Re: 'withing' problem

[dewar@gnat.com (Robert Dewar)]

"David Crocker" <dcrocker@imsltd.com> wrote in message news:<3be27344$0$227$ed9e5944@reading.news.pipex.net>...
> Are there any commercial compilers with language 
> extensions to work around the infamous "withing" problem?

Yes, GNAT Pro implements a version of the "with type" proposal that
was made some time ago to solve this problem.
 
> I am also aware that GNAT implements a workaround

This is not a "work around" but rather a language extension
feature that directly addresses the problem.

> but what we really need is a validated compiler

The presence of extensions in a compiler does not mean the
compiler cannot be validated, providing that there is a way
to turn off the extensions, as is the case with GNAT Pro.

> I heard that the next update to the Ada language circa 
> 2005 will address the problem, but this is too far away 
> to be any consolation. Surely we can't be
> the only company that needs the problem fixed urgently?

The only way to have an "urgent" fix to this problem is
to go with implementation extensions of the kind in GNAT
Pro. Yes, they won't be fully portable to other compilers,
but there is no immediate urgent short term solution that
will solve that. Note that the ARG is still discussing the
preferred long-term solution, and has recently been examining entirely
different approaches. The sequence of
events is that first the ARG approves a detailed proposal,
the WG2.1 approves it, then it appears in an official
addendum. Even the first step is a way off, and so I do not
expect vendors to be implementing a common solution anytime
soon, and indeed, even if the ARG does approve a solution,
that is no guarantee that any vendor will implement it on
any particular time schedule.

> How do developers of large military software systems 
> manage?

Well at least for our customers, they use the feature we
have provided in GNAT Pro. This feature was not implemented
for our amusement, but rather in response to serious customer needs.

Robert Dewar
Ada Core Technologies