OCaml 4.03: Everything else(blogs.janestreet.com)

    lolcathost% ocaml
            OCaml version 4.02.3
    
    # class foo =
        object (_ : 'a)
          method test (_ : 'a) = ()
        end;;
    class foo : object ('a) method test : 'a -> unit end
    # class bar =
        object
          inherit foo
          method other = ()
        end;;
    class bar : object ('a) method other : unit method test : 'a -> unit end
    # let f = new foo;;
    val f : foo = <obj>
    # let b = new bar;;
    val b : bar = <obj>
    # f#test f;;
    - : unit = ()
    # b#test b;;
    - : unit = ()
    # f#test b;;
    Characters 7-8:
      f#test b;;
             ^
    Error: This expression has type bar but an expression was expected of type
             foo
           The second object type has no method other
    # b#test f;;
    Characters 7-8:
      b#test f;;
             ^
    Error: This expression has type foo but an expression was expected of type
             bar
           The first object type has no method other
    #