Re: [vhdl-200x] Modular types

> Thanks Tristan - I noticed this behaviour but forgot to comment on
> it.  For other interested parties, the relevant bit of the LRM is:

[...]

> Now, I can see the reasoning - without an explicit type-conversion
> (using 'mod), it's more in the VHDL-like "fail as early as possible"
> mindset.  But perhaps without an explicit type-conversion you
> shouldn't be allowed to assign an integer to a modular type, so it
> should fail at compile-time?

Ada is strongly typed as VHDL, so you cannot assign a signed integer
to a modular integer without an explicit type-conversion.  So indeed,
such direct assignment is rejected at compile time.

> I imagine you've written rather more Ada code than I have, so could
> you elucidate a bit more on the problems the current Ada Behaviour
> causes please?  You mention it is "error-prone".  What would your
> preferred behaviour be - to fail at compile-time, or treat all
> assignments as asking for a "wraparound", or something else
> entirely?

The issue is the behaviour of the type-conversion.  When you use modular
type (in Ada), you think that all operations wraps-around.  That's true
except for type conversion.  If M is a modular type, M (Integer'(-1))
raise an error instead of returning M'Modulus - 1.  I think this was
a mistake (and I am not alone, see AI-00340 for opinions).

Regards,
Tristan.

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