Note.swift

final class Note {
    init(topic: String, text: String) {
        self.topic = topic
        self.text = text
    }
    
    var topic: String = "" {
        didSet {
            print("Topic changed to \(topic).")
        }
    }
    
    var text: String = "" {
        didSet {
            print("Text changed to \(text).")
        }
    }
}