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From: Larry Hazel <lhhazel@otelco.net>
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Newsgroups: comp.lang.ada
Subject: Re: Dynamic dispatch again
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Date: Mon, 08 Oct 2001 20:29:20 -0500
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Date: 2001-10-08T20:29:20-05:00
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Darren New wrote:
> 
> tmoran@acm.org wrote:
> >
> > >Right now, my alternative is ... .  Ugly.
> >   I've *always* found that if something was ugly/difficult in Ada,
> > after some thought it would become clear that the approach was in
> > fact a poor one, and a different approach, which worked nicely in
> > Ada, was a better one.  (Not to say that this alternative nice
> > approach in this case is obvious. ;)
> 
> Well, that's kind of why I'm posting here. I'm not sure what the right
> approach to dynamically dispatching an entry to one of N different tasks
> might be. Someone earlier mentioned using "requeue", but that seems to
> suffer the same problems. I've thought of any number of different
> approaches, and they're all ugly, since the point is to have a bunch of
> different tasks running, and all the alternate approaches involve not
> dealing with tasks.
> 
> It seems Ada isn't quite as orthogonal as could be hoped.

I'm not sure I understand what you are trying to do.  What I am going to suggest
is somewhat ugly to an Ada person and may be compiler dependent, but I don't
think so.  If the task specs are all the same:

with Unchecked_Conversion;
...
...
   task type A is
      -- common spec
   end A;
   type A_Access is access A;

   type Task_Array is array(1..How_Many) of A_Access;

   task type B is
      -- common spec
   end B;
   type B_Access is access B;

   function Coerce is new Unchecked_Conversion (B_Access, A_Access);

etc.

   Tasks : Task_Array := (new A, Coerce(new B), ....);

I've seen this work in Ada 83 with the VADS compiler.

Larry