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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,b0f4738b8e27cca3
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-11-25 08:50:48 PST
Path: 
 archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsgate.cistron.nl!skynet.be!skynet.be!louie!tjb!not-for-mail
Sender: lbrenta@lbrenta
Newsgroups: comp.lang.ada
Subject: Re: Problem with protected type
References: <bpvrlt$6cs$1@online.de> <bpvtb2$a1o$1@online.de>
From: Ludovic Brenta <ludovic.brenta@insalien.org>
User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3
Date: 25 Nov 2003 17:45:17 +0100
Message-ID: <m38ym4xuqq.fsf@insalien.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Organization: -= Belgacom Usenet Service =-
NNTP-Posting-Host: 217.136.19.61
X-Trace: 1069778718 reader3.news.skynet.be 27404 217.136.19.61:38050
X-Complaints-To: usenet-abuse@skynet.be
Xref: archiver1.google.com comp.lang.ada:2927
Date: 2003-11-25T17:45:17+01:00
List-Id: <comp.lang.ada>

"Ekkehard Morgenstern" <ekkehard.morgenstern@onlinehome.de> writes:

> I solved the problem by using a class-wide type access and an init
> procedure:
> 
>  type CoreEvent is tagged private;
>  type CoreEvent_Ptr is access all CoreEvent'Class;
> 
>  function CreateCoreEvent return CoreEvent_Ptr;
> 
>  protected BaseEvent is
>   procedure Init;
>   entry Wait;
>   procedure Signal;
>   procedure ManualMode;
>   procedure AutoMode;
>   procedure Reset;
>   function IsSignaled return Boolean;
>  private
>   EventObject : CoreEvent_Ptr := null;
>   ManualReset : Boolean      := FALSE;
>  end BaseEvent;
> 
> But why is this necessary?

Because, I think, CoreEvent is not completely defined at the point
where you use it inside BaseEvent.  Therefore the compiler does not
know how much memory to allocate for a BaseEvent.

By contrast, the access type is completely defined, so you can use it
in the BaseEvent.

> And can I create inheritable protected classes?

No.  This has been proposed as an extension to the language [1] back
in 2000, but the discussions concluded that there was no demand for
this feature from paying customers, so therefore no compiler vendors
were going to implement it.

[1] http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00250.TXT?rev=HEAD

-- 
Ludovic Brenta.