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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Redispatching
Date: Thu, 17 Apr 2014 09:26:02 +0200
Organization: cbb software GmbH
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Date: 2014-04-17T09:26:02+02:00
List-Id: <comp.lang.ada>

On Wed, 16 Apr 2014 22:53:28 +0300, Niklas Holsti wrote:

> On 14-04-16 12:30 , J-P. Rosen wrote:
>> As far as redispatching is concerned: since a method is linked to a
>> single class, there should be no redispatching.
> 
> (I think you meant to write "linked to a single type", not "class".)
> 
> Then you must also be of the opionion that there should be no
> inheritance of methods, because inheritance makes the same method become
> linked to different types. Is that your view?

It is confused. A primitive operation (method) is defined on (linked to)
the whole class T'Class. Its specific body is defined on a specific type
S<:T.

Re-dispatch does not violate the contract of the primitive operation, it
potentially does the contract of the *type-specific* body where re-dispatch
happens.

BTW, it is not just re-dispatch. I would argue that when you call a
parent's implementation from the body you also potentially violate the
contract:

procedure F (X : in out S) is
begin
   ...
   F (T (X)); -- Parent's implementation
   ...
end F;

Of course here potential harm is much lesser than in the case of
re-dispatch.

In short, we know that type coercion is bad, don't we?

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de