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From: Michael Erdmann <michael.erdmann@snafu.de>
Newsgroups: comp.lang.ada
Subject: Re: Q: Endless loop by dispatching
Date: Fri, 11 Jul 2003 17:07:52 +0200
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To: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
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Xref: archiver1.google.com comp.lang.ada:40196
Date: 2003-07-11T17:07:52+02:00
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Dmitry A. Kazakov wrote:

>>Does any body know, what this loop causes?! I am not sure
>>if this is a bug or simply i missed the point.
> 
> 
> Serialize is class-wide and a view conversion does not change the
> tag..I.e. you have a re-dispatching case. Re-dispatching is a
> dangerous thing. [I would like it removed from Ada]
> 
> So Serialize re-dispatches to B.Write which again calls Serialize.
> From design point of view, one should never call class-wide routines
> from specific ones, this warranties that dispatch happens only once.
> 
> I suppose that you want sort of procedure expansion instead of
> complete overriding, if so, then you should explicitly call parent's
> Write, similarly as one does it for Initialize/Finalize:
> 
Unfortuantly this was not the complete code. The Serialize was itended
to do a  more complex job, which i have to replicate any where i want
to serialize an object. The original serialize code looks some what
like this:

procedure Serialize( This : in Object'Class ) is
   ........
    a := next(Attributes(This'Tag))
    while a /= null loop
        Write( this.all, a.id );
        a := next(....);
    end loop;

end;

The procedure write is a procedures which  writes out a selected 
attribute of an object. The procedure Serialize the complete
object. I would have been great when i could write something
like this in ada:

procedure Serialize( This : in Object'Class ) is

    Serialize( Super( This ) );

    a := next(Attributes(This'Tag))
    while a /= null loop
        Write( this.all, a.id );
        a := next(....);
    end loop;

end;


I think something like this does not exist in Ada!?


> package body B is
> ...
> procedure Write (This : in Object) is
> begin
> --       A.Serialize( A.Object( This ) );
>    A.Write (A.Object (This)); -- Write parent's things
>    Put_Line( "Q =" & Natural'Image(This.Q));
> end Write;
> 
> BTW, why do not you use Ada.Streams? It is for things like this.

I fact i am using Ada.Stream, but as i have written above the code was
simply a consended version.
> 
> ---
> Regards,
> Dmitry Kazakov
> www.dmitry-kazakov.de