Date: Thu, 11 Aug 2005 01:23:45 -0300
From: romildo at uber.com.br
To: lablgtk at math.nagoya-u.ac.jp
Subject: [newbie] Creating widget classes
Message-ID: <20050811042345.GA29721 at malaquias>
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Hello.

I am starting to use the lablgtk library and
have some basic questions.

I have seen some examples of new widget classes
defined as in the following example:

class my_button ?label ?packing () =
  let button = GButton.button ?label ?packing () in
object (self)
  inherit GObj.widget button#as_widget
  method relabel new_label =
    button#set_label new_label
  method print =
    print_string (button#label);
    print_newline ()
end

If I am not wrong, the button variable introduced
by the let binding is common to all instances
of the class (class variable). Then if it is
changed (with button#set_label, for instance)
for an object, it would be changed for all
existing objects which are instances of the
my_button class. Therefore this class would
not work. But it works. I do not understand
why. Any explanation?

A correct definition would have button
as an instance variable:

class my_button ?label ?packing () =
object (self)
  val button = GButton.button ?label ?packing ()
  (* ...... *)
end

but then I do not now how to specify the
inheritance on GObj.widget

Is the definition of new widget classes
discussed somewhere?

Romildo