Re: GtkAda : Trying to derive a widget

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2021-04-09 13:42, DrPi wrote:
> Le 09/04/2021 à 08:18, Dmitry A. Kazakov a écrit :

>> Debug_Panel belongs to both Debug_Panel_Record'Class and 
>> Gtk_Scrolled_Window_Record'Class (and many other classes), so the 
>> ambiguity.
>>
> Surprising behaviour for a strongly typed language but there surely is a 
> good reason.

It is strongly typed.

The class is defined a set of types closed upon inheritance. When you 
declare a class-wide operation like Initialize it is meant to work on 
all instances of the class. There is no type violation or type coercion 
here.

Initialize of Gtk_Scrolled_Window_Record'Class is defined on 
Gtk_Scrolled_Window_Record and all types derived from 
Gtk_Scrolled_Window_Record.

When you declare another Initialize on Debug_Panel_Record'Class it is 
defined on Debug_Panel_Record and all its descendants.

If you overload them, in a context you must disambiguate for 
Debug_Panel_Record and any descendant of.

This is not different from Ada subtypes. For example, you can declare

    procedure Foo (I : Integer);

and in some other package

    procedure Foo (I : Positive);

If both become visible in a context you would have same problem.

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