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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Self pointer in limited record
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Date: Thu, 6 Sep 2007 09:37:34 +0200
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Date: 2007-09-06T09:37:03+02:00
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On Wed, 05 Sep 2007 23:38:34 +0200, Georg Bauhaus wrote:

> They can avoid surprises and nasty issues because they enforce body
> visibility of data objects. Example:
> 
> <start of declarative part>
> 
>         package S is
>                 type T is limited private;
>                 procedure op(x: in out T);
>         private
>                 type T is limited record
>                         null;
>                 end record;
>         end S;

This is IMO bad design, it should be:

package S is   -- Stateless
   type T is limited private;
   ...
end S;

package Data is -- Stateful
   ... -- Operations having an instance of T as a hidden parameter
end Data;

with S;
package body Data is
   Singleton : S.T;
   ...
end Data;

There is no need to "with" S for anybody else, provided that Singleton as
an object indeed has no public interface. Otherwise it has to be typed
anyway. You can also move T to the private part of Data or to its body, but
you should never expose it.

-----------------
I don't know if "true" typeless singletons exist. It is difficult to find
one. Clock is *a* Time-valued function, current thread is *a* task,
Gravitational constant is *a* floating-point number. 

Theological dispute.

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