Yeah, this is just a bug which several people have made various efforts over the last three years to fix. It's not easy.
John.
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On May 14, 2016, at 10:16 PM, Chris Lattner via swift-evolution <swift-evolution@swift.org> wrote:
On May 13, 2016, at 9:16 AM, Joe Groff via swift-evolution <swift-evolution@swift.org> wrote:This encourages the use of empty closures over optional closures, which I think is open for debate. In general I try to avoid optionals when they can be precisely replaced with a non-optional value. Furthermore, most Cocoa completion handlers are not optional.
The alternative is to not do this, but encourage that any closure that could reasonably be empty should in fact be optional. I would then want Cocoa functions with void-returning closures to be imported as optionals to avoid "{ _ in }".
+1. In general, I think we should allow implicit arguments, without requiring the closure to use all the implicit $n variables like we do today. These should all be valid:
let _: () -> () = {}
let _: (Int) -> () = {}
let _: (Int, Int) -> Int = { 5 }
let _: (Int, Int) -> Int = { $0 }
let _: (Int, Int) -> Int = { $1 }I agree, but I consider this to be an obvious bug in the compiler. I don’t think it requires a proposal.
Unfortunately it is non-trivial to fix…