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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Silly and stupid post-condition or not ?
Date: Mon, 6 Feb 2012 20:11:09 -0600
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2012-02-06T20:11:09-06:00
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"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wccwr81fi7a.fsf@shell01.TheWorld.com...
> "Randy Brukardt" <randy@rrsoftware.com> writes:
>
>> People forget that Ada uses "access types" rather than "pointers",
>
> A rose by any other name...
>
>>...and the
>> reason for that is that access types are type-safe (in the absence of
>> erroneous execution, anyway).
>
> That's like saying, "Drunk driving is safe so long as you don't crash."
>
> Type safety means "can't cause erroneous (unpredictable, undefined)
> execution".

Are you claiming that Ada is never type-safe? Since there are lots of ways 
to create erroneous execution in Ada, there is nothing in Ada that is 
remotely safe from it. (All real Ada programs are erroneous, after all.)

In any case, my point was about *outside* erroneous execution. Access types 
themselves are type-safe. If you start using Unchecked_ programming or 
address overlays or foreign language interfaces, you're outside of the box, 
but you can't blame that on the access types and values. (And please keep in 
mind that I was specifically postulating that the program was using a custom 
storage pool; the idea being that it could detect/prevent dangling pointers 
and thus eliminate that particular problem from causing erroneousness.)

                                          Randy.