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: 103376,85d5a13738392342
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news3.google.com!proxad.net!feeder1-2.proxad.net!news.mixmin.net!news.tornevall.net!.POSTED!not-for-mail
From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Unknown discriminants with nested records
Date: Thu, 16 Jun 2011 23:03:37 -0700
Organization: TornevallNET - http://news.tornevall.net
Message-ID: <itethj$qif$1@tornado.tornevall.net>
References: <1e197c14-a2ff-4867-85be-fda06a10e37b@a7g2000vby.googlegroups.com>
 <e3d8de4a-b442-4494-abef-4fe6c3eb7094@r27g2000prr.googlegroups.com>
NNTP-Posting-Host: 2eb76716e28f6de8f03a7dbcc9420d80
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: b51e870bd87f3aaa03f3899eeb8ef7ba
X-Complaints-To: abuse@tornevall.net
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US;
 rv:1.9.2.17) Gecko/20110424 Thunderbird/3.1.10
X-Complaints-Language: Spoken language is english or swedish - NOT ITALIAN,
 FRENCH, GERMAN OR ANY OTHER LANGUAGE!
In-Reply-To: 
 <e3d8de4a-b442-4494-abef-4fe6c3eb7094@r27g2000prr.googlegroups.com>
X-UserIDNumber: 1738
X-Validate-Post: 
 http://news.tornevall.net/validate.php?trace=b51e870bd87f3aaa03f3899eeb8ef7ba
X-Complaints-Italiano: Non abbiamo padronanza della lingua italiana - se
 mandate una email scrivete solo in Inglese, grazie
X-Posting-User: 0243687135df8c4b260dd4a9a93c79bd
Xref: g2news2.google.com comp.lang.ada:20876
Date: 2011-06-16T23:03:37-07:00
List-Id: <comp.lang.ada>

On 06/16/2011 05:39 PM, Adam Beneschan wrote:
>
> The (<>) was intended to define types with unknown discriminants;

I thought it was initially created to fix the problem with generics, where in 
Ada 83 you could have

generic -- G
    type T is limited private;
    ...
package G is
    ...
end G;

package body G is
    ...
    V : T;
    ...
end G;

package I is new G (T => String, ...);

and it wasn't caught when you would like it. In Ada 95 and later, you have to 
have (<>) on the formal to have an indefinite actual, and the generic cannot 
have an uninitialized object of the type; without (<>), the actual must be 
definite; and the problem is caught when compiling the instantiation.

-- 
Jeff Carter
"Many times we're given rhymes that are quite unsingable."
Monty Python and the Holy Grail
57