[swift-users] Compiler can't infer map transfer closure return type?

[Dennis Weissmann]

Hi Neil,

indeed the compiler should be able to infer the type here.

The error message in the latest development snapshot (swift-DEVELOPMENT-SNAPSHOT-2016-03-01-a) is a little better:

> Expression type '[_]' is ambiguous without more context


You can work around like this:

let x2 = [1,2].map { _ -> String in
  let x = "abc"
  return x
}

or

let x2: [String] = [1,2].map { _ in
  let x = "abc"
  return x
}

- Dennis

> On Mar 7, 2016, at 12:55 AM, Neil Faiman via swift-users <swift-users at swift.org> wrote:
> 
> Using the version of Swift in Xcode 7.2.1, I compile the following program:
> 
>    let x1 = [1,2].map { _ in
>        return "abc"
>    }
> 
>    let x2 = [1,2].map { _ in
>        let x = "abc"
>        return x
>    }
> 
> The assignment to x1 compiles successfully, but the assignment to x2 produces this error:
> 
>    Cannot invoke 'map' with an argument list of type '(@noescape (Int) throws -> _)'
>    Expected an argument list of type '(@noescape (Self.Generator.Element) throws -> T)'
> 
> It seems that in both calls, the transform closure is returning a String, so I don’t see why the compiler can infer the return type in one case, but not in the other. Am I missing something obvious?
> 
> Thanks,
> 
> 	Neil Faiman
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users

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