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-Thread: 103376,5e53057e86953953
X-Google-Attributes: gid103376,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news1.google.com!news2.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local02.nntp.dca.giganews.com!nntp.telenor.com!news.telenor.com.POSTED!not-for-mail
NNTP-Posting-Date: Tue, 17 Jun 2008 04:14:59 -0500
From: Reinert Korsnes <a@b.no>
Subject: Re: Question on initialization of packages
Newsgroups: comp.lang.ada
Date: Tue, 17 Jun 2008 11:14:59 +0200
References: <y4adnXtddsFN7crV4p2dnAA@telenor.com>
 <1pok6brk3yyxf$.ct5gwnf4g97p$.dlg@40tude.net>
User-Agent: KNode/0.10.4
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7Bit
Message-ID: <KredncLZKqYOHcrVRVnzvQA@telenor.com>
X-Usenet-Provider: http://www.giganews.com
X-Trace: 
 sv3-lPlzlbHXIbWchBDti5rdrhpGTQlJEwCaYs0matoXt7b0rjogz8xDUi5yd78TBo0KkjzWhq0DMqGmoBT!BfMU9sLqOLyiJzI6Cz02F1fSL/1Mbn96YhBWvPOJSOQaGrM7D6ki63CrzZ80F4oRN5r+q46vtWE=
X-Complaints-To: news-abuse@telenor.net
X-DMCA-Complaints-To: news-abuse@telenor.net
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint
 properly
X-Postfilter: 1.3.39
Xref: g2news1.google.com comp.lang.ada:735
Date: 2008-06-17T11:14:59+02:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov wrote:

> On Tue, 17 Jun 2008 10:07:43 +0200, Reinert Korsnes wrote:
> 
>> Assume the package definition given below,
>> and the follow code in my program:
>> 
>>    type Message_t;
>>    type Message_ta is access Message_t;
>>    package Message_Stack_p is new Stacks(Message_ta);
>>    Send_Stack    : Message_Stack_p.Stack;
>> 
>> Question: How can I be sure that "Send_Stack" is empty
>> at the start of the program execution ?
> 
> Hmm, "sure" in which sense? To make it visible for the reader? To specify
> in the contract of Stack that it is initially empty?

Yes, yes, to make it visible for the reader.

> 
> As for implementation you posted, the stack is empty, because instances of
> access types are initialized with null (when not explicitly initialized

Yes, but I do not like things depend on the particular implementation :-)


> otherwise). Below you declare:
> 
>>   type Stack is access Cell;
> 
> And
> 
>    Send_Stack : Message_Stack_p.Stack; -- This will be null = empty
> 
> 
> Now side comments:
> 
> 1.
> 
>>   procedure Pop(S: in out Stack; X: out Item) is
>>   begin
>>     X := S.Value;
>>     S := S.Next;
>>   end;
> 
> This is a memory leak. If you allocated a stack element on push, you
> should free it on pop.

How I free it?  I may not have a deep enough understanding here :-)

>  
> 2. Package initialization is achieved as follows:
> 
> package body P is
>    ...
> begin
>    ... -- Initialize package stuff
> end P;
> 
> 3. Package initialization cannot help you here, because the package
> declares an abstract data type of which objects can be created long after
> the package itself was elaborated (initialized).

But I would like to make it clear for all that the stack is
empty at the start of my program !  (also after that I may
change the implementation).

> 
> 4. You have messages. Pointers to messages. These pointers are copied into
> dynamically allocated linked list called stack.
> 
> How are you going to maintain this? Do you want to prevent messages from
> being copied? Then you should reconsider the design of messages allowing
> their queuing without stacks. Alternatively, do you want to copy messages
> upon queueing (to marshal them)? Then the queue should deal with
> unconstrained objects:
> 
>    generic
>       type Message (<>) is private;
>    package Queue is
>       ...
> 

I want to "stack away" messages to be processed later.
Copied, deleted etc.

reinert