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From: Jacob Sparre Andersen <sparre@nbi.dk>
Newsgroups: comp.lang.ada
Subject: Re: accesing internal codes used for an enumeration
Date: Mon, 07 May 2001 17:33:02 +0200
Organization: Centre for Chaos and Turbulence Studies, Niels Bohr Institute
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Date: 2001-05-07T17:33:02+02:00
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Marius:

> Implementation:
> 
>   type Names is (Ping, Pong);
>   for Names use (Ping => 123, Pong => 456);
> 
> I found out the hardway that attribute Pos does not return the internal
> code.

It can be read from the LRM, although I think it could be formulated
a bit clearer.

> The ARM says this at 13.4(11), and tells you to use
> Unchecked_Conversion instead--but does not instruct you on the types of
> the conversion.  Where might one learn that?  Thanks.

You should declare an integer type that is suitable for the mapping.
An idea for the implementation:

   for Names'Size use 16;

   type Name_Indices is range 0 .. 2**16 - 1;
   for Name_Indices'Size use 16;

   function To_Index (Name : Names) return Name_Indices is
     new Ada.Unchecked_Conversion (Source => Names,
                                   Target => Name_Indices);

Jacob
-- 
"... det er ul�kkert, at man selektivt vil t�mme
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 Christian Mikkelsen