How to set Swift version 5 (for recent dev snapshots) in Xcode build settings?

[Jens]

Well, here's the most recent example that I know of where the behavior is different between Swift 5 and 4.2 (at least in recent snapshots), repeated here for clarity:

func hmm(_ fn:  (Int, Int)  -> Int) { print("two ints") }
func hmm(_ fn: ((Int, Int)) -> Int) { print("pair") }

func test() {
  let twoIntsFn: (Int, Int) -> Int = { $0 + $1 }
  let pairFn: ((Int, Int)) -> Int =  { $0.0 + $0.1 }

  hmm(twoIntsFn) // error with both Swift 5 and Swift 4.2
  hmm(pairFn) // OK with Swift 5, error in Swift 4.2
}
test()

@Slava_Pestov

Note that hmm(pairFn) is ambiguous only with -swift-version 4, because we allow the splatting conversion in both directions. If I recall, this was due to an oversight in the old implementation.

In -swift-version 5, only one direction is allowed.

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All I was trying to say was that I'm a bit surprised at how uncommon an activity it seems to be to try out recent snapshots and switch between an upcoming Swift version and the current one, at least from within Xcode.