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From: danmcleran@hotmail.com
Newsgroups: comp.lang.ada
Subject: Re: Possible Ada deficiency?
Date: 9 Jan 2005 09:23:25 -0800
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Date: 2005-01-09T09:23:25-08:00
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>By the way, is the original poster worried that subunits can see all
>kinds of hidden stuff in the parent body? That case seems less
>worrisome, because the parent mentions the names of all subunits.
>The language could allow the same thing for children (but it shouldn't
>*require* it).

I'm not sure what you mean by this. My only point is that there is no
way to hide internal representation details from child packages. I have
read the Ada95 rationale and I understand why child packages are
allowed and why they have the visibility they have. What I would like
in Ada is the power to hide implementation detail from child packages,
if I choose to do so.

I would propose adding a new keyword, 'concealed', to allow a package
writer to hide certain areas from all child packages.

package Some_Package is
type Not_So_Secret_Type is private; --Child packages can see here
type Some_Type is concealed; --Child package cannot see here
private
--Child package can change Not_So_Secret_Value
type Not_So_Secret_Type is record
Not_So_Secret_Value : Integer := 0;
end record
concealed
--Child packages cannot change Secret_Value directly
type Some_Type is record
Secret_Value : Integer := 1;
end record
end Some_Package

With the addition of this construct, a package writer can choose what
areas should be directly visible to child packages, and what areas
should not. This would force a child package to use the parent
package's public interface when dealing with objects of type Some_Type,
rather than having full visibility into Some_Type's internal
representation.