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From: Florian Weimer <Florian.Weimer@RUS.Uni-Stuttgart.DE>
Newsgroups: comp.lang.ada
Subject: Re: Does a null pointer always raise Constraint_Error?
Date: 13 Dec 2000 15:58:14 +0100
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lutz@iks-jena.de (Lutz Donnerhacke) writes:

> * Ken Garlington wrote:
> >"Lutz Donnerhacke" <lutz@iks-jena.de> wrote in message
> >: * Robert Dewar wrote:
> >: [access to empty arrays represent as Null (System.Address)]
> >: >   subtype n is string (1 .. 0);
> >: >   type np is access n;
> >: >   a, b : np;
> >: >
> >: >   if a.all = b.all then ...
> >: >
> >: >it is a common compiler bug to translate this as
> >: >
> >: >   for j in n'range loop
> >: >     if a.all (j) = b.all (j) ....
> >: >
> >: >and the null loop causes no checks to be made :-)

> Possible, but irrelevant IMHO. Two empty arrays of the same component type
> are equal per definition.

There a two language-defined checks involved prior to the array
comparison.  However, 11.6(5) seems to permit the omission of these
checks, but I'm not sure about that.