Enum Methods, Swift 3

Not sure what I'm doing wrong, pointers would be appreciated.

'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.'

Also, might be an error with the checker. It asks to make a constant with the name button, but the error code asks me to make sure it's called doneButton?

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

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

func button() -> UIBarButtonItem {
        switch self {
        case.done(nil): return UIBarButtonItem(title:"done")
        case.edit(nil): return UIBarButtonItem(title:"plain")
        }
    }
}

let done = BarButton.done(title:"Save")
let doneButton = UIBarButtonItem(title: "A Title", style: .plain, target: nil, action: nil)