cast.ml

class cs = object
  method kuwa = prerr_endline "kuwa"
end

class ca = object
  inherit cs
  method x = 1
end

class cb = object
  inherit cs
  method y = 2
end

let call a f =
  let tag = CamlinternalOO.public_method_label f in
  let methods = Obj.magic (Obj.field (Obj.magic a) 0) in
  let len = Obj.magic methods.(0) in
  let rec loop i =
    if i = len then raise Not_found
    else if methods.(i*2+3) = Obj.magic tag then Obj.magic (CamlinternalOO.send (Obj.magic a) tag)
    else loop (i + 1)
  in
  try Some (loop 0)
  with Not_found -> None

let () =
  let a = new ca in
  let b = new cb in
  let ss = [ (a :> cs); (b :> cs) ] in
  List.iter (fun s -> s#kuwa) ss;
  let a':ca = Obj.magic (List.nth ss 0) in
  let b':cb = Obj.magic (List.nth ss 1) in
  Printf.printf "%d\n" a'#x;
  Printf.printf "%d\n" b'#y;
  List.iter (fun s ->
    match (call s "x") with
    | Some n -> Printf.printf "Some(%d)\n" n
    | None -> Printf.printf "None\n")
    ss