A few confusing points on the recap code challenge

Jane (1) Yes, the point of initializers are to make sure all member variables are initialized. So if they take values for those variables as parameters in the initializer, those values need to be assigned to the appropriate member variables. There are two basic ways to do this. One uses self:

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

Here values for x and y are passed in, and assigned to member variables named x and y. self is used to disambiguate the member variable from the local variable. Some programers don't really like self (or this in other languages like Java) so they give the formal parameters different names instead:

    init(ax: Int, ay: Int){
        x = ax
        y = ay
    }

Since there's no ambiguity between the member variable x and the local variable ax self isn't needed.

(2) Think of self as a possessive pronoun: my. E.g., my x, my y You can use it anywhere you reference a member variable (in the same class). You don't need self in self.location.x, because there's no ambiguity. But it doesn't hurt if you add it. What you would be saying is "member x of my location Point variable". Here's a version (with if...else... rather than switch) without self and it works fine:

class Robot: Machine {

  override func move(direction: String) {
    if direction == "Up" {
      location.y++
    } else if direction == "Down" {
      location.y--
    } else if direction == "Left" {
      location.x--
    } else if direction == "Right" {
      location.x++
    }
  }
}

But this version with self works just as well:

class Robot: Machine {

  override func move(direction: String) {
    if direction == "Up" {
      self.location.y++
    } else if direction == "Down" {
      self.location.y--
    } else if direction == "Left" {
      self.location.x--
    } else if direction == "Right" {
      self.location.x++
    }
  }
}

I've seen books (for Java programming languages) that say explicitly that using this.x is very bad practice, and I've seen others that say it's the preferred or best practice! If I remember correctly I think the Apple documentation weighs in for self on the yes, use it side. Hope this helps.