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,fdd685ffa59d584d,start
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!postnews.google.com!r21g2000yqd.googlegroups.com!not-for-mail
From: KK6GM <mjsilva@scriptoriumdesigns.com>
Newsgroups: comp.lang.ada
Subject: What would be the Ada solution?
Date: Fri, 4 Feb 2011 08:33:57 -0800 (PST)
Organization: http://groups.google.com
Message-ID: 
 <0aa67233-4210-483b-b35c-8e872f87cb8f@r21g2000yqd.googlegroups.com>
NNTP-Posting-Host: 12.35.64.226
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
X-Trace: posting.google.com 1296837237 5825 127.0.0.1 (4 Feb 2011 16:33:57
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: Fri, 4 Feb 2011 16:33:57 +0000 (UTC)
Complaints-To: groups-abuse@google.com
Injection-Info: r21g2000yqd.googlegroups.com; posting-host=12.35.64.226;
 posting-account=qZVz2QoAAAAN9WxYp-9jYb7jORc4Zqwt
User-Agent: G2/1.0
X-HTTP-Via: 1.1 barracudaweb.tritool.rancho:8080 (http_scan/4.0.2.6.19)
X-HTTP-UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1;
 Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30;
 .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; MDDR; .NET4.0C; .NET4.0E;
 InfoPath.1),gzip(gfe)
Xref: g2news1.google.com comp.lang.ada:16868
Date: 2011-02-04T08:33:57-08:00
List-Id: <comp.lang.ada>

A colleague is working on some old code, written in C, that uses an
"out of range" integer value to indicate no valid value.  Thus, a
default value (in this case 0x7FFFFFFF) means no value has been
entered.  All code that uses any values should check for this no-value
and act accordingly, but of course not all the code actually does
that, and there are odd cases where the no-value value gets processed
as a valid value and then Bad Things Happen.

I'm curious what the Ada approach to this issue would be, the issue
being to differentiate between valid and invalid values, and to catch
(compile time or run time) any manipulation of an invalid value as if
it were a valid value.