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Message-ID: <16051.59001.830936.263287 at karryall.dnsalias.org>
Date: Sat, 3 May 2003 17:55:37 +0200
From: Olivier Andrieu <andrieu at ijm.jussieu.fr>
To: Richard Jones <rich at annexia.org>
Cc: lablgtk at kaba.or.jp
Subject: Re: More GtkHtml questions
In-Reply-To: <20030503100346.GE24136 at redhat.com>
References: <20030503100346.GE24136 at redhat.com>

 Richard Jones [Saturday 3 May 2003] :
 >
 > How does garbage collection work in lablgtk? It looks like my object
 > will never get freed up.

The GtkObjects are wrapped in ML custom blocks. When the ML value is
garbage collected, it calls a finalization function which is
gtk_object_unref. 

You should wrap gtk_html_new like this :

  ML_0(gtk_html_new, Val_GtkAny_sink)

the `_sink' thing is a peculiarity of GTK reference counting mechanisms
("floating" references) and only applies to newly created objects.

 > Also, the type system is very confusing. I have GtkHtml which is
 > derived in this hierarchy:
 > 
 > Widget
 >   -> Container
 >     -> Layout
 >       -> GtkHtml
 > 
 > so now I'm defining:
 > 
 > type html = [widget|`container|`layout|`html]
 > 
 > (These variant types are very much at the edge of my experience with
 > OCaml - the manual is very unhelpful when it comes to explaining
 > exactly what the ` backquote is all about).
 > 
 > Is this correct?

Yes. In fact since there is already a layout type defined (in gtk.ml),
you could even write :
  type html = [layout|`html]
which is the same as :
  type html = [`base|`widget|`container|`layout|`html]

The backquote is the syntax for polymorphic variants constructors. For
a regular variant it is :
  type foo = BAR | BAZ
and for the polymorphic versions :
  type foo = [`BAR | `BAZ]

But mind that these types are only used as parameters for the
(abstract) type Gtk.obj. These are phantom types : there are no actual
values, the constructor `layout is never used to create a value, it
only appears in type expressions.  The point is to benefit of the
subtyping relations between these polymorphic variant types.

For instance, functions wrapping the GtkLayout methods take as first
argument a [>`layout] obj , that means any obj with at least the
`layout type. Thus all GtkLayout functions can be applied to html obj
since html "extends" the layout type.

 > Now to define my class:
 > 
 > class html obj = object
 >   inherit GPack.layout (obj : GtkHtml.html obj)
 > end
 > 
 > Except this doesn't actually work. I get:
 > 
 > File "gHtml.ml", line 40, characters 24-27:
 > This expression has type GtkHtml.html Gtk.obj but is here used with type
 >   Gtk.layout Gtk.obj
 > Type GtkHtml.html = [ `base | `container | `html | `layout | `widget]
 > is not compatible with type
 >   Gtk.layout = [ `base | `container | `layout | `widget]
 > 
 > Ideas?

see Jun explanation. This change is already done in lablgtk2.

-- 
   Olivier