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: 103376,2510538eb4348710
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2001-09-03 02:33:29 PST
Path: 
 archiver1.google.com!newsfeed.google.com!newsfeed.stanford.edu!newsfeeds.belnet.be!news.belnet.be!uni-erlangen.de!news-nue1.dfn.de!news-han1.dfn.de!news.fh-hannover.de!news.cid.net!news.enyo.de!news1.enyo.de!not-for-mail
From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: A generic list package (long)
Date: Mon, 03 Sep 2001 11:53:05 +0200
Organization: Enyo's not your organization
Message-ID: <878zfw8uta.fsf@deneb.enyo.de>
References: <87ae0dp7gn.fsf@deneb.enyo.de> <ubskt2plw.fsf@gsfc.nasa.gov>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Xref: archiver1.google.com comp.lang.ada:12649
Date: 2001-09-03T11:53:05+02:00
List-Id: <comp.lang.ada>

Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov> writes:

>> I'm currently working on a general-purpose low-level list package.
>> The existing approaches were either too heavy-weight, too limited, or
>> covered by an unacceptable license.
>>
>> What do you think about the approach documented below?
>
> I've written a list package with similar goals; see
> http://users.erols.com/leakstan/Stephe/Ada/sal.html.

Thanks.  Your collection looks quite nice.

> I find it curious that you expect the client to provide the "next"
> field/operation, rather than declaring a Node_Type containing the
> user's type and a Next field. Can you elaborate on this?

Using this approach, you can save one indirection in the case of
indefinite types.  (The redirection seems necessary as well if you
need a non-constant view of the actual data.)  In such cases, your
approach seems to result in the following:

                                    +-------------- ...
       +------------------+         |
       |         o========#=======>>| actual data
       |                  |         |
       | fields specific  |         +-------------- ...
       | to the container |
       +------------------+


The getter/setter aproach permits the following:

       +------------------+
       | fields specific  |
       | to the container |
       |                  |
       |    actual data   |
       .                  .
       :                  :


And it is still possible to obtain a non-constant view of the actual
data.

> Your approach leaves everything up to the user; mine ensures that
> garbage is collected appropriately, when necessary; the user only
> needs to provide the appropriate 'free' operation.

I think our approaches are not much different in this regard; if an
element is removed, it is