Re: Enumeration representation

[Bryce Bardin <bbardin@home.com>]

Keith Thompson wrote:
> 
> Robert Dewar <robert_dewar@my-deja.com> writes:
> > In article <yecn1uu9xy2.fsf@king.cts.com>,
> >   Keith Thompson <kst@cts.com> wrote:
> >   If you try to read
> > > such a value from an external interface, it's very difficult
> > > to check that you've gotten a valid value without invoking
> > > erroneous execution (undefined behavior).
> >
> > No, it is quite easy, do an unchecked conversion of the value
> > into the enumeration variable, or just read the value in
> > directly with appropriate low level I/O, then do a 'Valid test.
> >
> > And Keith, before you go rummaging around legalise in the RM,
> > be sure to read the relevant AI, whose purpose is basically
> > to say, yes of course the above works, whatever the RM says :-)
> 
> Ok, I think you're right.
> 
> As I recall, a strict reading of the RM implies that the above obvious
> approach invokes erroneous execution, though a conforming
> implementation would have to be somewhat perverse to make it do
> anything other than the obvious.  (I think you could avoid
> erroneousness by wraping the enumeration variable in a record.)  Given
> the AI (whose status I haven't followed lately), such an
> implementation would have to be both perverse and non-conforming --
> hopefully an unlikely combination.
> 
> Do you happen to remember the AI number?  I'm pretty sure it was based
> on a comment I submitted.

AI95-00167/01, which is proposed to be a binding interpretation, but is
not yet written up in final form nor approved by either the ARG or WG9, 
as far as I know.

<snip>

Bryce Bardin