@melrain Thanks very much for your question! I found the following potential solution to your problem:
You need to make GameScene conform to SKPhysicsContactDelegate, like so:
class GameScene: SKScene, SKPhysicsContactDelegate {
// …
}
Now you can implement the delegate methods you want, all the methods in SKPhysicsContactDelegate are optional, and they’ll get called at the appropriate time.
For more information on Protocols, I would recommend looking at The Swift Programming Language: Protocols