Re: Preventing private procedure visibility being made public through extension

[Jere <jhb.chat@gmail.com>]

On Sunday, May 21, 2017 at 5:20:36 PM UTC-4, Dmitry A. Kazakov wrote:
> On 2017-05-21 22:21, Jere wrote:
> 
> > The actual use case has
> > them in separate packages, but the problem is the same:
> 
> No. Robert meant that when you declare a subprogram in a separate 
> package [more precisely after the type's freezing point] it will not 
> become a primitive operation. A non-primitive operation is simply not 
> inherited and if not visible, is gone. Being not inherited is a very 
> important point, it will be rejected for derived types even if visible. 
> Consider this:
> 
>     package Base is
>        type Base_Type is tagged null record;
>     end Base;
> 
>     package Base_Something is
>        procedure Something (X : in out Base_Type; Y : Integer) is null;
>     end Base_Something;
> 
>     package Derived is
>        type Derived_Type is new Base_Type with null record;
>     end Derived;
> 
>     package Derived_Something is
>        procedure Something (X : in out Derived_Type; Y : String) is null;
>     end Derived_Something;
> 
>     use Base, Derived, Base_Something, Derived_Something;
>     X : Base_Type;
>     Y : Derived_Type;
> begin
>     Something (X, 1);   -- OK
>     Something (Y, 2);   -- Type error!
>     Something (Y, "2"); -- OK
> 
> -- 
> Regards,
> Dmitry A. Kazakov
> http://www.dmitry-kazakov.de

Yes, but in the current case, Base_Type is already 
defined in a library with the procedures in 
the same package as the type.  However, this is a good 
point for when I make my own types.