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From: danmcleran@hotmail.com
Newsgroups: comp.lang.ada
Subject: Re: Possible Ada deficiency?
Date: 1 Jan 2005 11:43:15 -0800
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Date: 2005-01-01T11:43:15-08:00
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The point I'm trying to make is that if I want to write a package and
hide certain information from all future child packages, a new
construct is needed. One might want to share certain information with
child packages, but force child packages to use a public or private
interface for other information. For the sake of discussion, let's say
that a new keyword, 'concealed', meant that this section could not be
seen by the outside world, including child packages. One could then
write a package with a public area, a private area (child packages
could see this area), and a concealed area that no one, including child
packages, could see. In this example, Secret_Type is a type that I want
completely hidden from the outside world. There is a public interface,
Print_Secret_Value, that anyone can call, and a private interface,
Change_Concealed_Value, that is only callable from with the package
body and all child packages. Simple example:

-- This is not Ada!

package Some_Package is
--public area
type Secret_Type is concealed;

procedure Print_Secret_Value (Value : in Secret_Type);

private
--Child packages can see here
procedure Change_Concealed_Value (New_Value : in Secret_Type);
concealed
--Child packages cannot see here, they must use the public and/or
private interface
type Secret_Type is record
Secret_Value : Integer;
end record
end Some_Package;