From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: tagged record child: override constructor?
Date: Tue, 13 Sep 2005 09:32:58 +0200
Date: 2005-09-13T09:32:54+02:00 [thread overview]
Message-ID: <1uri5gd2n7om0.1ujkzb26ayxdx.dlg@40tude.net> (raw)
In-Reply-To: 1126591134.797303.318920@z14g2000cwz.googlegroups.com
On 12 Sep 2005 22:58:54 -0700, sean.gilbertson@gmail.com wrote:
> I have a tagged record that is declared private, along with a
> constructor function which returns an instance. I do this to enforce
> the assignment of several required fields in the record, so if you know
> how to do this another way, please let me know!
Ada.Finalization?
> But Ada is telling me I have to override this function in the child.
I presume you have something like:
type X is private;
function Create (...) return X;
private
type X is tagged ...;
> This doesn't make a lot of sense.
On the contrary, Create above is covariant, that means that a derived type
cannot inherit it, because otherwise the result would be of the parent type
X. Thus it has to be overridden in each derived type. This is a very
important feature that saves a lot of debugging.
> How can I deal with this?
Just make Create contravariant, provided that you know how to create
derived instances from there. In Ada contravariant subroutines are
class-wide:
type X is tagged private;
-- Publicly tagged to have an ability to declare class-wides
function Create (...) return X'Class;
-- This is same for all derived types
private
type X is tagged ...;
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2005-09-13 7:32 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-13 5:58 tagged record child: override constructor? sean.gilbertson
2005-09-13 6:39 ` David Trudgett
2005-09-13 7:32 ` Dmitry A. Kazakov [this message]
2005-09-13 7:56 ` tmoran
2005-09-13 15:23 ` sean.gilbertson
2005-09-13 17:37 ` Martin Krischik
2005-09-13 19:29 ` Ludovic Brenta
2005-09-14 7:49 ` Dmitry A. Kazakov
2005-09-14 9:05 ` Maciej Sobczak
2005-09-14 13:20 ` Dmitry A. Kazakov
2005-09-14 13:52 ` Hyman Rosen
2005-09-14 16:47 ` Dmitry A. Kazakov
2005-09-14 17:16 ` Hyman Rosen
2005-09-14 20:20 ` Dmitry A. Kazakov
2005-09-14 20:34 ` Georg Bauhaus
2005-09-14 20:56 ` Hyman Rosen
2005-09-15 7:31 ` Dmitry A. Kazakov
2005-09-15 13:19 ` Hyman Rosen
2005-09-15 13:45 ` Maciej Sobczak
2005-09-15 17:45 ` Dmitry A. Kazakov
2005-09-15 18:54 ` Hyman Rosen
2005-09-16 9:32 ` Dmitry A. Kazakov
2005-09-16 14:52 ` Hyman Rosen
2005-09-16 15:33 ` Jean-Pierre Rosen
2005-09-16 18:37 ` Hyman Rosen
2005-09-16 21:03 ` Dmitry A. Kazakov
2005-09-16 21:33 ` Hyman Rosen
[not found] ` <98ox2x9xvj9z.1uh92dslhvt4g.dlg@40tude.net>
2005-09-17 12:47 ` Georg Bauhaus
2005-09-17 15:56 ` Dmitry A. Kazakov
2005-09-14 16:14 ` Martin Krischik
2005-09-14 16:57 ` Dmitry A. Kazakov
2005-09-14 18:35 ` Martin Krischik
2005-09-14 9:28 ` Alex R. Mosteo
2005-09-14 16:10 ` Martin Krischik
2005-09-13 9:33 ` Georg Bauhaus
2005-09-13 16:37 ` Jeffrey Carter
2005-09-13 18:55 ` Robert A Duff
2005-09-13 22:18 ` Jeffrey Carter
replies disabled
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox