Re: Ada is getting more popular!

["Vinzent Hoefler" <nntp-2010-10@t-domaingrabbing.de>]

On Fri, 29 Oct 2010 21:56:22 +0200, Yannick Duchêne (Hibou57) <yannick_duchene@yahoo.fr> wrote:

> I would enjoy to learn more about what's wrong with inheritance (I know
> 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 like
> to understand how and why inheritance should be avoided).

Just having inheritance is not really a problem. Basically you get inheritance
with each Ada subtype you derive from another, because the new subtype inherits
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_Integer
     is
     begin
        return
          Saturated_Integer (Saturated_Integer'Base (Left) +
                             Saturated_Integer'Base (Right));
     exception
        when Constraint_Error =>
           return Saturated_Integer'Last;
     end;

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

The problems start with the dynamic properties, where the operations on the
types can not be resolved statically anymore, because these are very hard
to prove for correctness. They may even call subroutines which are completely
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 Programmer's
Manual says so) to use class-wide programming, then there's usually no point
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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