(*
copyright (c) 2013-2014, simon cruanes
all rights reserved.

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(** {1 Hash Table with Heterogeneous Keys} *)

type 'a t = ('a, (unit -> unit)) Hashtbl.t

type ('a, 'b) injection = {
  getter : 'a t -> 'a -> 'b option;
  setter : 'a t -> 'a -> 'b -> unit;
}

let create n = Hashtbl.create n

let access () =
  let r = ref None in
  let getter tbl k =
    r := None; (* reset state in case last operation was not a get *)
    try
      (Hashtbl.find tbl k) ();
      let result = !r in
      r := None; (* clean up here in order to avoid memory leak *)
      result
    with Not_found -> None
  in
  let setter tbl k v =
    let v_opt = Some v in
    Hashtbl.replace tbl k (fun () -> r := v_opt)
  in
  { getter; setter; }

let get ~inj tbl x = inj.getter tbl x

let set ~inj tbl x y = inj.setter tbl x y

let length tbl = Hashtbl.length tbl

let clear tbl = Hashtbl.clear tbl

let remove tbl x = Hashtbl.remove tbl x

let copy tbl = Hashtbl.copy tbl

let mem ~inj tbl x =
  match inj.getter tbl x with
  | None -> false
  | Some _ -> true

let find ~inj tbl x =
  match inj.getter tbl x with
  | None -> raise Not_found
  | Some y -> y

let iter_keys tbl f =
  Hashtbl.iter (fun x _ -> f x) tbl

let fold_keys tbl acc f =
  Hashtbl.fold (fun x _ acc -> f acc x) tbl acc

let keys tbl =
  Hashtbl.fold (fun x _ acc -> x :: acc) tbl []

let bindings ~inj tbl =
  fold_keys tbl []
    (fun acc k ->
      match inj.getter tbl k with
      | None -> acc
      | Some v -> (k, v) :: acc)