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-Thread: 103376,672558c47d86bb1d
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news1.google.com!proxad.net!news.cs.univ-paris8.fr!newsfeed.vmunix.org!newsfeed01.sul.t-online.de!newsmm00.sul.t-online.de!t-online.de!news.t-online.com!not-for-mail
From: Martin Krischik <martin@krischik.com>
Newsgroups: comp.lang.ada
Subject: Re: Hierarchy destruction in Ada
Date: Sun, 12 Dec 2004 17:52:10 +0100
Organization: None
Message-ID: <1764085.COooLuJmQE@linux1.krischik.com>
References: <fa59671.0412120718.61093406@posting.google.com>
Reply-To: martin@krischik.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7Bit
X-Trace: news.t-online.com 1102870427 00 21446 Lxy4X6yLbPT0IbM 041212 16:53:47
X-Complaints-To: usenet-abuse@t-online.de
X-ID: ZYOIC8ZHwec6rnGfhMLn3Mor-T9YslwyDTvdjl4QyyYLCskdf52-EE
User-Agent: KNode/0.8.0
Xref: g2news1.google.com comp.lang.ada:6902
Date: 2004-12-12T17:52:10+01:00
List-Id: <comp.lang.ada>

Michael Mounteney wrote:

> Ada 95 provides a mechanism with tagged and type'class to allow
> dynamic dispatch. So if one has:
> 
> procedure something (O : basetype'class) is
> begin
>      enact (O);
> end something;
> 
> then as we all know, with the appropriate redefinitions of enact ()
> for the subtypes of basetype, we have dynamic dispatch.  But what
> about deallocation ? I want to declare:
> 
> type handle is access all basetype;

The trick is:

type handle is access basetype'Class;

> procedure dispose (ptr : in out handle);

If you want to write a "dispose" function you should not use "access all".
Reason: access all allows any kind of access but the "dispose" needs the
right type of access to work properly. i.E:

declare
   X : aliased basetype;
begin
   dispose (X'Access);
end;

You don't want that, don't you? If you need the "all" features for other
reasons then consider:

type pool_handle is access basetype'Class;
type any_handle is access all basetype'Class;

> and can't see how to make this deallocate the correct object.
> Obviously, one can dynamically dispatch on ptr.all but it seems
> impossible to solve the complete problem without an unchecked
> conversion. Anyone ?

When you deallocate an "access basetype'Class" then the propper finalisation
is done. 

With Regards

Martin

-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com