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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Q: Memory management
Date: 1996/06/25
Message-ID: <DtK5LL.G65@world.std.com>#1/1
X-Deja-AN: 162066270
references: <9606241936.AA11042@most>
 <uvvg27kjm35.fsf@chaq.informatik.uni-tuebingen.de>
organization: The World Public Access UNIX, Brookline, MA
newsgroups: comp.lang.ada
Date: 1996-06-25T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <uvvg27kjm35.fsf@chaq.informatik.uni-tuebingen.de>,
Hannes Haug  <Hannes.Haug@Student.Uni-Tuebingen.de> wrote:
>    Wes> X'Address and X(X'First)'Address should be identical, too,
>    Wes> unless ...
>
>Is this true if you deal with unconstrained arrays ?

13.3(14) says X'Address should point at the first component of the
array.  This is "merely" Implementation Advice.  But I don't see any
reason why a compiler would not obey -- and if it didn't, I would
consider it a bug.

>... The bounds have
>to be stored at the beginning of the array.

They don't *have* to be.  That's just the typical implementation of
access-to-unconstrained-arrays.  I believe GNAT doesn't do it that way,
though.  On the other hand, the typical implementation of an
unconstrained array formal parameter is to pass the bounds separately
from the data, and to pass the data by reference.

>... I think that X'Address
>would give you the address of the location where the bounds are stored.

Some Ada 83 compilers did this.  In Ada 95, however, it should not be
true.

On the other hand, if you have discriminants or a Tag field, then the RM
doesn't say anything.  See 13.3(14.a).

- Bob