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From: Christoph Bauer <christoph.bauer@lms-gmbh.de>
To: caml-list <caml-list@inria.fr>
Subject: generic Hashtbl.to_array
Date: Tue, 25 Jul 2006 10:29:22 +0200
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Hi,

what is the best way to write Hashtbl.to_array?

Hashtbl.to_array : ('a, 'b) Hashtbl.t -> ('a * 'b) array

The simples idea has the problem, that you don't have
a initial value to make the result array:

let to_array t =
  let a =  Array.init make (Hashtbl.length t) ?init?  in
    ignore
      (Hashtbl.fold
         (fun k v i ->
            a.(i) <- (k, v); i + 1)
         t 0);
    a

The best solution I found is

let to_array t =
  let dummy =  Array.init 0 (fun _ -> raise Not_found) in
    fst
      (Hashtbl.fold
         (fun k v (a, i) ->
            if i = 0 then  
              let a = Array.make (Hashtbl.length t) (k, v) in
                (a, 0)
            else (a.(i) <- (k, v); (a, i + 1)))
         t (dummy, 0))

Is there a better one?

Thanks,
Christoph Bauer