Pass Computed Values as Parameters in Swift - ios

Question

I am making a custom animation handler class with swift, and GameKit. In summary, I want to initialize an Animator (a custom class), on any SKNode that I want to animate. In principle, this animator has a list of animations (SKActions) that all have various "trigger States", which correspond with the various game states the game can be in. The Animator class then observers the global state variable, and if it changes, and matches the animations' trigger states, then it runs that animation on the target node.
I got this to work, however, I want to add just a bit more functionality to this, in the form of changing timings for the animation. An example of this would be something like a dog running, perhaps over a set period of time (where the state does not change), I want the dog to start running fast, and slow over time. The way I'm thinking of implementing something like this is to have a variable, speed, for example, that represents the speed of the animation, and have it slow over time. Then I would pass in a computed property (return the current value of the speed var)to the animator class, such that every time it calls the function for this specific animation, instead of having a fixed time interval, it would get the speed var and pass it in.
I'm having trouble because when I pass in a computed property, swift just takes its value when it's getting passed and holds onto that, instead of taking the entire getter with it. I'm wondering if there is a way I can pass a computed property with a getter, into a function/class. Here is the animator classes that I'm referring to, if you would like to see some code :)
class Animation {
let waitForCompletion: Bool
let repeating: Bool
let animation: SKAction
var running: Bool = false
let triggerState: State
var currentState: State {
return States.currentState
}
let target: SKNode
init(_ triggerState: State, animates animation: SKAction, for target: SKNode, waitForCompletion: Bool = true, repeating: Bool = true) {
self.triggerState = triggerState
self.target = target
//here I simply just pass in an animation, which allows for grouping animations if I want to do more than jsut SKAction.Animat(with:,timeInterval:)
self.waitForCompletion = waitForCompletion
self.repeating = repeating
self.animation = animation
}
func update(_ first: Bool) {
if (currentState == triggerState || first) && !running {
self.running = true
if !self.waitForCompletion { target.removeAllActions() }
if !target.hasActions() {
target.run(animation) {
self.running = false
self.target.removeAllActions()
if self.repeating { self.update(false) }
}
}
}
}
}
heres the animator class:
class Animator {
var itemObserver: AnyCancellable?
var animations: [Animation] = []
var state: State {
didSet {
update()
}
}
init(_ animations: [Animation]) {
self.animations = animations
self.state = States.currentState
//initialize a temporary value, such that the class has initialized self
itemObserver = States.$currentState.sink() { let _ = ($0) }
itemObserver = States.$currentState
.sink() { self.state = $0 }
}
func update() {
if let animation = animations.first(where: {$0.triggerState == state}) {
animation.update(true)
}
}
}
and a sample initialization in an SKNode class:
//this initializes the animtor with a series of animations. The animation being passed here is a group animation(an important capabality of this system, and in the scaleY, I pass a stretchVar, which is a computed property, that only passes its value in this example)
animator = Animator([
Animation(State.throwing, animates: SKAction.group([
SKAction.animate(with: ballAtlas, timePerFrame: 0.1),
SKAction.scaleY(to: stretchVar, duration: 0)
]), for: self)
])