struct Tutorial {
      var difficulty: Int = 1
  }
  var tutorial1 = Tutorial()
  var tutorial2 = tutorial1
  tutorial2.difficulty = 2
  print(tutorial1.difficulty) //1
  print(tutorial2.difficulty) // 2
  class Manual {
    var difficult:Int = 1
  }
  var manual1 = Manual()
  var manual2 = manual1
  manual2.difficult = 2
  print(manual1.difficult) //2
  print(manual2.difficult) //2