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From: Brian Rogoff <bpr@shell5.ba.best.com>
Subject: Re: Subverting 'Access for Sub-programs
Date: 1999/08/04
Message-ID: <Pine.BSF.4.10.9908042121260.29130-100000@shell5.ba.best.com>#1/1
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References: <37A71EF1.2201@dera.gov.uk> <37A7FDE8.4F5@dera.gov.uk>
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Date: 1999-08-04T00:00:00+00:00
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On Wed, 4 Aug 1999, Robert A Duff wrote:
> Anton Gibbs <agibbs@dera.gov.uk> writes:
> 
> > Here, the problem is retaining visibility of the parameter F within the
> > procedure whose 'Access I am trying to pass to the Perform operation. If
> > I move Print_If_Multiple out to its own package (ie. out of the scope of
> > Not_Main) then the only way I can see F is by using global data. I know
> > this will work but I am reluctant to adopt this approach because I have
> > often found that non-re-entrant code bites back in years to come when it
> > gets re-used (usually by me) in a way the author never originally
> > intended.
> 
> There is no good solution to this problem: no solution that is portable,
> concise, reentrant, &c.
> 
> One thing you can do is declare a tagged type, and use an extension as
> the environment of the procedure you want to pass -- then instead of
> passing a procedure as a parameter, pass an object of the class-wide
> type.

This workaround would be a lot more effective if you could extend the
tagged type at a deeper accessibility level than the parent. But you know 
that :-)

-- Brian