Re: ada and final/sealed classes

[Matthew Heaney <matthewjheaney@earthlink.net>]

onsbomma@hotmail.com (Hans Van den Eynden) writes:

> I want to prevent someone from inheriting from a type I made (for
> security purposes). I am a junior Ada programmer and I know this
> possible in Java (final class) and C# (sealed class). Is this also
> possible in Ada???

Not really, no.

Ada is designed such that there is a lexical distinction for a type that
has visibility to the representation of another type.  

The way this works is that derived types in a class that have access to
the representation of the parent type must be declared in child
packages:

package P is
   type T is tagged limited private;
   ...
private
   type T is tagged limited record
     ... -- lots of secret stuff here
   end record;
end P;

package P.C is
   type NT is new T with private;
   ...
private
   type NT is new T with record
      ... -- more secret stuff here
   end record;
end P.C;

Here, type P.C.NT has visibility to the private presentation of type
P.T.  That fact is ennunciated since NT is declared in the same
subsystem (rooted at package P) as type T.