RE: [vhdl-200x] Corrections to Minutes for VHDL-200X-FT meeting, San Jose Dec...

Subject: RE: [vhdl-200x] Corrections to Minutes for VHDL-200X-FT meeting, San Jose Dec...
From: Marcus Harnisch (
Date: Fri Dec 12 2003 - 12:06:43 PST

Hi Stephen,

Giving it a second or third thought, implicit boolean equivalence
might not be that evil.

From a pure user's perspective (leaving aside detailed knowledge about
language mechanisms for a moment), we do a lot of what very close to
implicit type conversion already. We just call it overloading.

given the declaration:

    unsigned u1, u2;

what I enjoy is being able to type is:

    u2 <= u1 + 1; -- or '1' for std_logic

, where the integer literal `1' is (from a user's perspective)
implicitly converted to an unsigned value.

So having an implicit conversion to boolean in certain well-defined
places might not be such a bad idea. And, as you pointed out, nobody
has to use it. I am not yet decided whether I will or not.

As far as (unintentional) misuse is concerned, I cannot think of a
particular example where that would be possible using the mechanism
you suggested. Has anyone else thought about potential issues?

In particular we won't be able to see things like the famous C-blunder

   if (a = b) { /* should that have been `==' ? */

What I think most VHDL users require is that the language remains easy
to read (and write) and that a Lint tool does not become a mandatory
investment (it is for The Other HDL). We want VHDL compilers to be
able to point us to subtle errors every one of us makes in daily life,
before we run a simulation.

IMHO, the most important thing for everyone who was not at the meeting
to judge (if only I could...), is a detailed version of the last slide
in the presentation Jim posted. Where can I find one?

Best regards,


Bailey, Stephen writes:
> If this were a huge problem, Verilog users would be complaining
> about it. They are not.

I hardly consider this a convincing argument, but still.

Marcus Harnisch               | Mint Technology, a division of LSI Logic | 200 West Street, Waltham, MA 02431
Tel: +1-781-768-0772          |

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