クロージャ式でのタプルの分解、将来的にありえそう？↓ Core Team の John McCall 。

> Personally I agree that closures worth their own syntax and that it is important to keep closure's syntax lightweight. So, IMO we should keep {x, y in ..} syntax for closures and this should be jut equivalent for {(x, y) in ..}, i.e. one can use first or second depending on his/her style. > > I think the idea of double parentheses for tuple argument destructing in closure is the best solution as it has a relationship to introduced by SE-0066 type of function with tuple argument. I.e. : Yes, I agree. We need to add back tuple destructuring in closure parameter lists because this is a serious usability regression. If we're reluctant to just "do the right thing" to handle the ambiguity of (a,b), we should at least allow it via unambiguous syntax like ((a,b)). I do think that we should just "do the right thing", however, with my biggest concern being whether there's any reasonable way to achieve that in 4.0.

https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170522/036846.html