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
Path: 
 g2news2.google.com!news1.google.com!goblin2!goblin.stu.neva.ru!fi.sn.net!newsfeed1.tdcnet.fi!news.song.fi!not-for-mail
Date: Sun, 11 Oct 2009 22:54:34 +0300
From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Organization: Tidorum Ltd
User-Agent: Mozilla-Thunderbird 2.0.0.22 (X11/20090706)
MIME-Version: 1.0
Newsgroups: comp.lang.ada
Subject: Re: Runtime type selection
References: 
 <2c15c8a6-b555-4d08-8fe6-f77cb207e7a6@k33g2000yqa.googlegroups.com>
 	<4ad20fd5$0$26308$4f793bc4@news.tdc.fi>
 <61d081f4-cccc-4575-927f-5c400b73ff90@k19g2000yqc.googlegroups.com>
In-Reply-To: 
 <61d081f4-cccc-4575-927f-5c400b73ff90@k19g2000yqc.googlegroups.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Message-ID: <4ad23819$0$6256$4f793bc4@news.tdc.fi>
NNTP-Posting-Host: 81.17.205.61
X-Trace: 1255290905 news.tdc.fi 6256 81.17.205.61:49112
X-Complaints-To: abuse@tdcnet.fi
Xref: g2news2.google.com comp.lang.ada:8674
Date: 2009-10-11T22:54:34+03:00
List-Id: <comp.lang.ada>

xorque wrote:
> On Oct 11, 5:02 pm, Niklas Holsti <niklas.hol...@tidorum.invalid>
> wrote:
>> Keep a list or array of (accesses to) a factory function for each
>> possible (derived) type.
> 
> 'Lo,
> 
> That does sound like the sort of thing I'd have done in C.

Yes. Ada makes it easier since you can use elaboration-time statement 
blocks in package bodies to register stuff.

> I still
> have a nagging sensation that Ada actually provides other means to
> do this based on such things as the 'Tag attribute.

Did you read about the package Ada.Tags (RM 3.9)? There is a generic 
function Ada.Tags.Generic_Dispatching_Constructor that takes a tag as 
parameter and creates an object with that tag, but I don't hink there is 
any way to find the tags for all types in a given derivation class. So 
even with  Ada.Tags.Generic_Dispatching_Constructor your program still 
has to register the types, or their tags, or a prototype object of each 
type, to create the program-accessible set of types/tags that can be in 
the graph.

Perhaps some expert can explain why this reflection capability (find 
tags for all derived types in a class) was not included in Ada.Tags? 
Perhaps because Ada run-time systems do not need such a function for 
their own purposes?

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .