title: Managing GameScenes update method and referencing changing instance properties within other classes
body: <p>I'm making my first game in Swift and I'm trying to get a <code>SKSpriteNode</code> subclass instance (<code>trailingSprite</code>) to follow or "trail" another <code>SKSpriteNode</code> subclass (<code>User</code>) that the user controls. I was able to achieve this by making a <code>move(aUser:User)</code> method within the <code>trailingSprite</code> class that applies a velocity vector to to the trailing body thats the difference of the two <code>postions</code> I then call this method inside of GameScenes <code>Update</code> function. However, this <code>trailingSprite</code> isn't always on screen and can spawn at random times in differing quantities. Is there a more effective way of retrieving "live" or updated positions of the <code>User</code> instance within each <code>trailingSprite</code> instance instead of having to call a move method for each one inside of Update (which ultimately wont work)? I also tried passing the <code>User</code> instance by reference but this still didn't work as the velocity vector never updated from the original positions. Any help would be awesome!</p>