From: Stephen Leake <stephen_leake@stephe-leake.org>
Subject: Re: Silly and stupid post-condition or not ?
Date: Thu, 02 Feb 2012 04:40:20 -0500
Date: 2012-02-02T04:40:20-05:00 [thread overview]
Message-ID: <82k445fu9n.fsf@stephe-leake.org> (raw)
In-Reply-To: 5af407fc-2868-44ca-84d2-c51a2a64104d@o4g2000pbc.googlegroups.com
Adam Beneschan <adam@irvine.com> writes:
> On Feb 1, 12:36 am, Stephen Leake <stephen_le...@stephe-leake.org>
> wrote:
>> "Yannick Duchêne (Hibou57)" <yannick_duch...@yahoo.fr> writes:
>>
>>
>>
>>
>>
>> > type Parsed_Type (Status : Parsed_Status_Type) is record
>> > case Status is
>> > when Parsed =>
>> > Instance : Instance_Type;
>> > when Format_Error =>
>> > null;
>> > end case;
>> > end record; -- Parsed_Type
>>
>> > function Parsed (S : String) return Parsed_Type
>> > with Post =>
>> > (if S'Length not in Image_Length_Type then
>> > Parsed'Result.Status = Format_Error);
>> > -- There may be other failure conditions.
>>
>> > Is such a post-condition a good or bad practice in your humble or
>> > authoritative opinion ?
>>
>> > Keep in mind there may be many other cases where "Parsed'Result.Status
>> > = Format_Error" could be True; the one in the Post is not the only
>> > possible one.
>>
>> That means the post condition is misleading, and therefore bad.
>
> I don't see this. It would be misleading to someone who doesn't
> understand the fallacy of the converse, but I'd hope that computer
> science students would be taught not to make this mistake by the end
> of the first or second year.
It is true that this post condition leaves open the possibility of other
causes of failure. But they should be documented as well; why is only
this one singled out?
I agree with Dmitry; post conditions should be _complete_. If the Ada
post condition language is not strong enough to be complete, don't use
it; use natural language comments.
--
-- Stephe
next prev parent reply other threads:[~2012-02-02 9:40 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-30 23:11 Silly and stupid post‑condition or not ? Yannick Duchêne (Hibou57)
2012-01-31 6:47 ` J-P. Rosen
2012-01-31 18:48 ` Jeffrey Carter
2012-01-31 22:02 ` Yannick Duchêne (Hibou57)
2012-01-31 8:54 ` Dmitry A. Kazakov
2012-01-31 9:35 ` Georg Bauhaus
2012-01-31 10:22 ` Dmitry A. Kazakov
2012-01-31 12:33 ` Georg Bauhaus
2012-01-31 13:52 ` Dmitry A. Kazakov
2012-01-31 15:34 ` Georg Bauhaus
2012-01-31 16:24 ` Dmitry A. Kazakov
2012-01-31 19:44 ` Georg Bauhaus
2012-02-01 8:41 ` Dmitry A. Kazakov
2012-02-01 10:37 ` stefan-lucks
2012-02-01 10:51 ` Yannick Duchêne (Hibou57)
2012-02-01 13:49 ` Yannick Duchêne (Hibou57)
2012-02-01 13:49 ` Dmitry A. Kazakov
2012-02-01 16:37 ` stefan-lucks
2012-02-02 1:50 ` Silly and stupid post�?'condition " Randy Brukardt
2012-02-02 1:56 ` Silly and stupid postâ?'condition or not ? Yannick Duchêne (Hibou57)
2012-02-03 2:45 ` Silly and stupid post�?'condition or not ? Randy Brukardt
2012-02-02 8:25 ` Silly and stupid post‑condition " Dmitry A. Kazakov
2012-02-02 9:01 ` stefan-lucks
2012-02-02 9:18 ` stefan-lucks
2012-02-02 10:04 ` Dmitry A. Kazakov
2012-01-31 22:08 ` Yannick Duchêne (Hibou57)
2012-01-31 17:28 ` Dmitry A. Kazakov
2012-01-31 22:12 ` Yannick Duchêne (Hibou57)
2012-02-01 8:49 ` Dmitry A. Kazakov
2012-02-01 8:36 ` Stephen Leake
2012-02-01 16:30 ` Silly and stupid post-condition " Adam Beneschan
2012-02-02 9:40 ` Stephen Leake [this message]
2012-02-02 13:20 ` Georg Bauhaus
2012-02-02 13:35 ` Yannick Duchêne (Hibou57)
2012-02-03 3:13 ` Randy Brukardt
2012-02-03 3:33 ` Yannick Duchêne (Hibou57)
2012-02-03 8:12 ` Simon Wright
2012-02-07 2:29 ` BrianG
2012-02-07 10:43 ` Simon Wright
2012-02-08 2:25 ` BrianG
2012-02-07 21:15 ` Robert A Duff
2012-02-03 9:11 ` Dmitry A. Kazakov
2012-02-04 3:27 ` Randy Brukardt
2012-02-04 10:15 ` Dmitry A. Kazakov
2012-02-03 12:25 ` Phil Thornley
2012-02-04 9:30 ` Phil Thornley
2012-02-04 12:02 ` Phil Thornley
2012-02-05 6:18 ` Randy Brukardt
2012-02-05 10:23 ` Phil Thornley
2012-02-05 10:55 ` Yannick Duchêne (Hibou57)
2012-02-05 15:03 ` Robert A Duff
2012-02-05 18:04 ` Phil Thornley
2012-02-05 21:27 ` Robert A Duff
2012-02-05 23:09 ` Phil Thornley
2012-02-07 2:05 ` Randy Brukardt
2012-02-07 9:38 ` Dmitry A. Kazakov
2012-02-05 11:31 ` Yannick Duchêne (Hibou57)
2012-02-05 14:50 ` Robert A Duff
2012-02-07 2:11 ` Randy Brukardt
2012-02-07 2:34 ` BrianG
2012-02-07 4:38 ` Yannick Duchêne (Hibou57)
2012-02-09 3:10 ` Randy Brukardt
2012-02-04 23:07 ` Stephen Leake
2012-02-05 2:49 ` Yannick Duchêne (Hibou57)
2012-02-05 6:29 ` Randy Brukardt
2012-02-05 11:40 ` Yannick Duchêne (Hibou57)
2012-02-07 1:36 ` Randy Brukardt
2012-02-05 15:16 ` Robert A Duff
2012-02-06 4:56 ` Yannick Duchêne (Hibou57)
2012-02-06 14:39 ` Robert A Duff
2012-02-06 16:12 ` Yannick Duchêne (Hibou57)
2012-02-07 1:46 ` Randy Brukardt
2012-02-07 17:24 ` Robert A Duff
2012-02-03 6:26 ` J-P. Rosen
2012-02-03 9:12 ` Dmitry A. Kazakov
2012-02-03 9:48 ` Yannick Duchêne (Hibou57)
2012-02-03 11:09 ` Dmitry A. Kazakov
2012-02-03 11:40 ` Yannick Duchêne (Hibou57)
2012-02-03 13:18 ` Dmitry A. Kazakov
2012-02-03 14:14 ` Yannick Duchêne (Hibou57)
2012-02-03 14:45 ` Dmitry A. Kazakov
2012-02-04 3:16 ` Randy Brukardt
2012-02-04 6:27 ` Yannick Duchêne (Hibou57)
2012-02-04 10:47 ` Dmitry A. Kazakov
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