instance method

enum Traffic {
  case light
  case heavy
  mutating func reportAccident() {
    self = .heavy
  }
}
var currentTraffic: Traffic = .light
currentTraffic. reportAccident()
// currentTraffic is now .heavy

Just like classes and structs, enumerations can have instance methods. If an instance method mutates the value of the enum, it needs to be marked mutating