xcode - Arrays and Swift

Question

I'm trying to deal with an app in Swift and I'm facing the following error using arrays:

fatal error: Array index out of range

This appears when apps assign a value to the array at index 0:

class DrawScene: SKScene {

    init(size: CGSize) {
        super.init(size: size)
    }

    var line = SKShapeNode()
    var path = CGPathCreateMutable()
    var touch: UITouch!
    var pts = [CGPoint]()

    override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
        /* Called when a touch begins */
        touch = touches.anyObject() as UITouch!
        self.pts[0] = touch.locationInNode(self)  <-- Error appears here
        drawLine()
    }

Some ideas? (I'm using xcode 6 Beta 4)

Answer 1

Your array is empty at first.

if self.pts.isEmpty {
    self.pts.append(touch.locationInNode(self))
}
else {
    self.pts[0] = touch.locationInNode(self)
}