Swift 1.2 - Error caused by closure parameters of a class function

Question

Since I upgraded to Swift 1.2, I have this weird problem, that I cannot resolve. Here is the code that causes all the trouble:

internal class Test<T,U> {
    internal class func closureFunc(#arg: T, worker: (first: T, second: String) -> U, closure: ((u: U) -> Void)?) -> Void {
        println("Something")
    }
}
Test.closureFunc(arg: "", worker: { (first, second) -> Void in
    //code
    }) { (u) -> Void in
    //code
}

The error itself says:

"Function signature (Void) -> Void is not compatible with expected type (u: Void) -> Void".

I read all about Swift 1.2 and I still can't seem to find a reasonable explanation for this. I will be extremely thankful for any tips and suggestions.

PS: I just saw this topic, that is similar to mine but removing the parameter name in the closure didn't quite work for me.

Qbyte · Accepted Answer · 2015-07-15 16:34:42Z

1

This seems to be a bug in Swift 1.2 (and even Swift 2 (Xcode 7 beta 3)) with single parameter closures with external names.

As workaround you can remove the external parameter name "u":

internal class func closureFunc(#arg: T, worker: (first: T, second: String) -> U, closure: (U -> Void)?) -> Void

in Swift 2 (only) there is another workaround where you can give the passed closure an external name (since this would conform to the new and more strict naming conventions):

Test.closureFunc(arg: "", worker: { (first, second) -> Void in
    //code
    }) { (anyExternalNameWorks u: Void) -> Void in
    //code
}

answered Jul 15, 2015 at 16:34

Qbyte

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