From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,e044473b43baaf18
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-05-26 01:27:40 PST
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!headwall.stanford.edu!fu-berlin.de!uni-berlin.de!dialin-145-254-037-224.arcor-ip.NET!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: automatic tag conversion?
Date: Mon, 26 May 2003 10:29:59 +0200
Organization: At home
Message-ID: <basj5q$32qm4$1@ID-77047.news.dfncis.de>
References: <bam9ec$asg$1@news.cs.tu-berlin.de>
 <bamcht$fs8$1@news.cs.tu-berlin.de> <baoapa$pm7$1@a1-hrz.uni-duisburg.de>
 <bararj$hk4$1@news.cs.tu-berlin.de>
Reply-To: mailbox@dmitry-kazakov.de
NNTP-Posting-Host: dialin-145-254-037-224.arcor-ip.net (145.254.37.224)
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7Bit
X-Trace: fu-berlin.de 1053937659 3238596 145.254.37.224 (16 [77047])
User-Agent: KNode/0.7.1
Xref: archiver1.google.com comp.lang.ada:37776
Date: 2003-05-26T10:29:59+02:00
List-Id: <comp.lang.ada>

Stephan Heinemann wrote:

> I am using generic sets like this one:
> 
> generic
>     type Element is private;
> package CNAda.Utils.Sets is
> 
>     type Set is private;
>     type LookProcedure is access procedure (e: in Element);
>     type MapProcedure is access procedure (e: in out Element);
> 
>     procedure empty(s: in out Set);
>     procedure insert(e: in Element; s: in out Set);
>     procedure remove(e: in Element; s: in out Set);
> 
>     procedure look(lookp: in LookProcedure; s: in Set);
>     procedure map(mapp: in MapProcedure; s: in Set);
[...]
> I use the following for instantiation of this package.
> 
>     type Node is abstract new Component with private;
>     type NodeClassAccess is access all Node'Class;
> 
> package NodeClassAccessSets is new CNAda.Utils.Sets(NodeClassAccess);
> 
> NodeClassAccessSets.Set is a component within another tagged (record)
> type - a Net.
> There are various derived types of Node like Transition, Place and
> further Operation, Socket, Port and so on....
> 
> I want to apply a LookProcedure on the set for example to
> print all elements of this set. There is a primitive operation print
> defined on the types within the hierarchy:
> 
> procedure print(n: access Node) is abstract;
> procedure print(t: access Transition);
> procedure print(p: access Place);
> 
> ...and so on. I want the system to dispatch to the most special variant
> of the procedure for the apropriate derived type like:
> 
> NodeClassAccessSets.look(print'Access, s);
> 
> It is clearly possible to pass in a NodeClassAccess variable with any
> derived *ClassAccess value into a print procedure defined as above even if
> the print procedure was not overridden by the new derived type.
> The system would always dispatch the most special case, am I right?

No, Element is of NodeClassAccess which is different from anonymous "access 
Node" (that will dispatch). Thus LookProcedure.all is not dispatching at 
all. However it will be sort of "class-wide" when NodeClassAccess is 
class-wide, as it is. So you practically have everything to make it 
working. Just define a wrapper in the same package, where Node is defined:

procedure Print_Any (Ptr : NodeClassAccess) is
begin
   Print (Ptr); -- Dispatches
end Print_Any;

Then

NodeClassAccessSets.look (Print_Any'Access, s);

should work as expected.

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de