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From: Marius Amado Alves <amado.alves@netcabo.pt>
To: comp.lang.ada@ada-france.org
Subject: Re: Why can't you create a out of order subtype?
Date: Wed, 2 Feb 2005 17:55:50 +0000
Date: 2005-02-02T17:55:50+00:00	[thread overview]
Message-ID: <mailman.114.1107367326.527.comp.lang.ada@ada-france.org> (raw)
In-Reply-To: <h5VLd.4199$cl1.3735@newsread3.news.pas.earthlink.net>

> ...
>> Another option that I think is much, much worse then the boolean array
>> would be create an overloaded type...
>> type msg is ( msg_a, msg_b, msg_c, msg_d, msg_e);
>> type vowelmsg ( msg_a, msg_e);
>> But as you know, msg.msg_e = 4 and vowelmsg.msg_e = 1 so an unchecked
>> conversion is wrong on so many levels.
>
> Yes, this may be worse, but you can at least get Unchecked_Conversion 
> to work:
>
> for Vowelmsg use (Msg_A => 0, Msg_E => 4);
> for Vowelmsg'Size use Msg'Size;
>
> This would still be a run-time check:...

For run-time I find the "Value of Image" idiom a better one. It's 
readily available. No Unchecked_Conversion required.

declare
    M : Msg := Whatever;
    V : Vowelmsg;
begin
    V := Vowelmsg'Value (Msg'Image (M));
    -- if control reaches here then M is a vowel
exception
    when Constraint_Error => -- M is not a vowel
end;




  reply	other threads:[~2005-02-02 17:55 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-02-01 23:51 Why can't you create a out of order subtype? brett_gengler
2005-02-02  0:24 ` Jeffrey Carter
2005-02-02 17:55   ` Marius Amado Alves [this message]
2005-02-02 18:50     ` Pascal Obry
2005-02-02 20:22       ` Marius Amado Alves
2005-02-03  4:36       ` Wes Groleau
2005-02-03 12:59         ` Marius Amado Alves
2005-02-04  3:42           ` Wes Groleau
2005-02-02 19:35     ` Martin Dowie
2005-02-02 20:35       ` Marius Amado Alves
2005-02-02 21:18         ` Martin Dowie
2005-02-03 19:40       ` Robert A Duff
2005-02-03 20:22         ` Marius Amado Alves
2005-02-03 22:05           ` Robert A Duff
2005-02-04  6:49           ` Martin Dowie
2005-02-02 22:26 ` Georg Bauhaus
2005-02-03 23:09 ` Robert A Duff
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