Re: tagged primitive operation and freezing

[troll <wisniewski.ru@gmail.com>]

But only if it is tagged. untagged type, even though frozen, DOES
compile.

On Nov 13, 5:24 am, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
> troll writes on comp.lang.ada:
>
>
>
>
>
> > generic
> >   type Object_T is private;
> > procedure blah ( Param : Object_T );
>
> > -------
>
> > with blah;
> > package oops is
> >   type a is tagged null record;  -- any tagged type
>
> >  -- must be a type extension to induce failure:
> >   type Flight_T is new a with null record;  -- fail
>
> >   function b (Flight : in Flight_T) return String;
>
> >   procedure c is new blah (Object_T => Flight_T);
>
> > end;
>
> I think the reason why this is illegal is because c is a primitive
> operation of Flight_T; at the same time, using Flight_T as an actual
> generic parameter freezes Flight_T just before the declaration of this
> new primitive operation.  Therefore the declaration of c is illegal.
>
> You can work around this by wrapping Flight_T in a package:
>
> generic
>   type Object_T is private;
> procedure blah ( Param : Object_T );
>
> with blah;
> package oops is
>   type a is tagged null record;  -- any tagged type
>
>   package Flight is
>   -- must be a type extension to induce failure:
>      type T is new a with null record;
>      function b (Flight : in T) return String;
>   end Flight; -- this freezes Flight_T
>
>   procedure c is new blah (Object_T => Flight.T); -- non-primitive
>
> end oops;
>
> --
> Ludovic Brenta.- Hide quoted text -
>
> - Show quoted text -