Swift - Why is Class Instance Appended to Array Deinitialized? - arrays

Question

I'm having memory problems with the Swift code below.
In GameScene's sceneDidLoad(), I add a GKEntity to the array "entities," but in GameScene's update(), the array "entities" is empty. Shouldn't the reference to "entity" be preserved in "entities"? Why is "entity" being deinitialized at the end of sceneDidLoad()?
import GameplayKit
class GraphicsComponent: GKComponent {
override func update(deltaTime: TimeInterval) {
// ...
}
}
class GameScene: SKScene {
var entities = [GKEntity]()
override func sceneDidLoad() {
let entity = GKEntity()
entity.addComponent(GraphicsComponent())
entities.append(entity)
}
override func update(_ currentTime: TimeInterval) {
// ...
for entity in entities {
entity.update(deltaTime: dt)
}
}
}
I was expecting the "entity" instance to be preserved because a reference to it was added to the "entities" array. If that reference remained, then why was the instance destroyed?
EDIT:
I found that if I move the code in sceneDidLoad() to didMove(), everything works as expected. I still didn't know why, so I looked around in the boilerplate that Xcode puts in GameViewController and found where sceneDidLoad() and didMove() are each called. I found that if I add an entity to the scene.entities array in sceneDidLoad(), the scene.entities array will be empty when the code steps into the if statement that begins with if let scene = GKScene(fileNamed: "GameScene"). Is the if let creating a temporary GKScene?
class GameViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// This "if let" will call sceneDidLoad(), which appends a new entity to scene.entities.
if let scene = GKScene(fileNamed: "GameScene") {
// scene.entities.count = 0
if let sceneNode = scene.rootNode as! GameScene? {
sceneNode.entities = scene.entities
sceneNode.graphs = scene.graphs
sceneNode.scaleMode = .aspectFill
if let view = self.view as! SKView? {
view.presentScene(sceneNode) // This calls didMove()
view.ignoresSiblingOrder = true
view.showsFPS = true
view.showsNodeCount = true
}
}
}
}
}