From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: What makes a procedure call 'dispatching' in Ada?
Date: Fri, 20 Nov 2009 14:27:14 +0100
Date: 2009-11-20T14:27:14+01:00 [thread overview]
Message-ID: <hnu4yrsf2d2d.1v1o4ujm3sccp$.dlg@40tude.net> (raw)
In-Reply-To: he64pl$d8i$1@nntp.ilk.net
On Fri, 20 Nov 2009 14:15:33 +0100, Markus Schoepflin wrote:
> I'm trying to fell may way around object oriented Ada programming, and I
> think I must be missing something absolutely basic.
> Please consider the following package:
>
> ---%<---
> package FOOS is
>
> type FOO is abstract tagged null record;
>
> procedure P (THIS : in FOO);
> procedure A (THIS : in FOO) is abstract;
>
> end FOOS;
>
> package body FOOS is
>
> procedure P (THIS : in FOO)
> is
> begin
> A (THIS);
> end;
>
> end FOOS;
> --->%---
>
> When trying to compile this, I get:
>
> foos.adb:6:07: call to abstract function must be dispatching
> gnatmake: "foos.adb" compilation error
>
> What is the compiler trying to tell me here? And how do I go about calling
> abstract procedures?
It tells you that the type of THIS is FOO, so you cannot call to A, because
A is not defined on FOO.
If P is to be defined in terms of any type from the class FOO, then P has
to be declared differently (class-wide):
package FOOS is
type FOO is abstract tagged null record;
procedure P (THIS : in FOO'Class);
-- I am SAME for the whole class rooted in FOO
procedure A (THIS : in FOO) is abstract;
-- I have an implementation in each instance of the class except
-- for the abstract ones like FOO.
end FOOS;
package body FOOS is
procedure P (THIS : in FOO'Class) is
begin
A (THIS);
-- I do not know what kind of FOO is THIS. So I
-- dispatch to A according to the tag of THIS.
end P;
end FOOS;
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2009-11-20 13:27 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-20 13:15 What makes a procedure call 'dispatching' in Ada? Markus Schoepflin
2009-11-20 9:31 ` stefan-lucks
2009-11-20 14:10 ` Niklas Holsti
2009-11-20 13:27 ` Dmitry A. Kazakov [this message]
2009-11-20 13:43 ` Markus Schoepflin
2009-11-20 13:54 ` RasikaSrinivasan@gmail.com
2009-11-20 13:58 ` Markus Schoepflin
2009-11-20 14:19 ` Niklas Holsti
2009-11-21 14:07 ` Peter C. Chapin
2009-11-20 14:00 ` Niklas Holsti
2009-11-20 14:10 ` Dmitry A. Kazakov
2009-11-20 13:56 ` Niklas Holsti
2009-11-20 14:31 ` Dmitry A. Kazakov
2009-11-20 15:00 ` Niklas Holsti
2009-11-20 18:44 ` Dmitry A. Kazakov
2009-11-20 20:09 ` Niklas Holsti
2009-11-20 20:59 ` Dmitry A. Kazakov
2009-11-20 14:54 ` Ludovic Brenta
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