Hands-On Design Patterns with Swift

Adding methods

Now, we may want to add a method to this State enumeration. After all, it's very common to just toggle the switch on and off without thinking:

extension State {    mutating func toggle() {        self = self == .off ? .on : .off    }}var state: State = .onstate.toggle()state == .off // true

As in the previous section, we can just extend the State enum to add the toggle functionality. Enums follow value semantics; therefore, we have to mark the toggle method as mutating.