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From: Nick Roberts <nick.roberts@acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Need Value of enum type not position.
Date: Sat, 08 Nov 2003 00:16:42 +0000
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Date: 2003-11-08T00:16:42+00:00
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A possible alternative approach, not necessarily any better than using 
Unchecked_Conversion, is to use a constant lookup array:

    type Hov_Mode_Type is
          (INVALID,
           OFF,
           INITIATE,
           AUTO);

    Hov_Mode_Code: constant array (Hov_Mode_Type) of Integer :=
          (INVALID  => 7,
           OFF      => 8,
           INITIATE => 9,
           AUTO     => 10);

Depending on other factors (you have not mentioned), it may or may not be 
necessary for you to also have the enumeration representation clause.

One advantage of this technique is that it may make the logic of a certain 
part of your code immune to changes in representation (encoding) which 
might perhaps be required during the maintenance or update of another part 
of your code (or hardware). Obviously, this separation could turn out to be 
a disadvantage, depending on the logic of your code.

A disadvantage is that the lookup array is likely (but not certain) to be 
implemented as an actual array in memory. If the speed of obtaining a code 
is critical, this might matter (but I think it's unlikely). This sort of 
array can have cache-clobbering properties, which can be unfortunate from a 
speed point of view (but not in any other way).

-- 
Nick Roberts