From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on
	ip-172-31-74-118.ec2.internal
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.5-pre1
Path: eternal-september.org!reader02.eternal-september.org!news.mixmin.net!proxad.net!feeder1-2.proxad.net!cleanfeed3-a.proxad.net!nnrp1-1.free.fr!not-for-mail
Newsgroups: comp.lang.ada
References: <606f5938$0$27421$426a74cc@news.free.fr>
 <s4o00c$sne$1@gioia.aioe.org>
From: DrPi <314@drpi.fr>
Subject: Re: GtkAda : Trying to derive a widget
Date: Fri, 9 Apr 2021 07:28:46 +0200
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.9.0
MIME-Version: 1.0
In-Reply-To: <s4o00c$sne$1@gioia.aioe.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: fr
Content-Transfer-Encoding: 8bit
Message-ID: <606fe610$0$3717$426a74cc@news.free.fr>
Organization: Guest of ProXad - France
NNTP-Posting-Date: 09 Apr 2021 07:28:48 CEST
NNTP-Posting-Host: 82.65.30.55
X-Trace: 1617946128 news-1.free.fr 3717 82.65.30.55:53141
X-Complaints-To: abuse@proxad.net
Xref: reader02.eternal-september.org comp.lang.ada:61762
List-Id: <comp.lang.ada>

Le 09/04/2021 à 00:27, Dmitry A. Kazakov a écrit :
> 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);
I did try this notation and got this error :
debug_panel.adb:6:07: invalid prefix in selected component "Debug_Panel"
debug_panel.adb:6:18: prefixed call is only allowed for objects of a 
tagged type

I've just realized this is because the package and the access type have 
the same name.

> 
> 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.
> 
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.

> 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 ?

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

Thanks for your help