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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: operation can be dispatching in only one type
Date: Tue, 24 Nov 2015 13:18:06 -0700
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Date: 2015-11-24T13:18:06-07:00
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On 11/24/2015 11:37 AM, Serge Robyns wrote:
> 
> This is what I get with gnat2015:
> type derived from untagged type cannot have extension
> 
> for:
>    type T_Control is record
>       Name : T_Control_Name;
>    end record;
> 
>    type T_Counter_Control is new T_Control with record
>             Counter : Natural;
>    end record;

Yes, only a tagged type can be extended (and any derivation from a tagged type
requires an extension), but a new type can be derived from any type:

type Control_Info is record
   Active : Boolean;
end record;

type External_Control is new Control_Info;
for External_Control use record
   Active at 1 range 3 .. 3;
end record;

> 
> I agree and so far the need is limited.  However I do love the obj.method notation which was my initial reason for using tagged types everywhere.  And I do expect needs on the business objects, like indeed finalization and a few specializations.  True back in the 80's we did those 'tricks' without any OO language.  Hence facing such issues now will avoid me to re-design the whole thing later on because of an oversight due to lack of Ada experience.  This is my biggest fear for me; to pursue my project in Ada rather than to go more for my older friends.  I'm more the guy that should read Ada for the C programmer with some experience in old C++ and Java.  And besides this group, I know no one using Ada.

Have you looked at /Ada Distilled/? It is Ada for the experienced programmer.

-- 
Jeff Carter
"Whatever it is, I'm against it."
Horse Feathers
46