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From: "Vinzent Hoefler" <nntp-2010-10@t-domaingrabbing.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada is getting more popular!
Date: Sat, 30 Oct 2010 02:01:46 +0200
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Date: 2010-10-30T02:01:46+02:00
List-Id: <comp.lang.ada>

On Fri, 29 Oct 2010 21:56:22 +0200, Yannick Duch=C3=AAne (Hibou57) <yann=
ick_duchene@yahoo.fr> wrote:

> I would enjoy to learn more about what's wrong with inheritance (I kno=
w
> this cannot model every thing of real life, but here the area is more
> restricted) and as much about classification without inheritance (I
> understand classification does not implies inheritance, but I would li=
ke
> to understand how and why inheritance should be avoided).

Just having inheritance is not really a problem. Basically you get inher=
itance
with each Ada subtype you derive from another, because the new subtype i=
nherits
the operation from its parent subtype:

     type Saturated_Integer is new Natural;

Thus, inheritance is very hard to avoid in Ada. Now suppose:

     function "+" (Left, Right : Saturated_Integer) return Saturated_Int=
eger
     is
     begin
        return
          Saturated_Integer (Saturated_Integer'Base (Left) +
                             Saturated_Integer'Base (Right));
     exception
        when Constraint_Error =3D>
           return Saturated_Integer'Last;
     end;

So, in the object oriented view the above already uses overriding and vi=
ew
conversion.

The problems start with the dynamic properties, where the operations on =
the
types can not be resolved statically anymore, because these are very har=
d
to prove for correctness. They may even call subroutines which are compl=
etely
out of the scope of the unit you're calling it from.

And if you don't want (or are not allowed, because the Software Programm=
er's
Manual says so) to use class-wide programming, then there's usually no p=
oint
in using inheritance at all. ;)

Well, I better shut up now, Jean-Pierre is the expert on that, I am just=
 a
user. ;)


Vinzent.

-- =

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