How to convert an APNs token to `String` from `Data`?

let token = deviceToken.map { String(format: "%.2hhx", $0) }.joined()

// Define initializer
extension String {
    public init(deviceToken: Data) {
        self = deviceToken.map { String(format: "%.2hhx", $0) }.joined()
    }
}

func application(_ application: UIApplication,
                 didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data!) {
    // Use like this:
    let token = String(deviceToken: deviceToken)
}