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iOS Swift 2.0 Enumerations and Optionals Introduction to Enumerations Enums and Objects

Paul Je
Paul Je
4,435 Points
Posted by Paul Je
Paul Je
4,435 Points

Looking for Explanation

Hey guys,

Just kind of confused and wanted to clarify. Does "switch" mean you're switching the constraint (direction) for the result of each case? If not, what's an easy description on how to understand what a switch is?

Secondly, what's the reasoning behind using location.y instead of Point.y for example?

classes.swift 
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 Robot {
    var location: Point

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

    func move(direction: Direction) {
        // Enter your code below
        switch direction {
        case .Left: location.x -= 1
         case .Right: location.x += 1
          case .Up: location.y += 1 
           case .Down: location.y -= 1

    }
}

3 Answers

jcorum
jcorum
71,830 Points

Paul, just noticed you have a missing closing curly brace:

    func move(direction: Direction) {
        // Enter your code below
        switch direction {
        case .Left: location.x -= 1
         case .Right: location.x += 1
          case .Up: location.y += 1 
           case .Down: location.y -= 1
        }  //missing
    }

The function takes one parameter, a direction. Think of switch as a shorthand way of writing if...else if...else... statements. Thinking this way, the first case says: if direction is Left, then do something. The second case says: else if direction is Right, then do something different.

In each case, what is done is either the x or y value of location (which is a Point) is incremented or decremented.

Damien Watson
Damien Watson
27,419 Points
Damien Watson
Damien Watson
27,419 Points

Hi Paul,

A 'switch' statement checks a variable and then directs the flow to the relevant code. As in real life, when a train arrives at a switch based upon what train it is, it is then directed to the relevant track (I know nothing of trains so forgive my ignorance train lovers ;).

Another way to think of a switch (thought much messier) is using if statements, else if, else if etc.

Location is created as a variable of method Point, so using Point.y wouldn't make sense. When you set Location = Point(x:0, y:0), you are saying set Location to a Point object with x=0 and y=0.

Paul Je
Paul Je
4,435 Points
Paul Je
Paul Je
4,435 Points

Thanks guys makes so much more sense !