How to create a shared part between two object - swift

Question

List and User are 2 classes. List contains title and a set of movies someone may likes. The class User has a AddList(_: List) method. It add new movie list to object of User type
class List {
var title : String = "General"
var movies = [String]()
init(title: String){
self.title = title
}
init(title: String, movies: [String]){
self.title = title
self.movies = movies
}
}
class User {
private let userID: Int
let userName: String
private var movieList = [String: [String]]() // the list is a Dictionaly, the value of the dictionalry is a string array
init(userID: Int, userName: String){
self.userID = userID
self.userName = userName
}
func AddList(newMovieList: List) -> Dictionary<String, [String]> {
self.movieList.updateValue(newMovieList.movies, forKey: newMovieList.title)
return self.movieList
}
}
3 movie list had beend inilizied as follow
var actionMovieJhon = List(title: "Action", movies: ["The Equalizer", "Mad Max: Fury Road", "Star Wars"])
var actionMovieAnna = List(title: "Action", movies: ["Batman v Superman: Dawn of Justice", "American Sniper", "The Martia"])
var shareMovie = List(title: "ShareAction", movies: ["MovieA", "MovieB", "MovieC"])
And then 2 User objdects Jhon and Anna with ther own movie list was created
var Jhon = User(userID: 1001, userName: "Jhon")
var Anna = User(userID: 1002, userName: "Anna")
Jhon.AddList(actionMovieJhon)
Anna.AddList(actionMovieAnna)
Question: How can I add the shared movie list (sharMovie) into the dictionalry of Jhon and Anna, so that anything changed in the shared list of Jhon will get updated in the side of Anna and vice versa.
In anther word, the "dictionary" of Jhon and Anna has their own part and shared part. But the shared part is referenced to the same list object
More Question: I had feelings that the method self.movieList.updateValue is not update by reference
Thanks a lot for your help

Answer 1

The code is based on the sorece code provided by "Swift Apprentice, Beginning programming with Swift 2.2", chapter 14: Classes
import Foundation
class List {
let name: String
var movies: [String] = []
init(name: String){
self.name = name
}
func printList() {
print("Movie List: \(name)")
for movie in movies{
print(movie)
}
print("\n")
}
}
class User {
var lists: [String: List] = [:]//****
func addList(list: List){
lists[list.name] = list
}
func listForName(name: String)-> List? {
print(lists[name]?.movies)
return lists[name]
}
}
//create user
let jane = User()
let john = User()
let people = User()
//create list
var johnActionMovie = List(name: "ActionJhon")
var janeActionMovie = List(name: "ActionJane")
var sharedMovie = List(name: "SharedMovie")
var publicIntrest = sharedMovie
//call addList(_:) method on user object
jane.addList(janeActionMovie)
john.addList(johnActionMovie)
jane.addList(sharedMovie)
john.addList(sharedMovie)
people.addList(publicIntrest)
//private part appending
jane.lists["ActionJane"]?.movies.append("janeA")
jane.lists["ActionJane"]?.movies.append("janeB")
jane.lists["ActionJane"]?.movies.append("janeC")
john.lists["ActionJhon"]?.movies.append("johnA")
john.lists["ActionJhon"]?.movies.append("johnB")
john.lists["ActionJhon"]?.movies.append("johnB")
//Shared part appending
john.lists["SharedMovie"]?.movies.append("shareA")
jane.lists["SharedMovie"]?.movies.append("shareB")
people.lists["SharedMovie"]?.movies.append("shareC")
//print out the result
john.listForName("ActionJhon")
john.listForName("SharedMovie")
jane.listForName("ActionJane")
jane.listForName("SharedMovie")
people.listForName("SharedMovie")
//further check
print(jane.lists["ShareMovie"] === people.lists["ShareMovie"])
print(jane.lists["ActionJane"] === john.lists["ActionList"])