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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: GtkAda : Trying to derive a widget
Date: Fri, 9 Apr 2021 00:27:26 +0200
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On 2021-04-08 21:27, DrPi wrote:

> I'm trying to create a GtkAda widget derived from a standard widget.
> 
> -- debug_panel.ads
> with Gtk.Scrolled_Window; use Gtk.Scrolled_Window;
> with Gtk.Text_View;       use Gtk.Text_View;
> 
> package Debug_Panel is
> 
>    type Debug_Panel_Record is new Gtk_Scrolled_Window_Record with private;
>    type Debug_Panel is access all Debug_Panel_Record'Class;
> 
> 
>    procedure Gtk_New (Panel : in out Debug_Panel);
>    procedure Initialize (Panel : not null access Debug_Panel_Record'Class);
> 
> private
> 
>    type Debug_Panel_Record is new Gtk_Scrolled_Window_Record with record
>       Text       : Gtk_Text_View;
>    end record;
> 
> end Debug_Panel;
> 
> 
> -- debug_panel.adb
> package body Debug_Panel is
> 
>    procedure Gtk_New (Panel : in out Debug_Panel) is
>    begin
>       Panel := new Debug_Panel_Record;
>       Initialize (Panel);

    Debug_Panel.Initialize (Panel);

Another way would be to remove "use Gtk.Scrolled_Window" and declare as

    type Debug_Panel_Record is
       new Gtk.Scrolled_Window.Gtk_Scrolled_Window_Record with private;

Without "use" Initialize is unambiguous.

P.S. When you create new widget it is better to use a more general 
ancestor hiding insufficient details, e.g.

    type Debug_Panel_Record is
       new Gtk.Widget.Gtk_Widget_Record with private;
    ...
private
    type Debug_Panel_Record is
       new Gtk.Scrolled_Window.Gtk_Scrolled_Window_Record with
    record
       ...
    end record;

This makes the code less fragile if you later decide to choose another 
container widget for the base.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de