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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: To Initialise or not
Date: 1996/05/08
Message-ID: <Dr3yzz.52C@world.std.com>#1/1
X-Deja-AN: 153822202
references: <318508FE.204B@sanders.lockheed.com>
 <318E43A4.390E@lmtas.lmco.com> <Dr0Ioq.7o3@world.std.com>
 <31909E74.1E09@lmtas.lmco.com>
organization: The World Public Access UNIX, Brookline, MA
newsgroups: comp.lang.ada
Date: 1996-05-08T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <31909E74.1E09@lmtas.lmco.com>,
Ken Garlington  <garlingtonke@lmtas.lmco.com> wrote:
>Robert A Duff wrote:
>> 
>> Well, sort of.  The use of an invalid representation will not
>> necessarily be detected in all cases.
>
>In what case would 'Valid not detect an invalid representation?

Heh?  I said, "all cases".  The 'Valid attribute is *one* case.  I
meant, pragma Normalize_Scalars will not cause every read of an
uninitialized scalar to be detected.  Am I confused?  I thought we were
talking about pragma Normalize_Scalars, not the 'Valid attribute.

>For scalar X, X'Valid "yields True if and only if the object
>denoted by X is normal and has a valid representation."

Yes.  But be careful -- anything that's erroneous will negate that rule.

>Certainly, if there is _no_ invalid representation of X, then
>'Valid won't detect any. However, you should be able to use 'Size
>to force the existence of an invalid representation for any
>scalar, right?

No, I don't think so.  An implementation might allow it, but where does
the RM require an implementation to accept such a Size clause?  (Note:
The ARG is considering some AI's related to this issues, notably AI's 51
and 109, in case you care to comment.)

- Bob