From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: discriminant questions
Date: Sat, 24 Sep 2011 08:56:35 +0200
Date: 2011-09-24T08:56:35+02:00 [thread overview]
Message-ID: <19iim6m72b6s4$.qe1pwkufdkzn$.dlg@40tude.net> (raw)
In-Reply-To: j5j212$t53$1@munin.nbi.dk
On Fri, 23 Sep 2011 17:42:39 -0500, Randy Brukardt wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:xumuqaannoov$.18le1ojsi30l8.dlg@40tude.net...
>> On Fri, 23 Sep 2011 05:23:38 -0400, Stephen Leake wrote:
>>
>>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>>>
>>>> Consider a generic
>>>> implementation of removing all elements of the container using
>>>> iterators:
>>>>
>>>> This := Container.First;
>>>> while This /= Null_Iterator loop
>>>> Next := This.Next;
>>>> This.Delete;
>>>> This := Next;
>>>> end loop;
>>>>
>>>> This may work or not depending on the semantics of Delete. E.g. for a
>>>> circular list, it will loop forever.
>>>
>>> No, it will produce an invalid dereference; for a one element circular
>>> list, This.Next = This, so Next is invalid after This.Delete.
>>
>> If the element is only in this list and freed upon delete, then Next is
>> dangling.
>>
>> However a common schema is that elements of lists are actually never freed,
>> but rather moved to the list of unused element to reuse, when a new element
>> is needed. For this implementation the above loops.
>
> In that case, the implementation of cursors is broken (IMHO) - dangling
> cursor detection should have been manditory, and surely should be in the
> case of element reuse. So Program_Error should be raised in either case,
> nothing erroneous or looping here.
Which does not invalidate my point about difficulties of generic
programming with iterators, because the semantics of operations on
iterators is ill defined. Whether accessing the iterator Next raised
Program_Error or looped is no matter, so long it applies to a concrete
container implementation.
For generic programming you need Delete working in the same (specified) way
for all container types of the set. Its effect on all iterators must be
defined and same. My point and the purpose of the example was that this is
extremely difficult to achieve, if possible.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2011-09-24 6:56 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-17 16:30 discriminant questions ytomino
2011-09-17 17:19 ` Dmitry A. Kazakov
2011-09-17 17:46 ` ytomino
2011-09-17 19:41 ` Dmitry A. Kazakov
2011-09-17 22:55 ` ytomino
2011-09-18 8:50 ` Dmitry A. Kazakov
2011-09-18 10:54 ` ytomino
2011-09-18 11:35 ` Dmitry A. Kazakov
2011-09-18 12:41 ` ytomino
2011-09-18 13:17 ` Dmitry A. Kazakov
2011-09-18 16:22 ` ytomino
2011-09-18 16:32 ` ytomino
2011-09-18 18:15 ` Dmitry A. Kazakov
2011-09-18 23:44 ` ytomino
2011-09-19 7:27 ` Dmitry A. Kazakov
2011-09-18 14:43 ` Dmitry A. Kazakov
2011-09-18 16:46 ` Robert A Duff
2011-09-18 18:01 ` Dmitry A. Kazakov
2011-09-18 19:20 ` Maciej Sobczak
2011-09-19 7:39 ` Dmitry A. Kazakov
2011-09-19 20:00 ` Maciej Sobczak
2011-09-20 7:33 ` Dmitry A. Kazakov
2011-09-20 15:45 ` Maciej Sobczak
2011-09-20 16:48 ` Dmitry A. Kazakov
2011-09-20 20:19 ` Maciej Sobczak
2011-09-21 7:48 ` Dmitry A. Kazakov
2011-09-21 20:51 ` Maciej Sobczak
2011-09-22 8:07 ` Dmitry A. Kazakov
2011-09-22 20:57 ` Maciej Sobczak
2011-09-23 7:59 ` Dmitry A. Kazakov
2011-09-23 10:57 ` Georg Bauhaus
2011-09-23 22:30 ` Randy Brukardt
2011-09-23 22:50 ` Randy Brukardt
2011-09-24 6:46 ` Dmitry A. Kazakov
2011-09-26 22:48 ` Randy Brukardt
2011-09-27 8:10 ` Dmitry A. Kazakov
2011-09-27 10:18 ` Georg Bauhaus
2011-09-27 12:14 ` Dmitry A. Kazakov
2011-09-27 15:11 ` Georg Bauhaus
2011-09-27 15:38 ` Dmitry A. Kazakov
2011-09-27 18:06 ` Georg Bauhaus
2011-09-27 19:06 ` Dmitry A. Kazakov
2011-09-29 0:01 ` Georg Bauhaus
2011-09-29 8:26 ` Dmitry A. Kazakov
2011-09-30 1:24 ` Randy Brukardt
2011-09-30 8:10 ` Dmitry A. Kazakov
2011-09-30 10:07 ` Georg Bauhaus
2011-09-30 12:38 ` Dmitry A. Kazakov
2011-09-30 17:40 ` Georg Bauhaus
2011-09-30 18:55 ` Dmitry A. Kazakov
2011-09-23 9:23 ` Stephen Leake
2011-09-23 9:48 ` Dmitry A. Kazakov
2011-09-23 22:42 ` Randy Brukardt
2011-09-24 6:56 ` Dmitry A. Kazakov [this message]
2011-09-26 22:43 ` Randy Brukardt
2011-09-24 10:47 ` Stephen Leake
2011-09-24 12:54 ` Simon Wright
2011-09-24 14:46 ` Dmitry A. Kazakov
2011-09-24 16:21 ` Simon Wright
2011-09-24 16:43 ` Dmitry A. Kazakov
2011-09-22 2:52 ` Randy Brukardt
2011-09-22 8:11 ` Dmitry A. Kazakov
2011-09-20 0:01 ` Randy Brukardt
2011-09-20 7:38 ` Dmitry A. Kazakov
2011-09-20 11:11 ` AdaMagica
2011-09-20 12:09 ` Dmitry A. Kazakov
2011-09-20 12:31 ` AdaMagica
2011-09-20 12:57 ` Dmitry A. Kazakov
2011-09-20 23:28 ` ytomino
2011-09-21 5:03 ` AdaMagica
2011-09-21 8:08 ` Dmitry A. Kazakov
2011-09-21 10:03 ` Georg Bauhaus
2011-09-21 10:29 ` Dmitry A. Kazakov
2011-09-22 3:21 ` Randy Brukardt
2011-09-22 3:05 ` Randy Brukardt
2011-09-19 23:35 ` Randy Brukardt
2011-09-20 21:39 ` ytomino
2011-09-22 3:32 ` Randy Brukardt
2011-09-18 16:32 ` ytomino
2011-09-19 14:46 ` ytomino
2011-09-19 15:14 ` Dmitry A. Kazakov
2011-09-19 17:49 ` ytomino
2011-09-20 7:29 ` Georg Bauhaus
2011-09-20 19:50 ` ytomino
2011-09-20 8:08 ` Dmitry A. Kazakov
2011-09-20 18:47 ` ytomino
2011-09-21 8:16 ` Dmitry A. Kazakov
2011-09-21 9:55 ` ytomino
2011-09-22 3:26 ` Randy Brukardt
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