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,f2690a5e963b61b6
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!news.glorb.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local01.nntp.dca.giganews.com!nntp.megapath.net!news.megapath.net.POSTED!not-for-mail
NNTP-Posting-Date: Mon, 11 Jul 2005 13:35:48 -0500
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
References: <1120474891.635131.216700@g44g2000cwa.googlegroups.com>
 <1120575076.876798.108220@g44g2000cwa.googlegroups.com>
 <1120583470.429264.325450@g43g2000cwa.googlegroups.com>
 <osoo6gccqpnm.2o5eehhafwb1.dlg@40tude.net>
 <42cb8d21$0$22761$9b4e6d93@newsread2.arcor-online.net>
 <ldco4pwrxop4$.1py0a7isiagea.dlg@40tude.net>
 <z--dnRI60_7j_lHfRVn-qw@megapath.net>
 <tyi72ga8ch55$.3tea03tbwrtx.dlg@40tude.net>
 <42cd064c$0$10817$9b4e6d93@newsread4.arcor-online.net>
 <k62rlp2n1ls3.1cnwufmnuit7v.dlg@40tude.net>
 <42cda8c4$0$22780$9b4e6d93@newsread2.arcor-online.net>
 <1u3hh2597i4ne$.1ryetugksbmus.dlg@40tude.net>
 <42ce5856$0$22762$9b4e6d93@newsread2.arcor-online.net>
 <1o398w3zo2zf1$.f1f7tukylueo$.dlg@40tude.net>
 <CpednSZYNbLOHk3fRVn-jQ@megapath.net>
 <nmv39ipirsbg$.1or742g96p5km.dlg@40tude.net>
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: Mon, 11 Jul 2005 13:38:56 -0500
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 5.50.4952.2800
X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4952.2800
Message-ID: <tqSdnVlRt7mZIU_fRVn-tg@megapath.net>
NNTP-Posting-Host: 64.32.209.38
X-Trace: 
 sv3-wTswTs07NN/KdJj4NTRkuyfd5aCLeOvbA5DlO1BSEg/5S109T4t7u6A9VphWgSyRBqPjOOLfLALvbd9!ErYU36jWnHeTD/Az+92t38qq4OxUBHrZPorfoJ7VGm3Uv/Vg84lahonhT/Ur5Jq4O+qqU/yj8Vd4
X-Complaints-To: abuse@megapath.net
X-DMCA-Complaints-To: abuse@megapath.net
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint
 properly
X-Postfilter: 1.3.31
Xref: g2news1.google.com comp.lang.ada:12000
Date: 2005-07-11T13:38:56-05:00
List-Id: <comp.lang.ada>

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:nmv39ipirsbg$.1or742g96p5km.dlg@40tude.net...
> > The abstract view of iteration is that it produces *every* element of
the
> > container, and no others, in *some* unspecified order. That applies both
the
> > the passive iterator Iterate and the cursor based routines like Next.
>
> An unspecified order is still an order. What could be said about that
> unspecified order?

Nothing. That's the meaning of "unspecified"! The implementation can use any
convinient order.

> May the order vary for a constant container?

There is no such thing as a constant container. You can declare a container
object constant, but that doesn't make the container constant.

> How does it when the container gets changed?

That's irrelevant. If the container is changed, cursor iteration may fail
(passive iteration would raise Program_Error; that's part of the contract of
all of the containers).

...
> > Of course, specific containers do require a specific order, and *then*
you
> > can rely upon it. But not in a generic algorithm.
>
> A generic algorithm is just a class-wide procedure. The problem is the
> contract of the class. If iteration is in the contract, then its behavior
> must be defined. So that the correctness of the algorithm would be
> independent on any possible implementation. If it is outside, then there
> must be no [easy] way to use it.

For a passive iterator, the contract is that each element is visited exactly
once, in an unspecified order. Signficant changes to the container during a
passive iterator are *not* allowed (they raise Program_Error). Thus, the
order is irrelevant.

                     Randy.