module Registry(Obj : sig

    type t = private < .. >

  end) : sig

  val register_obj : string -> Obj.t -> unit

  val get_obj : string -> Obj.t

end

module Registry(Obj : sig

    type t = private < .. >

  end) = struct

  let objs = ref []

  let register_obj name obj = objs := (name, obj) :: !objs

  let get_obj name = List.assoc name !objs

end

class foo = object

  method hello = "hello from foo"

  method goodbye () = print_endline "goodbye"

end

class bar = object

  method hello = "hello from bar"

end

module Bars = List_fns.Registry(struct type t = bar end)

let () =

  let o1 = new foo in

  let o2 = new bar in

  Bars.register_obj "o1" (o1 :> bar);

  Bars.register_obj "o2" (o2 );

  print_endline ("calling o1: " ^ (Bars.get_obj "o1")#hello);

  print_endline ("calling o2: " ^ (Bars.get_obj "o2")#hello)