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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: How to test object hierarchy
Date: Fri, 19 Dec 2003 18:07:05 +0100
Organization: At home
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Hyman Rosen wrote:

> Dmitry A. Kazakov wrote:
>> You have to override Test_Hierarchy for each new type
> 
> Which brings a question to my non Ada-knowing mind.
> I know that for a subprogram to be dispatching, it
> must be defined in the same package (or immediately
> after?) as the tagged type upon which it dispatches.

Before the freezing point, which is informally at the first "non-trivial"
use of the type before the package specification end.

> Can an instantiation of a generic be dispatching in
> this way? Could I do (pardon the syntax errors)
>      procedure Test_Hierarchy is new
> Generic_Test_Hierarchy(Type1=>Derived_Object);
> rather than copy the code each time?

Aside, it is actually what inheritance is for! The problem is that there is
no [proper] multiple dispatch in Ada.

Well, an implementation of a dispatching subprogram through instantiation of
a generic one is not allowed in either Ada or C++. One step up. A generic
primitive operation is also not allowed in both. Another step up. Generic
types do exist in C++, but not in Ada, where same effect is achieved using
generic packages.

A strategic question is, whether one realy should exploit all possible
combinations of inheritance [and all other language things] and generics.
You know my opinion, down with generics! And there will be no question
anymore! (:-))

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de