From: Olivier Andrieu <andrieu at ijm.jussieu.fr>
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Message-ID: <16133.19612.766626.404102 at akasha.ijm.jussieu.fr>
Date: Fri, 4 Jul 2003 11:45:00 +0200
To: lablgtk at kaba.or.jp
Cc: Richard Jones <rich at annexia.org>
Subject: Re: containers & subclasses of widgets
In-Reply-To: <20030703144931.GA29657 at clipper.ens.fr>
References: <20030703144222.GA15588 at redhat.com>
	<20030703144931.GA29657@clipper.ens.fr>

 Nicolas George [Thursday 3 July 2003] :
 >
 > Le quintidi 15 messidor, an CCXI, Richard Jones a écrit :
 > > I guess this comes down to the strange type system used by LablGtk.
 > 
 > No, it has to do with static typing. The children of a container
 > are widgets, nothing more: they could be labels, input boxes,
 > images, anything. The static type system of Caml has no way to know
 > that they will be vboxes.
 > 
 > You could use the dynamic type checking facilities of Gtk+ to
 > refine the widget into a vbox, but I believe this is a bad
 > style. If you need to do something to some widget, do not rely on
 > accessing it through its parents: store it in a variable with a
 > relevant name. This way you will have reliable static typing, and
 > your code will not break if you change the layout of your widgets.

Another way is to use the memo class from GUtil module.
It type is :

,----
| class ['a] memo : unit ->
|   object
|     constraint 'a = #widget
|     val tbl : (int, 'a) Hashtbl.t
|     method add : 'a -> unit
|     method find : widget -> 'a
|     method remove : widget -> unit
|   end
`----

In your case, since all widgets in your table are vbox, you only need
one memo object. Simply do a memo#add on your vbox before puting them
in the table. Them you can do
  List.map memo#find table#children
to get your vbox back.

-- 
   Olivier