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

Scott James Remnant scott at netsplit.com
Thu Jun 30 19:02:38 CDT 2016

> Is there an example of two functions, obeying the naming guidelines, which have different argument labels (not parameter names) for parameters of the same type, where it makes sense to cross-call them?
> Sure there are. For example, `adding(_:)` and `multiplied(by:)` in the new Integer protocol.

These have quite different results!

I’m pretty convinced that Swift shouldn’t implicitly allow you to assign multiplied(by:) to the same member as you could assign adding(_:) - explicit is fine, with some syntax e.g. through a closure, but not implicit!

To correct my goofy pre-coffee not-quite-following-the-naming-guidelines suggestion, that would be equivalent of allowing these two to be interchangeable:

  func drawLineTo(x: Float, y: Float)
  func drawLineWith(angle: Float, distance: Float)

Which is clearly not something you would expect to be allowed implicitly.

I’m definitely for the concept of the proposal that this is inconsistent, but I’m also definitely for making this explicitly disallowed everywhere, not allowed everywhere.

I think Erica makes a good point about syntax too, we’ve been assuming:

  // compatible types
  var x = drawLineTo
  x = drawLineWith

but really this isn’t Swifty syntax, the full argument labels provide more clarity here; and I’d even be in favor of disallowing the above shortening.


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