Re: Representation clause for enumeratives

[Steve O'Neill <soneill@avidyne.com>]

I'm making an assumption here that you are choosing these enumeration
values to match to some hardware encoding.  When I have found myself in
similar situations in the past I have usually taken a different route.

Rather than try to encode the enumeration values (which frequently leads to
frustration and maintenance issues) I would instead create an array of
appropriately typed objects that are indexed by the enumeration that I was
trying to map.  I would index into, search through, etc. that array
whenever I wanted to convert to/from the external hardware to the internal
meaning.  It might not seem as elegant or as potentially efficient as
assigning the enumeration value directly but in my experience it is a lot
less painful.  With the proper encapsulation and design metaphor it can
actually turn out to be fairly intuitive.

Steve O'Neill

"M. Kotiaho" wrote:

> Robert Dewar wrote:
>
> > In article <95u470$ho1$1@nnrp1.deja.com>,
> >   Sandro Binetti <sandrobinetti@my-deja.com> wrote:
> > > In article <95tre2$f33@news.kvaerner.com>,
> > >   "Tarjei T. Jensen" <tarjei.jensen@kvaerner.com> wrote:
> > > > Have you tried to insert a size directive. e.g
> > > >
> > > > type TYP_ENUM is (A,B,C);
> > > >
> > > > for TYP_ENUM'size use 32;
> > >
> > > Done. But the problem is still the same ...
> > > Why?
> >
> > Presumably a capacity limitation in the compiler you are
> > using, not a terribly justifiable one, so you should bring
> > this to the attention of the vendor. Most likely the decision
> > is to use a signed 32-bit integer to represent enumerations,
> > which as you see in this case can be an annoying restriction.
> >
> > Sent via Deja.com
> > http://www.deja.com/
>
> Indeed, GNAT on WinNT (Pentium-II) will allow the following:
>
>     type TYP_ENUM is (A,B,C);
>
>     for TYP_ENUM use(
>        -16#8000000000000000#,
>         16#00000002#,------#
>         16#7FFFFFFFFFFFFFFF#  -- <<<<< NOTICE THIS VALUE !!!
>  );
>
> Apparently, GNAT is using a signed 64-bit integer.
>
> Incidently, both compilers are sticking to the
> "at least" portion of the implementation advice -- they
> just define System.Min_Int and System.Max_Int differently:
>
> (Copied from Lutz Donnerhacke's post)
> >Implementation Advice
> > 9. The recommended level of support for
> enumeration_representation_clauses is:
> >      1. An implementation should support at least the internal codes
> in the
> >         range System.Min_Int..System.Max_Int. An implementation need
> not
> >         support enumeration_representation_clauses for boolean types.
>
> Markku Kotiaho