make all of the parameter declarations behave uniformly:
> 
> func foo(x: Int, y: Int) // Should declare foo(x:y:), instead of foo(_:y:)
> func foo(_ x: Int, y: Int) // Explicitly declares foo(_:y:)
> 
> This would also make `init` and `func` parameters behave consistently, which is nice. There may still be hope for our keyword argument rules to one day be shorter than the Smalltalk spec…

+1. (This was actually in my mental list of things to propose.)

I believe this leaves only subscripts with a rule that doesn't label all parameters. Subscripts (or at least unary subscripts) *should* usually have unlabeled parameters, but having a single rule might be worth requiring `_` in those.

I also think there's a good case for bringing back something like the old `#foo`, but that's a separable issue.

-- 
Brent Royal-Gordon
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