Re: Type vs subtype about visibility of parent's private full definition

[Adam Beneschan <adam@irvine.com>]

On Wednesday, May 15, 2013 1:13:00 AM UTC-7, Hibou57 (Yannick Duchêne) wrote:
> Hi all,
> 
> I already encountered something similar in the past, and it's back again.  
> I can only solve it using a subtype instead of a type-new where I  
> initially want a type-new, so I'm not happy with using subtype.
> 
> The case: a child package don't see the full definition of a type from the  
> private part of its parent package when it derives from that type as a  
> type-new.
> 
> Below is an example, using a discriminant, which is not required to expose  
> the visibility issue, but which is the reason why I'm not happy to not be  
> able to derive a type-new instead of a subtype: I can't force static-check  
> as I expected. If the discriminant was not part of the party, I won't  
> bother. That's the reason why the example makes use of a discriminant and  
> I see the case as an issue.

> Example:

>      package Parents is
>         pragma Pure; 
>         type Discriminant_Type is
>            range 1 .. 5;
> 
>         type Instance_Type
>           (Discriminant : Discriminant_Type) is
>            private;
> 
>      private
>         type Instance_Type
>           (Discriminant : Discriminant_Type) is
>            record
>               Value : Integer;
>            end record;
>      end Parents;
> 
>      package Parents.Childs is
>         pragma Pure;
>         subtype Parent_Type is
>            Parents.Instance_Type;
>         type Instance_Type is
>            new Parent_Type
>              (Discriminant => 2);
>         function Value
>           (Object : Instance_Type)
>            return Integer;
>      private
>         function Value
>           (Object : Instance_Type)
>            return Integer
>            is (Object.Value); -- << Error here
>      end Parents.Childs;
> 
> 
> I did not check the RM, however I'm blocked if I do this, as GNAT has  
> complaints with `is (Object.Value)`, and grumbles:
> 
>      no selector "Value" for private type derived from "Instance_Type"

> What are your opinions about this issue?

7.3.1(4) says that the Value component should be visible at that point.  This is a compiler bug.

                             -- Adam