Re: Private area and child packages

[Jeffrey Carter <spam@spam.com>]

danmcleran@hotmail.com wrote:

> What about using Ada's Limited_Controlled type? Then, since no copies
> could be made, I could do something like this:
> 
> with Ada.Finalization;
> 
> package Some_Package is
> type Secret_Type is tagged limited private;
> private
> type Implementation_Type;
> type Implementation_Access_Type is access Implementation_Type;
> type Secret_Type is new Ada.Finalization.Limited_Controlled with
> record
> Implementation_Access : Implementation_Access_Type := null;
> end record;   
> end Some_Package;

Don't forget to override Finalize.

This doesn't really do what you want, since a child can see and copy the 
access component:

package body Some_Package.Child is
    A : Implementation_Access_Type

    procedure Op (L : Secret_Type) is
       -- null;
    begin -- Op
       A := L.Implementation_Access;
    end Op;

    ...
end Some_Package.Child;

It's possible for the actual of L to go out of scope and be finalized, 
deallocating L.Implementation_Access, while A is still around, a 
dangling reference.

-- 
Jeff Carter
"Now look, Col. Batguano, if that really is your name."
Dr. Strangelove
31