Re: Representation clauses and streams

[Tucker Taft <stt@averstar.com>]

Florian Weimer wrote:
> 
> Robert Dewar <robert_dewar@my-deja.com> writes:
> 
> > > Is there any reason why GNAT
> > > ignores the implementation advice 13.13.2(17)?
> >
> > GNAT is NOT ignoring this advice
> 
> Yes, you're right.  I missed the words `base range' (or didn't understand
> their implications).  I'm sorry about that.

As Robert mentioned, this implementation advice is in the middle
of revision by the Ada Rapporteur Group (ARG) of the ISO Working
Group 9.  The new advice will specify the "first subtype range"
rather than the "base range," as the first subtype range is
portable across implementations, and seems to match users' expectations
better.  

Note that this will mean that certain values of
the "base" subtype T'Base may raise Constraint_Error when
passed to T'Write.  This is currently felt by the ARG to be a reasonable
tradeoff.  Apparently GNAT has not yet been revised to
follow the updated advice, which is quite reasonable given
that the associated AI, AI-195, is still a work-item -- it
is not yet officially "approved."  For the full AI, see:

    http://www.ada-auth.org/cgi-bin-acats/cvsweb.cgi/AIs/AI-00195.DOC

and select revision 1.10.

-Tucker Taft  stt@averstar.com