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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Dispatching problem.
Date: Mon, 10 Feb 2003 10:12:13 +0100
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On 7 Feb 2003 06:55:49 -0800, petter.fryklund.konsult@dynamics.saab.se
(Petter Fryklund) wrote:

>Another way to explain our problem: a message (of which there are
>several variants) is received from another system in unit P. It is
>forwarded to unit B which decodes to message using procedures in
>package A. Package A can also be used for coding of outbound messages
>and for producing trace of messages contents, both inbound and
>outbound. We would like to dispatch both coding and tracing in A and
>subsequent usage of the decoded message in B. Perhaps inbound messages
>and outbound should be treated differently? In the original post there
>is a 1-to-1 relationship between ie B.B1 and A.M1. They have the same
>contents, apart from the tag. So, how do make an A.M1 a B.B1 (or
>really an A.Msg a B.Msg?)so that we can dispatch in code written in
>package B? (Dispatching in B ;-)

First of all, Ada does not have multiple inheritance, so B.Msg have to
be in A.Msg. What is wrong with the following design?

package A is
   type Msg is abstract tagged null record;
   procedure Y (X : in out Msg) is abstract;

   type M1 is new Msg with ...;
   procedure Y (X : in out Msg);

   type M2 is new Msg with ...;
   procedure Y (X : in out Msg);
end A;

with A;
package B is
   type M1 is new A.M1 with ...;
   procedure Y (X : in out M1);

   type M2 is new A.M2 with ...;
   procedure Y (X : in out M2);
end B;

BTW, the package B looks superfluos, as it possibly is, if you are
saying that A.Mi = B.Mi.

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