module Int_field = struct
  type t = { mutable x : int; }
  let create x = { x }
  let set t x = t.x <- x
end

module Poly_field = struct
  type 'a t = { mutable x : 'a; }
  let create x = { x }
  let set t x = t.x <- x

  let set_dynamic t x =
    let old_obj = Obj.repr t.x in
    let new_obj = Obj.repr x in
    if Obj.is_int old_obj && Obj.is_int new_obj then
      Array.unsafe_set (Obj.magic t : int array) 0 (Obj.magic x : int)
    else if not (old_obj == new_obj) then
      t.x <- x
  ;;
end

let () =
  let time_it desc f =
    let start = Sys.time () in
    f ();
    let elapsed = (Sys.time ()) -. start in
    Printf.printf "%s took %6f%!\n" desc elapsed;
  in

  let times = 200_000_000 in
  time_it "int field" (fun () ->
    let t = Int_field.create 0 in
    for i = 1 to times do
      Int_field.set t i;
    done);

  time_it "poly field" (fun () ->
    let t = Poly_field.create 0 in
    for i = 1 to times do
      Poly_field.set t i;
    done);

  time_it "poly field with dynamic check" (fun () ->
    let t = Poly_field.create 0 in
    for i = 1 to times do
      Poly_field.set_dynamic t i;
    done);
;;