[swift-evolution] Revisiting SE-0110

[John McCall]

> On May 25, 2017, at 2:23 PM, Nevin Brackett-Rozinsky via swift-evolution <swift-evolution at swift.org> wrote:
> One possibility is to make parentheses consistently meaningful in closure argument lists, so that “(a, b)” would exclusively mean “there is one parameter of tuple-type, which is being destructured”, while “a, b” without parentheses would exclusively mean “there are two parameters”.
> 
> That way you can destructure a tuple parameter if you wish (by using parentheses) or you can leave the tuple intact (by listing a single identifier without parentheses).

The problem with this is that we also need some way to be explicit about the return type, and it would be strange to allow (and require!)
  { a, b -> Int in }
when that's not at all a valid way to write a function type.  Also it would be an enormous source break, even worse than this problem.

That said, I'm quite sympathetic to the idea that directly destructuring tuples in closure parameter lists is too useful to lose, even if it's ambiguous.

John.