Why can't Swift closure variable types be implicitly unwrapped optionals?

Question

For example,

alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler:{ (x:UIAlertAction) in
...

will give a "Cannot find initializer with..." error.

But if I say UIAlertAction! or UIAlertAction? instead of just UIAlertAction , it works. Why is this?

Answer 1

The types of these variables are all declared already in the Cocoa API. You must match them. A thing and an Optional wrapping that thing are not a match; they are two completely different types.

On the other hand, when types are known you can just omit them. So the easiest thing is for you to change x:UIAlertAction to simple x or even _ .