From: mab@dst17.wdl.loral.com (Mark A Biggar)
Subject: Re: Rules for Representation of Subtypes
Date: 1996/09/27
Date: 1996-09-27T00:00:00+00:00 [thread overview]
Message-ID: <52hnvh$li0@wdl1.wdl.lmco.com> (raw)
In-Reply-To: DyEr6p.38H@world.std.com
In article <DyEr6p.38H@world.std.com> bobduff@world.std.com (Robert A Duff) writes:
>In article <1996Sep26.191257.1@eisner>,
>Larry Kilgallen <kilgallen@eisner.decus.org> wrote:
>>Like:
>> if X'Valid
>>? I would think that as being an argument in _favor_ of declaring
>>the C-updated object in a tightly constrained fashion.
>No, that won't work. By the time you get to that if statement, the
>program execution is already erroneous. Compilers can and do (and
>should) take advantage of that fact to generate faster code that doesn't
>work. An unchecked conversion is a function call, and there's no way to
>capture the result of it without assigning it somewhere, which causes
>erroneousness if the result is bad.
I'm not sure about this as I always thought that the RM was pretty clear
that only the USE of an abnormal value was erroneous, but that simply
assigning it was safe, at least I'm sure that was the intent, otherwise
X'VALID after an unchecked conversion is useless, but that is one of the
explisit examples of its intended use in the RM.
--
Mark Biggar
mab@wdl.lmco.com
next prev parent reply other threads:[~1996-09-27 0:00 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
1996-09-22 0:00 Rules for Representation of Subtypes Matthew Heaney
1996-09-23 0:00 ` David C. Hoos, Sr.
1996-09-23 0:00 ` Samuel T. Harris
1996-09-26 0:00 ` David C. Hoos, Sr.
1996-09-23 0:00 ` Robert A Duff
1996-09-24 0:00 ` Robert Dewar
1996-09-24 0:00 ` Robert Dewar
1996-09-26 0:00 ` Keith Thompson
1996-09-26 0:00 ` Matthew Heaney
1996-09-27 0:00 ` Robert A Duff
1996-09-27 0:00 ` Robert Dewar
1996-09-27 0:00 ` Robert Dewar
1996-09-27 0:00 ` Robert A Duff
1996-09-23 0:00 ` Robert A Duff
1996-09-24 0:00 ` Matthew Heaney
1996-09-26 0:00 ` Robert A Duff
1996-09-26 0:00 ` Larry Kilgallen
1996-09-27 0:00 ` Robert A Duff
1996-09-27 0:00 ` Mark A Biggar [this message]
1996-09-30 0:00 ` Robert A Duff
1996-10-01 0:00 ` Larry Kilgallen
1996-10-01 0:00 ` Robert A Duff
1996-10-01 0:00 ` Samuel Tardieu
1996-10-01 0:00 ` Ken Garlington
1996-10-01 0:00 ` Valid Attribute and Unchecked Conversion Matthew Heaney
1996-10-02 0:00 ` Robert A Duff
1996-10-04 0:00 ` Keith Thompson
1996-10-04 0:00 ` Robert A Duff
1996-10-04 0:00 ` Robert Dewar
1996-10-11 0:00 ` Norman H. Cohen
1996-10-12 0:00 ` Robert Dewar
1996-10-06 0:00 ` Keith Thompson
1996-10-07 0:00 ` Robert Dewar
1996-10-09 0:00 ` Keith Thompson
1996-10-07 0:00 ` Ken Garlington
1996-10-08 0:00 ` Alan Brain
1996-10-04 0:00 ` Matthew Heaney
1996-10-07 0:00 ` Robert Dewar
1996-10-09 0:00 ` Keith Thompson
1996-10-07 0:00 ` Robert Dewar
1996-10-10 0:00 ` Ken Garlington
1996-10-11 0:00 ` Robert Dewar
1996-10-14 0:00 ` Keith Thompson
1996-10-14 0:00 ` Ken Garlington
1996-10-07 0:00 ` Kenneth Almquist
1996-09-28 0:00 ` Rules for Representation of Subtypes Larry Kilgallen
1996-09-29 0:00 ` Robert A Duff
1996-09-29 0:00 ` Matthew Heaney
1996-09-30 0:00 ` Robert Dewar
1996-09-30 0:00 ` Matthew Heaney
1996-09-30 0:00 ` Robert A Duff
1996-09-29 0:00 ` Larry Kilgallen
1996-09-29 0:00 ` Matthew Heaney
1996-09-30 0:00 ` Robert A Duff
1996-10-01 0:00 ` Ken Garlington
1996-10-02 0:00 ` Robert A Duff
1996-10-02 0:00 ` Ken Garlington
1996-10-06 0:00 ` Robert Dewar
1996-10-03 0:00 ` Robert Dewar
1996-10-02 0:00 ` Valid Attribute and Unchecked Conversion George Haddad
1996-10-03 0:00 ` John Herro
1996-10-04 0:00 ` Karl Cooper {46901}
1996-10-07 0:00 ` Mark A Biggar
1996-10-08 0:00 ` Robert Dewar
1996-10-05 0:00 ` Robert Dewar
1996-10-06 0:00 ` Keith Thompson
1996-10-14 0:00 ` Robert A Duff
1996-10-02 0:00 ` Robert I. Eachus
1996-10-02 0:00 ` Matthew Heaney
1996-09-27 0:00 ` Rules for Representation of Subtypes Matthew Heaney
1996-09-27 0:00 ` Robert A Duff
-- strict thread matches above, loose matches on Subject: below --
1996-09-28 0:00 Robert Dewar
1996-09-29 0:00 ` Robert A Duff
1996-09-29 0:00 ` Matthew Heaney
1996-09-28 0:00 Robert Dewar
1996-09-30 0:00 ` Keith Thompson
1996-09-28 0:00 Robert Dewar
1996-09-29 0:00 ` Robert A Duff
1996-09-29 0:00 ` Matthew Heaney
1996-09-29 0:00 ` Robert Dewar
1996-09-30 0:00 ` Art Schwarz
1996-09-30 0:00 ` Robert A Duff
1996-10-01 0:00 ` Larry Kilgallen
1996-10-01 0:00 ` Robert A Duff
1996-10-01 0:00 ` Brian R. Hanson
1996-10-02 0:00 Franco Mazzanti
1996-10-03 0:00 ` Robert A Duff
1996-10-03 0:00 Franco Mazzanti
1996-10-03 0:00 ` Robert A Duff
1996-10-10 0:00 W. Wesley Groleau (Wes)
1996-10-10 0:00 ` Robert Dewar
1996-10-11 0:00 ` Ken Garlington
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