message: It is now an error to access String.characters in Swift 5 mode.
diff: @@ -57,7 +57,7 @@ class A
  {
  get
  {
  - return input.characters.count // In string subscript getter
  + return input.count // In string subscript getter
  }
  set (new_value)
  @@ -75,7 +75,7 @@ class A
  init (_ input: String)
  {
  - in_class_a = input.characters.count
  + in_class_a = input.count
  also_in_a = in_class_a + 1
  print ("In string init.")
  }
  