Re: GtkAda : Trying to derive a widget

["J-P. Rosen" <rosen@adalog.fr>]

Le 09/04/2021 à 07:28, DrPi a écrit :
>> Without "use" Initialize is unambiguous.
>>
> That makes sense.
> However, I don't understand why there is ambiguity when using "use".
> Debug_Panel (the type) is of type Debug_Panel_Record, so Initialize 
> should resolve to the one using this type. Well, I guess I'm wrong.
No, the type is "access Debug_Panel_Record'Class", and the other 
initialize is for "access Gtk_Scrolled_Window_Record'Class", which 
covers the other one.

Remember that a class wide type ('Class) is a different type that covers 
all descendants.

>> 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;
> 
> I'm surprized this is possible to write such a thing in Ada.
> What does the compiler do with this ?
> There is no problem, since 
Gtk.Scrolled_Window.Gtk_Scrolled_Window_Record is a descendant of 
Gtk.Widget.Gtk_Widget_Record. There is no lie: a Debug_Panel_Record IS A 
Gtk_Widget_Record. The private view has more information: it actually IS 
A Gtk_Scrolled_Window_Record, but the extra properties are not 
accessible outside from the package body.

-- 
J-P. Rosen
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