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From: kilgallen@eisner.decus.org (Larry Kilgallen)
Subject: Re: Rules for Representation of Subtypes
Date: 1996/10/01
Message-ID: <1996Oct1.100608.1@eisner>#1/1
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references: <DyCF97.7zp@world.std.com> <1996Sep26.191257.1@eisner>
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Date: 1996-10-01T00:00:00+00:00
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In article <DyKC85.Gqx@world.std.com>, bobduff@world.std.com (Robert A Duff) writes:

> The point is that you should convert to a type that "fills all the
> bits".  That is, there are no possible bit patterns that don't represent
> valid data.  Then, *after* the unchecked conversion, you can do an
> assignment that does a constraint check.  Checking Y'Valid in the above
> example would not help, since the program is already erroneous.  The
> 'Valid feature is just like anything else -- it won't work as advertised
> if the execution is already erroneous.

So can someone give an example of how Z'Valid _might_ be useful
after an unchecked conversion, as seems to be indicated by the
Reference Manual.

Larry Kilgallen