From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada2012 Invariants and obaque types
Date: Tue, 21 Jun 2011 20:53:17 +0200
Date: 2011-06-21T20:53:17+02:00 [thread overview]
Message-ID: <1rxmqjvvd0nk6.1pqiavml8xwzf.dlg@40tude.net> (raw)
In-Reply-To: op.vxfvc6uxule2fv@douda-yannick
On Tue, 21 Jun 2011 20:37:44 +0200, Yannick Duch�ne (Hibou57) wrote:
> Le Tue, 21 Jun 2011 14:08:15 +0200, Dmitry A. Kazakov
> <mailbox@dmitry-kazakov.de> a �crit:
>
>> On Tue, 21 Jun 2011 01:53:31 -0700 (PDT), Martin wrote:
>>
>>> package P1 is
>>> type T1 is tagged private
>>> with Invariant => Is_Valid (T1);
>>
>> Unrelated to Ada, but in theory, an invariant is a private implementation
>> dependent thing. An invariant is trivially true in all public views of
>> the object,
> I understand the point and had the same first feeling too.
The first feeling is always the right one. (:-))
> While that's OK
> in theory, in practice the user may wish methods to check for validity
> rules defined for a type.
Validity is a misconception. In a properly typed language any value is
valid, that is the property of being typed. A value is invalid when the
type system was circumvented, which should never happen publicly.
> Then, Is_Valid is abstract enough. And
> after-all, you already have 'Valid attribute in Ada. This is useful for
> designs relying on defensive programming and which disallow use of
> exceptions.
'Valid is a hack around missing value initialization enforcement or some
kludges to support Unchecked_Conversion. It cannot justify anything because
'Valid itself lacks credibility.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2011-06-21 18:53 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-21 8:53 Ada2012 Invariants and obaque types Martin
2011-06-21 10:27 ` Yannick Duchêne (Hibou57)
2011-06-21 10:36 ` Martin
2011-06-21 10:46 ` Martin
2011-06-21 18:42 ` Yannick Duchêne (Hibou57)
2011-06-21 10:43 ` Ludovic Brenta
2011-06-21 10:53 ` Martin
2011-06-21 11:14 ` Martin
2011-06-21 11:31 ` Robert A Duff
2011-06-21 11:48 ` Martin
2011-06-21 12:01 ` Martin
2011-06-21 12:13 ` Robert A Duff
2011-06-21 12:22 ` Martin
2011-06-21 12:54 ` Robert A Duff
2011-06-21 13:00 ` Martin
2011-06-21 12:08 ` Dmitry A. Kazakov
2011-06-21 12:17 ` Georg Bauhaus
2011-06-21 12:31 ` Dmitry A. Kazakov
2011-06-21 13:29 ` Georg Bauhaus
2011-06-21 14:42 ` Dmitry A. Kazakov
2011-06-21 18:37 ` Yannick Duchêne (Hibou57)
2011-06-21 18:53 ` Dmitry A. Kazakov [this message]
2011-06-21 19:34 ` Vinzent Hoefler
2011-06-21 20:52 ` Dmitry A. Kazakov
2011-06-21 21:50 ` Vinzent Hoefler
2011-06-22 7:55 ` Dmitry A. Kazakov
2011-06-21 21:18 ` Manuel Collado
2011-06-22 8:00 ` Dmitry A. Kazakov
2011-06-22 10:39 ` Egil Høvik
2011-06-22 13:57 ` Martin
2011-06-23 16:21 ` anon
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