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=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!news.stack.nl!reality.xs3.de!news.jacob-sparre.dk!loke.jacob-sparre.dk!pnx.dk!.POSTED!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Your wish list for Ada 202X
Date: Mon, 14 Apr 2014 18:39:24 -0500
Organization: Jacob Sparre Andersen Research & Innovation
Message-ID: <lihrjd$pqv$1@loke.gir.dk>
References: <7f1c01c5-3563-4b94-9831-152dbbf2ecdc@googlegroups.com>
 <tvtYu.83108$tD4.27538@fx25.iad> <lgve1q$b56$1@loke.gir.dk>
 <x9RYu.3020$XJ3.767@fx09.iad> <lh26es$3gg$1@loke.gir.dk>
 <o4o5ao9k7hz9.l7ebk8qxfv32.dlg@40tude.net> <lh4pfe$vrn$1@loke.gir.dk>
 <8bhozh836pyt$.1qctlysud0s2q$.dlg@40tude.net> <lhcv8r$iol$1@loke.gir.dk>
 <1cdsyxjzsfgzm.1synpaujysv21$.dlg@40tude.net> <lhi3ia$bos$1@loke.gir.dk>
 <1aa804jg9qq4o$.wdiq33yo621l.dlg@40tude.net> <lhviiu$q77$1@loke.gir.dk>
 <yl8s1sbhw0lw.1bhypcrvreord.dlg@40tude.net> <li217v$uvk$1@loke.gir.dk>
 <1w6eh0aiksmdh$.1h16p7y0b8c6h.dlg@40tude.net> <li5354$c8e$1@loke.gir.dk>
 <17twpp4p8u7o$.1idvzaaio4f3t$.dlg@40tude.net> <li76jb$bnj$1@loke.gir.dk>
 <16388p09ph28u$.1mglp0rm7pli9$.dlg@40tude.net> <li9nne$1mf$1@loke.gir.dk>
 <9cm2e094hvj7.sj0t2sh2komn.dlg@40tude.net>
NNTP-Posting-Host: static-69-95-181-76.mad.choiceone.net
X-Trace: loke.gir.dk 1397518766 26463 69.95.181.76 (14 Apr 2014 23:39:26 GMT)
X-Complaints-To: news@jacob-sparre.dk
NNTP-Posting-Date: Mon, 14 Apr 2014 23:39:26 +0000 (UTC)
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
X-RFC2646: Format=Flowed; Original
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157
Xref: news.eternal-september.org comp.lang.ada:19300
Date: 2014-04-14T18:39:24-05:00
List-Id: <comp.lang.ada>

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:9cm2e094hvj7.sj0t2sh2komn.dlg@40tude.net...
> On Fri, 11 Apr 2014 16:44:13 -0500, Randy Brukardt wrote:
>
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>> news:16388p09ph28u$.1mglp0rm7pli9$.dlg@40tude.net...
>
>>> Your example refers to overloading possible for operations on unrelated
>>> types. I don't see how this is scenario could be possible for a 
>>> primitive
>>> MD operation. One of the requirements put on MD is that *all* 
>>> combinations
>>> of tags up to the root of the inheritance tree be defined and checked at
>>> compile time. This requirement automatically precludes appearance of C 
>>> from
>>> air. It cannot be primitive and thus the preference rules would not 
>>> apply
>>> to it.
>>
>> Doesn't matter. First, you'd have to prevent adding or removing new
>> primitive operations to a hierarchy. That seems like a nasty limitation.
>
> What? This limitation is with us since Ada 95! You cannot add a primitive
> operation after the freezing point in Ada. You cannot remove a primitive
> operation at all.

This is an issue with program maintenance, not with an unchanging 
declaration -- so freezing is completely irrelevant. If someone decides 
there is a need to add a primitive operation to the root (for instance), 
then a preference rule towrd the root could potentially silently change the 
behavior of a otherwise tested/proved program. That's the sort of thing that 
needs to be prevented, lest maintenance become too dangerous to allow in 
existing systems.

                                           Randy.