Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

iOS Build a Simple iPhone App with Swift Getting Started with iOS Development Swift Recap Part 2

Please help!

Why is this not working? I've been stuck for over an hour.

class Point {
    var x: Int
    var y: Int

    init(x: Int, y: Int){
        self.x = x
        self.y = y

enum Direction {
    case Left
    case Right
    case Up
    case Down

class Machine {
   var location: Point

   init() {
            self.location = Point(x: 0, y: 0)

   func move(direction: String) {
            print("Do nothing! Im a machine!")

  class Robot: Machine {
            override func move(direction: String){
                switch direction {
                case "Up": location.y += 1
                case "Down": location.y -= 1
                case "Left": location.x -= 1
                case "Right": location.x += 1
                default: "dont move"

1 Answer

Christian Mangeng
Christian Mangeng
15,969 Points

Hi Carina,

this is a good example of how picky programming can be. If you restart the challenge you can see that the superclass "move" method explicitly has no external parameter name defined (see the underscore, you seem to have removed it). When you override this method later, it needs to override EXACTLY that kind of method, otherwise override will throw an error because you would override a new kind of method. Add this underscore in both the superclass and the overridden subclass method and you will pass:

   func move(_ direction: String) {