From: "J-P. Rosen" <rosen@adalog.fr>
Subject: Re: Discriminants of tagged types
Date: Wed, 27 Oct 2010 15:54:17 +0200
Date: 2010-10-27T15:54:17+02:00 [thread overview]
Message-ID: <ia9aub$cra$1@news.eternal-september.org> (raw)
In-Reply-To: <14314714-e92c-4036-9cbb-da8e72489261@h7g2000yqn.googlegroups.com>
Le 27/10/2010 14:16, Maciej Sobczak a �crit :
[...]
> GNAT says that discriminants of tagged types cannot have default
> values.
and it is right.
> I find it disturbing and artificial, but perhaps I don't see the big
> picture. What is the rationale for this limitation?
Default values of discriminants are not "just" default values: they
define another form of record, the polymorphic record.
Tagged types define a different kind of polymorphism, through inheritance.
Having two orthogonal kinds of polymorphism in the same data structure
would be difficult to manage, both from a design and an implementation
point of view.
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prev parent reply other threads:[~2010-10-27 13:54 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-27 12:16 Discriminants of tagged types Maciej Sobczak
2010-10-27 12:34 ` Ludovic Brenta
2010-10-27 13:19 ` Dmitry A. Kazakov
2010-10-27 13:52 ` Robert A Duff
2010-10-27 14:12 ` Dmitry A. Kazakov
2010-10-27 13:44 ` Robert A Duff
2010-10-27 15:06 ` Adam Beneschan
2010-10-27 15:58 ` Yannick Duchêne (Hibou57)
2010-10-27 16:35 ` Vinzent Hoefler
2010-10-27 17:58 ` J-P. Rosen
2010-10-27 20:18 ` Yannick Duchêne (Hibou57)
2010-10-27 20:26 ` Adam Beneschan
2010-10-27 22:07 ` Yannick Duchêne (Hibou57)
2010-10-27 22:42 ` Adam Beneschan
2010-10-27 15:13 ` Maciej Sobczak
2010-10-27 16:02 ` Yannick Duchêne (Hibou57)
2010-10-27 21:13 ` Maciej Sobczak
2010-10-27 21:23 ` Ludovic Brenta
2010-10-28 8:38 ` Maciej Sobczak
2010-10-27 21:25 ` Vinzent Hoefler
2010-10-28 7:53 ` Dmitry A. Kazakov
2010-10-28 8:50 ` Maciej Sobczak
2010-10-28 10:28 ` Dmitry A. Kazakov
2010-10-28 17:48 ` Yannick Duchêne (Hibou57)
2010-10-29 18:59 ` Vinzent Hoefler
2010-10-30 21:05 ` Maciej Sobczak
2010-10-30 21:21 ` Vinzent Hoefler
2010-10-30 22:01 ` Yannick Duchêne (Hibou57)
2010-10-31 16:20 ` Maciej Sobczak
2010-10-31 17:04 ` Yannick Duchêne (Hibou57)
2010-10-31 18:36 ` Shark8
2010-10-31 21:06 ` Maciej Sobczak
2010-11-01 0:44 ` Shark8
2010-11-01 9:41 ` Maciej Sobczak
2010-10-27 16:06 ` Robert A Duff
2010-10-27 16:34 ` Yannick Duchêne (Hibou57)
2010-10-27 21:05 ` Maciej Sobczak
2010-10-28 0:35 ` Robert A Duff
2010-10-28 8:55 ` Maciej Sobczak
2010-10-27 21:28 ` Simon Wright
2010-10-27 13:54 ` J-P. Rosen [this message]
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