From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Instantiating private types with discriminants?
Date: Thu, 11 May 2006 09:44:20 +0200
Date: 2006-05-11T09:44:18+02:00 [thread overview]
Message-ID: <i4rqev137oq1.161jykmec6dts.dlg@40tude.net> (raw)
In-Reply-To: HeidnX-p77c9_f_ZRVny1Q@pipex.net
On Wed, 10 May 2006 16:52:32 -0500, Rick H wrote:
> But all this has a side-effect that I haven't considered: the fact
> that a variable declared as a class-wide type *requires* initialization
> means that the compiler can determine the variable's type statically.
No. It only means that the type should be determinable at run-time. There
are may ways to do it. You can call a function with a class-wide result.
It might be especially interesting to take a look at S'Class'Input
attribute. It "dispatches" on a "bare" tag. [ Ada 2005 will offer a
mechanism for fully user-defined things like this. See
Generic_Dispatching_Constructor. ]
> This means that the following will raise a constraint error:
> declare
> Var_A : General_T'Class := Get (10); -- Type_A
> begin
> Put (Var_A);
> Ada.Text_IO.New_Line;
> Var_A := Get (100.0); -- Type_B - constraint error!
> Put (Var_A);
> end;
Yes, but this is a different thing. You cannot change tag, either
dynamically or statically determined. Type mutators are no-no in Ada's type
system.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2006-05-11 7:44 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-09 13:17 Instantiating private types with discriminants? rick H
2006-05-09 13:45 ` Georg Bauhaus
2006-05-09 14:06 ` rick H
2006-05-09 13:56 ` Ludovic Brenta
2006-05-09 14:24 ` rick H
2006-05-09 19:48 ` Ludovic Brenta
2006-05-09 14:05 ` Dmitry A. Kazakov
2006-05-09 14:48 ` rick H
2006-05-09 15:20 ` Jerry Petrey
2006-05-09 15:42 ` rick H
2006-05-09 15:53 ` Avoiding use Ada.Tags (was Re: Instantiating private types with discriminants?) Alex R. Mosteo
2006-05-09 16:01 ` Instantiating private types with discriminants? Dmitry A. Kazakov
2006-05-10 7:42 ` rick H
2006-05-10 9:09 ` Ludovic Brenta
2006-05-10 11:49 ` Georg Bauhaus
2006-05-10 13:44 ` rick H
2006-05-10 14:21 ` Ludovic Brenta
2006-05-10 15:10 ` rick H
2006-05-10 15:45 ` Ludovic Brenta
2006-05-10 14:41 ` Dmitry A. Kazakov
2006-05-10 15:34 ` rick H
2006-05-10 19:01 ` Georg Bauhaus
2006-05-10 19:05 ` Ludovic Brenta
2006-05-10 21:52 ` Rick H
2006-05-11 1:17 ` Jeffrey R. Carter
2006-05-11 7:44 ` Dmitry A. Kazakov [this message]
2006-05-11 8:27 ` rick H
2006-05-11 10:28 ` Dmitry A. Kazakov
2006-05-11 15:59 ` Robert A Duff
2006-05-12 7:37 ` Dmitry A. Kazakov
2006-05-12 9:24 ` Georg Bauhaus
2006-05-12 12:40 ` Dmitry A. Kazakov
2006-05-12 18:25 ` Randy Brukardt
2006-05-09 19:57 ` "Use" and "=" for Tags (was: Re: Instantiating private types with discriminants?) Jeffrey R. Carter
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