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From: Wojtek Narczynski <wojtek@power.com.pl>
Newsgroups: comp.lang.ada
Subject: Enumeration representation enhancement proposal
Date: Thu, 14 Oct 2004 11:31:38 +0200
Organization: tp.internet - http://www.tpi.pl/
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Date: 2004-10-14T11:31:38+02:00
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Hello,

Enumeration representation in their current form are not very useful,
because there is no treatment of invalid values. That's why constants, and
constant to enum mapping arrays are used so heavily in real interfacing
code.

Invalid external values are rather norm than exception, thus they deserve
'non-exceptional' treatment. The 'Valid attribute alleviates the problem,
but it is not very convenient, for example won't work in case statements,
it requires to have two different ways to log the value (valid and invalid).

Maybe this could be improved in Ada 2005? For example:


type Mix_Code is (Red, Green, Blue, Grey);

--  Modest proposal

for Mix_Code use (Red => 1, Green => 2, Blue => 3, Grey => others);

This should be relatively straightforward to implement, and would cover
most needs.

However...

--  Die-hard proposal

for Mix_Code use
  (Red => 1 | 10, Green => 11 .. 20, Blue => 21 .. 30 | 40, Grey => others);


An unambiguous mapping from the rep value to Ada enum would be required,
not the other direction.

Regards,
Wojtek