Oh, I completely forgot that it’s only $n you have to reference, not $n-1 or anything else. So I guess it’s not quite serving the purpose I thought it was.
Jordan
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On May 20, 2016, at 10:25, John McCall <rjmccall@apple.com> wrote:
On May 19, 2016, at 4:13 PM, Jordan Rose via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
On May 14, 2016, at 22:16, Chris Lattner via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
On May 13, 2016, at 9:16 AM, Joe Groff via swift-evolution <swift-evolution@swift.org <mailto: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.
Sorry to find this thread late. I don’t think this is just a bug; it’s also a way to check that a parameter isn’t getting forgotten. For a single-expression closure that’s probably overkill, but maybe we’d keep the restriction for multi-statement closures?
The bug we're talking about is that closures have to have a reference to $n when there are n+1 parameters.