Increasing/Decreasing waitForDuration( )? - swift

Question

I am wondering if its possible to increase withForDuration( ) with a variable. Heres how I am trying to do it in short. This is also SpriteKit, and this is my first time with it so I am still a little unsure. While this snippet of code works to change the float it doesn't actually change the waitForDuration(difficulty)
var timer: NSTimer!
var difficulty = 1.0
override func didMoveToView(view: SKView) {
backgroundColor = SKColor.whiteColor()
player.position = CGPoint(x: size.width * 0.5, y: size.height * 0.25)
player.physicsBody = SKPhysicsBody(circleOfRadius: player.size.width/2)
player.physicsBody?.dynamic = true
addChild(player)
physicsWorld.gravity = CGVectorMake(0, 0)
physicsWorld.contactDelegate = self
var timer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: "increaseDifficulty", userInfo: nil, repeats: true)
runAction(SKAction.repeatActionForever(
SKAction.sequence([
SKAction.runBlock(addEnemy),
SKAction.waitForDuration(difficulty)
])
))
}
func increaseDifficulty() {
difficulty -= 0.1
}

Answer 1

One way to do this is to use the completionHandler of the runAction function. For example.
func addEnemyWithChangingDifficulty() {
let waitAction = SKAction.waitForDuration(difficulty)
let addEnemyAction = SKAction.runBlock { () -> Void in
self.addEnemy()
}
runAction(SKAction.sequence([addEnemyAction,waitAction]), completion: { () -> Void in
self.addEnemyWithChangingDifficulty()
})
}
Another way would be to use the update function to track the waitDuration.
var lastAddedTime : CFTimeInterval = 0
override func update(currentTime: CFTimeInterval) {
if currentTime - lastAddedTime > CFTimeInterval(difficulty) {
addEnemy()
lastAddedTime = currentTime
}
}

Answer 2

You're not getting your intended effect because the value of 'difficulty' is captured in the first declaration of your SKAction and it never refers to the outside declaration again.
Two ways to solve this:
Instead of doing SKAction.repeatActionForever(), dump the SKAction.sequence() in increaseDifficulty. You'll have to tweak the numbers a bit to make it work, but NSTimer is already running on repeat, you can use that instead.
The second way (not 100% sure about this) is to put the '&' symbol in front of difficulty. This passes difficulty by reference rather by value, which should give you the intended effect. I'm just not sure if Swift allows this, but in C++ that's what we can do.