Re: Preventing private procedure visibility being made public through extension

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

On Thursday, May 25, 2017 at 3:40:01 PM UTC-4, Randy Brukardt wrote:
> Your probably having trouble with the appropriaate view of My_Type. The full 
> type of My_Type has both versions of Create (of course), as it inherits from 
> View_Type. If you try to extend somewhere where that full view is visible, 
> then that extension too will get both Creates. (That includes in the body 
> and in any child packages.)
> 
> OTOH, an extension somewhere that only has visibility on the private type, 
> you should only get one (visible) Create. (But the other one is still 
> inherited, it just can't be called directly.)
> 
> I could go into more detail if you need that; it would help to have a full 
> compilable example in that case so I can see where everything is declared.
> 
>                            Randy.
> 
> 

This might be a better example.  I have 3 tiers:  Base/Derived/More_Derived

More_Derived publicly inherits off of Base but privately inherits off of
Derived. 

Derived provides a Something procedure and More_Derived provides a Something
procedure but uses a different signature and is not overriding (I double
checked by putting "overriding" with it and noted the compiler error).

More_Derived does not have private view of Derived, but GNAT still says
there is a ambiguity.  I don't see how More_Derived has a private
view of Derived, so I think this is a bug, but I might be missing
something.

main.adb
*******************************************
with Base;
with Derived;
with More_Derived;

procedure Main is
   p : Base.Derived_Param;
   
   subtype My_Type is More_Derived.More_Derived_Type;
   
   m : My_Type;
begin
   m.Something(p);  -- ERROR:  ambiguous call to Something
end Main;
*******************************************


base.ads
*************************************************
package Base is

   type Base_Param is tagged null record;
   type Derived_Param is new Base.Base_Param with null record;

   type Base_Type is tagged null record;

end Base;
*************************************************


derived.ads
*************************************************
with Base;

package Derived is

   type Derived_Type is new Base.Base_Type with null record;

   procedure Something
      (Obj   : in out Derived_Type;
       Value :        Base.Base_Param'Class)
   is null;

end Derived;
*************************************************


more_derived.ads
*************************************************
with Base;
with Derived;

package More_Derived is 
   
   type More_Derived_Type is new Base.Base_Type with private;
   
   procedure Something
      (Obj   : in out More_Derived_Type;
       Value :        Base.Derived_Param'Class)
   is null;
   
private
   
   type More_Derived_Type is new Derived.Derived_Type with null record;
   
end More_Derived;
*************************************************

If I don't use the subtype in main.adb, it compiles fine.