Re: enumration using integers?

["Marc A. Criley" <mcqada@earthlink.net>]

Sven Nilsson wrote:
> 
> Hello
> 
> I have a little problem that I don't want to spend time solving...
> 
> If I want to make an enumerated type using integers, like:
> 
>    type Distance is (10, 20, 30, 40, 50);
> 
> The compiler will complain about missing identifiers. How do I get the
> blasted machine to understand that the integers are the identifiers I
> want?
> 

Well, integers are not identifiers, and enumeration literals must be
identifiers, so you cannot create an enumeration type whose literals are
integers.

Given a type definition like:

   type Distance is (Km_10, Km_20, Km_30, Km_40, Km_50);

If you're using values of that type in registers or particular memory
locations, as is commonly done in embedded programming, you can
associate a representation specification with the type:

   for Distance use (Km_10 => 10, Km_20 => 20, Km_30 => 30,
                     Km_40 => 40, Km_50 => 50);

Or you can just use a little lookup table to get the value:

   type Distance_Values is array (Distance) of Natural;

   Dist : constant Distance_Values :=
                  (Km_10 => 10, Km_20 => 20, Km_30 => 30,
                   Km_40 => 40, Km_50 => 50);

Then just look up the value through the table:

   for D in Distance'Range loop
      Process(Dist(D));
   end loop;


Marc A. Criley
Senior Staff Engineer
Quadrus Corporation
www.quadruscorp.com