RE: [vhdl-200x] Corrections to Minutes for VHDL-200X-FT meeting,S an Jose Dec 4, 2003

Subject: RE: [vhdl-200x] Corrections to Minutes for VHDL-200X-FT meeting,S an Jose Dec 4, 2003
From: Matthias Wächter (
Date: Thu Dec 18 2003 - 01:19:50 PST


On Wed, 17 Dec 2003, Bailey, Stephen wrote:
> The suggestion, and I was not privy to your reply to Jim, was to
> extend the use of implied conversions to expressions, when this
> language change was previously proposed as "only allowed in
> conditions".
> If the proposal said this, it was a mistake. We specifically
> discussed the problems with implicit conversions applied anywhere in
> an expression back in July and knew this would cause all kinds of
> problems. That is why we decided we needed to limit it to the
> top-level of the expression and only within the context that the
> language recognizes as a *condition*.

If I understand Andy correctly (and if not, then that's my opinion), he is
sure that limiting the implicit conversion to the *condition* will by
itself lead to confusion at people using this feature. They will say: Hey,
if VHDL is _that_ cool, why not have implicit conversion in the
*expressions* as well? And -then!- the problem is here: (1) We cannot
remove the feature anymore, (2) the pressure on standardizing Verilog-like
implicit conversions in *expressions* will get higher, and the next
proposal will be that VHDL allows implicit boolean equivalence within
expressions. Then we have Verilog-VHDL.

Of course, ensuring backward compatibility allows Andy, me and all other
guys with a fable for strong typing to write "if cond = '1' then" in our
closed chambers. But the issues here are, especially in the aerospace
industry, proofreading, verification, certification, and not to forget,
composability. And the less ambiguous the code is, the faster it is to
read and to verify. You not always have to deal with your own code in the
real world.

- Matthias Waechter
TTChip Entwicklungs-GesmbH

                    "To get control over people, make them trust you.
                                            To make people trust you
                      don't try to tell them the truth about history
                 but make happen what you told them about the future."

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