[swift-evolution] [swift-evolution-announce] [Review] SE-0111: Remove type system significance of function argument labels

Michael Ilseman milseman at apple.com
Thu Jun 30 17:33:54 CDT 2016

> On Jun 30, 2016, at 11:43 AM, Scott James Remnant via swift-evolution <swift-evolution at swift.org> wrote:
> -1
> This proposal doesn’t even use Swift naming style to make its point, as soon as you do, the reason why Swift considers argument labels to be part of the type signature becomes apparent. 
> The author of the proposal uses the following example:
>  func doSomething(x: Int, y: Int) -> Bool
> This is just not Swift-y, a much better example would be:
>  func sinkBattleship(atX x: Int, y: Int) -> Bool

If you want to talk about pedantic following of API naming guidelines for example code, then I believe that your example also runs afoul. It would be:

func sinkBattleshipAt(x: Int, y: Int) -> Bool

Due to a special case where the preposition covers multiple arguments. This arrises mostly from flatten-ed structs as parameters, e.g. from old C APIs predating struct literal syntax. See:

An exception arises when the first two arguments represent parts of a single abstraction.

a.move(toX: b, y: c)
a.fade(fromRed: b, green: c, blue: d)
In such cases, begin the argument label after the preposition, to keep the abstraction clear.

a.moveTo(x: b, y: c)
a.fadeFrom(red: b, green: c, blue: d)


> the proposal states that the argument labels be then stripped from the type, which would make this method type-compatible with:
>  func meetsBattingAverage(ofHits hits: Int, forRuns runs: Int) -> Bool
> I don’t think it’s desirable for this to work at all… Argument labels are not parameter names, they are a first class part of Swift’s type system, and always meaningful when employed properly.
> Scott
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