weak_and_finalizers.ml

let w = Weak.create 2

let gen () =
  let x = "Hello" ^ string_of_int (Random.int 50) in
  Weak.set w 0 (Some x);
  let f () = () in
  Gc.finalise_last (fun () -> ignore (Sys.opaque_identity x)) f;
  f

let forgetful_gen2 () =
  let x = "world"  ^ string_of_int (Random.int 50) in
  Weak.set w 1 (Some x);
  let f () = () in
  f

let () =
  let f = gen () in
  let g = forgetful_gen2 () in
  Gc.compact ();
  begin match Weak.get w 0 with
  | None -> Format.printf "Forgotten@."; assert false
  | Some x -> Format.printf "Remembered %s@." x
  end;
  begin match Weak.get w 1 with
  | None -> Format.printf "Forgotten@."
  | Some x -> Format.printf "Remembered %s@." x; assert false
  end;
  f (); g ()