Re: Private area and child packages

[Stephen Leake <stephen_leake@acm.org>]

danmcleran@hotmail.com writes:

> I don't want any other component to be able to manipulate the
> Secret_Value record component, not even a child package of
> Some_Package.
> 
> Is there any way to do this? In C++, there is something called the
> PIMPL idiom, where you hide implementation detail by holding a pointer
> to an incomplete class, like this:
> 
> //SecretClass.h
> 
> class Implementation;//Class not yet fully defined
> 
> class SecretClass
> {
> public:
> //publicly visible stuff
> private:
> Implementation* pImplementation;
> };

Use the same mechanism in Ada; declare an incomplete type and a
pointer to it:

package Some_Package is
   type Secret_Type is private;
private

   type Really_Secret_Type;
   type Access_Really_Secret_Type is access Really_Secret_Type;

   type Secret_Type is record
      Secret_Value : Access_Really_Secret_Type;
   end record;
end Some_Package;

-- 
-- Stephe