From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Equivalent of dynamic_cast (downcast) for tagged types
Date: Thu, 27 Jan 2011 17:18:03 +0100
Date: 2011-01-27T17:18:04+01:00 [thread overview]
Message-ID: <evoxe8yl0jfw.guw86vvdhuzb.dlg@40tude.net> (raw)
In-Reply-To: 375fb596-ab12-4cb0-a190-53d62b94b2e4@e9g2000vbi.googlegroups.com
On Thu, 27 Jan 2011 07:46:33 -0800 (PST), Maciej Sobczak wrote:
> Unfortunately I need to HACK some equivalent of dynamic_cast in Ada.
>
> There is a limited tagged type T deriving from Limited_Controlled and
> Some_Interface as well.
> There is also a procedure like this:
>
> procedure Foo (X : in Some_Interface'Class);
>
> Inside Foo I would like to check if X is indeed T and if so, I would
> like to dynamic_cast to it and execute some operation on T. That
> operation is in fact declared in Some_Interface anyway, but I would
> like to avoid the dispatching call. I would also like to avoid any
> potential data copying, so access types are welcome.
You don't need access type, tagged types are by-reference anyway.
> In C++ it would look like this:
>
> void foo(some_interface & x)
> {
> T * p = dynamic_cast<T*>(&x);
> if (p != NULL)
> {
> // indeed x is of type T
> p->do_something_for_me();
> }
> }
if X in T'Class then
Do_Something (T (X)); -- No dispatch
end if;
The above is a bad idea, because X might be a descendant of T which has
overridden Do_Something. So you might be looking for this
if X'Tag = T'Tag then -- X is of T
Do_Something (T (X)); -- No dispatch
end if;
> If you say that I should not do this because it is not good practice,
> then I will quickly answer that GNAT should not randomly call Adjust
> on my limited (!) objects.
Adjust is not called on limited objects.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2011-01-27 16:18 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-27 15:46 Equivalent of dynamic_cast (downcast) for tagged types Maciej Sobczak
2011-01-27 16:18 ` Dmitry A. Kazakov [this message]
2011-01-27 17:10 ` J-P. Rosen
2011-01-27 17:35 ` Dmitry A. Kazakov
2011-01-27 22:49 ` Maciej Sobczak
2011-01-27 17:50 ` Georg Bauhaus
2011-01-27 22:35 ` Maciej Sobczak
2011-01-28 5:07 ` Yannick Duchêne (Hibou57)
2011-01-28 9:16 ` Dmitry A. Kazakov
2011-01-28 13:11 ` AdaMagica
2011-01-28 14:13 ` Dmitry A. Kazakov
2011-01-28 23:51 ` Randy Brukardt
2011-01-29 0:55 ` Adam Beneschan
2011-01-28 16:44 ` Adam Beneschan
2011-01-28 17:21 ` Dmitry A. Kazakov
2011-01-29 0:12 ` Randy Brukardt
2011-01-29 8:47 ` Dmitry A. Kazakov
2011-01-28 17:33 ` Adam Beneschan
2011-01-28 15:13 ` Maciej Sobczak
2011-01-28 17:47 ` Robert A Duff
2011-01-28 22:04 ` Maciej Sobczak
2011-01-30 20:22 ` Stephen Leake
2011-01-31 9:04 ` AdaCore, user community and communication channels Maciej Sobczak
2011-01-31 10:42 ` Georg Bauhaus
2011-01-27 19:33 ` Equivalent of dynamic_cast (downcast) for tagged types Adam Beneschan
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