In support to blog post https://codewithshabib.com/2017/02/25/singletons-pattern-or-anti-pattern/

DependencyInjectionExample.swift

class User {
  var name = ""
  var age = 0
}

class EditUserInfoController {
  var user: User
  init (user: User) {
    self.user = user
  }
  
  func editUserName(_ username: String) {
    ...
  }
}

class GetFriendListController {
  let user: User
  init (user: User) {
    self.user = user
  }
  
  func getFriends () {
    ...
  }
}