From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,115cdbb394b3e615
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!news.glorb.com!news.cs.univ-paris8.fr!newsfeed.vmunix.org!newsfeed.stueberl.de!newsr1.ipcore.viaginterkom.de!news-peer1!btnet-feed5!btnet!news.btopenworld.com!not-for-mail
From: Martin Dowie <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Why can't you create a out of order subtype?
Date: Wed, 2 Feb 2005 19:35:22 +0000 (UTC)
Organization: BT Openworld
Message-ID: <ctra1p$nnl$1@titan.btinternet.com>
References: <1107301914.648240.237290@g14g2000cwa.googlegroups.com>
	<h5VLd.4199$cl1.3735@newsread3.news.pas.earthlink.net>
 <mailman.114.1107367326.527.comp.lang.ada@ada-france.org>
NNTP-Posting-Host: host81-154-188-69.range81-154.btcentralplus.com
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: titan.btinternet.com 1107372922 24309 81.154.188.69 (2 Feb 2005
 19:35:22 GMT)
X-Complaints-To: news-complaints@lists.btinternet.com
NNTP-Posting-Date: Wed, 2 Feb 2005 19:35:22 +0000 (UTC)
In-Reply-To: <mailman.114.1107367326.527.comp.lang.ada@ada-france.org>
X-Accept-Language: en-us, en
User-Agent: Mozilla Thunderbird 1.0RC1 (Windows/20041201)
Xref: g2news1.google.com comp.lang.ada:8136
Date: 2005-02-02T19:35:22+00:00
List-Id: <comp.lang.ada>

Marius Amado Alves wrote:
>> ...
>>
>>> 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;

That's very, very, very slow...

Cheers

-- Martin