PackageKVO.swift

final class Package: NSObject {
  @objc dynamic var recipient = Person()
  @objc dynamic var sender = Person()
  @objc dynamic var contents = [PackageContent]()
}

final class Person: NSObject {
  @objc dynamic var firstName: String = ""
  @objc dynamic var lastName: String = ""
  @objc dynamic var postalAddress = CNPostalAddress()
}

final class PackageContent: NSObject {
  init(title: String, weight: Int) {
    self.title = title
    self.weight = weight
  }
    
  let title: String
  let weight: Int
}