From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id LAA09095; Thu, 17 Jan 2002 11:57:44 +0100 (MET)
X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id LAA09400 for <caml-list@pauillac.inria.fr>; Thu, 17 Jan 2002 11:57:44 +0100 (MET)
Received: from verdot.inria.fr (verdot.inria.fr [128.93.11.7])
	by concorde.inria.fr (8.11.1/8.11.1) with ESMTP id g0HAvhX00546
	for <caml-list@inria.fr>; Thu, 17 Jan 2002 11:57:43 +0100 (MET)
Received: (from ddr@localhost)
	by verdot.inria.fr (8.9.3/8.9.3) id LAA24240
	for caml-list@inria.fr; Thu, 17 Jan 2002 11:57:43 +0100
Date: Thu, 17 Jan 2002 11:57:43 +0100
From: Daniel de Rauglaudre <daniel.de_rauglaudre@inria.fr>
To: caml-list@inria.fr
Subject: Re: [Caml-list] Type hidding
Message-ID: <20020117115743.G23800@verdot.inria.fr>
References: <001601c19ec9$bfe251e0$eb00a8c0@warp>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.2.5i
In-Reply-To: <001601c19ec9$bfe251e0$eb00a8c0@warp>; from warplayer@free.fr on Wed, Jan 16, 2002 at 09:09:48PM +0100
Sender: owner-caml-list@pauillac.inria.fr
Precedence: bulk

Hi,

On Wed, Jan 16, 2002 at 09:09:48PM +0100, Warp wrote:

> external set_window_data : wnd:hwnd -> 'a -> unit = "set_window_data"
> external get_window_data : wnd:hwnd -> 'a = "get_window_data"
> 
> I know that's very type-unsafe and all, but i really need the user to be
> able to put any kind of data into it. If you got another idea, please let me
> know.

If you don't want to give type parameters to hwnd, like suggested, and
if the stored values are monomorphic, you can use this system of
monomorphic dynamics.

The following function creates a system of dynamics, which are values
of type unit -> unit. It returns a couple a two functions, one to
convert any monomorphic type into a dynamic, the other returning a
value from its corresponding dynamic:

   let make_dyn () =
     let r = ref None in
     let set x () = r := Some x in
     let get d =
       r := None;
       d ();
       match !r with
	 Some x -> x
       | None -> failwith "bad type"
     in
     set, get

Example:

   let set_int, get_int = make_dyn ()
   let set_string, get_string = make_dyn ()
   
   let x = set_int 32
   let y = set_string "abc"
   let z = set_int 8

   get_int x
   -> 32
   get_int z
   -> 8
   get_string y
   -> "abc"
   get_int y
   -> failed "bad type"

-- 
Daniel de RAUGLAUDRE
daniel.de_rauglaudre@inria.fr
http://cristal.inria.fr/~ddr/
-------------------
Bug reports: http://caml.inria.fr/bin/caml-bugs  FAQ: http://caml.inria.fr/FAQ/
To unsubscribe, mail caml-list-request@inria.fr  Archives: http://caml.inria.fr