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=-0.9 required=5.0 tests=BAYES_00,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM,WEIRD_PORT autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: a07f3367d7,94d84e4971c0caee,start
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!postnews.google.com!q16g2000yqq.googlegroups.com!not-for-mail
From: Bryan <brobinson.eng@gmail.com>
Newsgroups: comp.lang.ada
Subject: Inheritance with Ada types
Date: Mon, 8 Feb 2010 18:16:14 -0800 (PST)
Organization: http://groups.google.com
Message-ID: 
 <ad9aca45-33dc-4765-a998-44a6b57dbe50@q16g2000yqq.googlegroups.com>
NNTP-Posting-Host: 64.20.18.222
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
X-Trace: posting.google.com 1265681774 22242 127.0.0.1 (9 Feb 2010 02:16:14
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: Tue, 9 Feb 2010 02:16:14 +0000 (UTC)
Complaints-To: groups-abuse@google.com
Injection-Info: q16g2000yqq.googlegroups.com; posting-host=64.20.18.222;
	posting-account=kI3R0woAAAAkETUXcbnWjzzG0TUmJmXv
User-Agent: G2/1.0
X-HTTP-UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US;
	rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7,gzip(gfe),gzip(gfe)
Xref: g2news1.google.com comp.lang.ada:9013
Date: 2010-02-08T18:16:14-08:00
List-Id: <comp.lang.ada>

I'm new to the OOP features of Ada and I'm trying to wrap my head
tagged types.  I've been reading the somewhat abstruse "Ada for
Software Engineers" and while I understand the examples in the text, I
would like to experiment on my own to further my understand.  I'm
trying to figure out how I can correctly--pardon my C++--"subclass" a
base class to create a new derived "class".  I created two simple
packges as follows:

parent.ads:

with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
package Parent is
  type Parent is abstract tagged private;
private
  type Parent is abstract tagged
    record
      Name: Unbounded_String;
    end record;
end Parent;

derived.ads:

with Parent; use Parent;
package Derived is
  type Derived is new Parent with private;
private
  type Derived is new Parent with
    record
      Sub_Name: Unbounded_String;
    end record;
end Derived;

I can compile parent.ads and the object file and ALI file are
produced.  I'm unable to get derived.ads to compile, however.  I get
the following error:

$ gnatmake -c parent derived.ads
gcc -c derived.ads
derived.ads:3:23: subtype mark required in this context
derived.ads:3:23: found "Parent" declared at parent.ads:2
derived.ads:5:23: subtype mark required in this context
derived.ads:5:23: found "Parent" declared at parent.ads:2
gnatmake: "derived.ads" compilation error

If I make the Derived type in a child package of the parent package, I
can get both interfaces to compile.  Perhaps I am misunderstanding
something about Ada OOP, but is it possible to have a derived package
that is not a child package of the base?  Must I use a child package,
or keep the derived type in the same package as the base type?