What's wrong in this code ?

QUESTİON Next, add a method to the enum named button that returns an instance of the class UIBarButtonItem configured properly. An example of how to create an instance for this task is shown in the comments below. Use the same initializer.

In the method, using the associated values as titles for the button, return a button with style UIBarButtonStyle.done for the done member of the BarButton enum. Similarly for the edit member, return a UIBarButtonItem instance with the style set to UIBarButtonStyle.plain.

In both cases you can pass nil for target and action. Once you have a method, call it on the value we created in the previous task and assign it to a constant named button.

// Example of UIBarButtonItem instance // let someButton = UIBarButtonItem(title: "A Title", style: .plain, target: nil, action: nil)

MY ANSWER

enum BarButton { case done(title: String) case edit(title: String)

func button() -> UIBarButtonItem {
    switch self {
    case .done(let title):
        return UIBarButtonItem(title: title, style: .done, target: nil, action: nil)
    case .edit(let title):
        return UIBarButtonItem(title: title, style: .plain, target: nil, action: nil)
    }
}

}

let done = BarButton.done(title: "Save") let button = BarButton.button(done)

EXCEPTİON Bummer! Your code could not be compiled. Please click on "Preview" to view the compiler errors.

However, "Preview" don't show any error to me.