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From: kilgallen@eisner.decus.org (Larry Kilgallen)
Subject: Re: Rules for Representation of Subtypes
Date: 1996/09/28
Message-ID: <1996Sep28.155354.1@eisner>#1/1
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references: <mheaney-ya023080002209961353500001@news.ni.net>
 <mheaney-ya023080002409960726040001@news.ni.net> <DyCF97.7zp@world.std.com>
 <1996Sep26.191257.1@eisner> <DyEr6p.38H@world.std.com>
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newsgroups: comp.lang.ada
Date: 1996-09-28T00:00:00+00:00
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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.

If the assignment of the output causes erroneousness,
then why isn't the name of the operation Checked Conversion ?

Larry Kilgallen