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=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Parent/child dependencies and internal library units
Date: Wed, 23 Jul 2014 17:47:55 +0100
Organization: A noiseless patient Spider
Message-ID: <ly38dsrphg.fsf@pushface.org>
References: <lqoncd$ue7$1@speranza.aioe.org>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: mx05.eternal-september.org;
 posting-host="f008dfb2a20cab2735f9b6a28e892fd7";
	logging-data="28714"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX1+WbOLbhyn/N4OC0/G5jCoLV/qFwGWErp0="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (darwin)
Cancel-Lock: sha1:94pgsNd9Q51t5QJIOsn2nqChpTo=
	sha1:4H8I2NQ56CiDkKvA8t+v2mMXZPI=
Xref: news.eternal-september.org comp.lang.ada:21159
Date: 2014-07-23T17:47:55+01:00
List-Id: <comp.lang.ada>

Victor Porton <porton@narod.ru> writes:

> I noticed that child units depend on their parents.
>
> As such making parent dependent on a child makes a dependency loop.
>
> Before noting this feature of Ada language, I thought parent units could be 
> implemented based on their child units, but that does not work, because 
> making parents dependent on children is a circular dependency.
>
> So, my question:
>
> What is a good way to create "internal" or "implementation" units for a 
> unit? Should I create a *.Internal.* hierarchy of packages?

I dare say there are uses which could make this not work (possibly
involving initialisation of objects in specs via function calls, leading
to access-before-elaboration) but you can make a parent body depend on a
child spec.

If the implementation is meant to be hidden from users outside the
parent, consider using private child packages.

   package Hierarchy is
      procedure Tell;
   end Hierarchy;

   private package Hierarchy.Internal is
      procedure Tell;
   end Hierarchy.Internal;

   with Ada.Text_IO;
   package body Hierarchy.Internal is
      procedure Tell is
      begin
         Ada.Text_IO.Put_Line ("Hierarchy.Internal");
      end Tell;
   end Hierarchy.Internal;

   with Ada.Text_IO;
   with Hierarchy.Internal;
   package body Hierarchy is
      procedure Tell is
      begin
         Ada.Text_IO.Put_Line ("Hierarchy");
         Internal.Tell;
      end Tell;
   end Hierarchy;

   procedure Hierarchy.Main is
   begin
      Tell;  -- this is Hierarchy.Tell
   end Hierarchy.Main;