From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Silly and stupid post‑condition or not ?
Date: Tue, 31 Jan 2012 09:54:03 +0100
Date: 2012-01-31T09:54:03+01:00 [thread overview]
Message-ID: <12kegkefstjiy.115bw2vmx23ll.dlg@40tude.net> (raw)
In-Reply-To: op.v8w6ptk5ule2fv@douda-yannick
On Tue, 31 Jan 2012 00:11:43 +0100, Yannick Duchêne (Hibou57) wrote:
> 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 ?
I would say it would be a bad practice. The reason is that IMO the
postcondition must be complete, it must tell all truth or nothing. Your
prostcondition is a partial truth, it does not describe all cases when
Status is mandated to be Format_Error.
Yes, it boils down to the implied semantics of the postconditions. If you
consider them mere comments occasionally breaking the program execution by
throwing exceptions at random, then your example might fit into that model.
If you rather view them as contracts, then good contracts should have no
holes.
Note that it is not necessarily about how detailed the semantics is to be
described by pre-/postconditions. I mean, there is a space between
pre-/postconditions suitable for correctness proofs and ones which don't.
You can have the latter if you wish, but still it must be complete. In your
case such a loose postcondition would actually be:
Status = Format_Error if something is wrong
If you cannot spell that using available means then don't.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2012-01-31 8:54 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 [this message]
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
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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