2021-10-19 Constrained extension must be declared on the unspecialized generic type

Did you get the following error message in Swift?

    Constrained extension must be declared on the unspecialized generic type 'Optional' with constraints specified by a 'where' clause

I got that one, and I tried to extend an optional string as follows:

    extension Optional<String> {
        func ifEmpty(_ replacementString: String) -> String? {
            (self ?? "").isEmpty ? replacementString : self
        }
    }

The correct syntax is:

    extension Optional where Wrapped == String {
        func ifEmpty(_ replacementString: String) -> String? {
            (self ?? "").isEmpty ? replacementString : self
        }
    }

It's still painful that it must return an optional. That can be avoided by a static function, which isn't as nice of course :)