Re: Which compiler is correct?

[jsa@alexandria.organon.com (Jon S Anthony)]

In article <867075736.16958@dejanews.com> Mats.Weber@elca-matrix.ch writes:

<<emailed as well...>>


> Sorry, but I still don't get it. What is wrong with the following
> interpretation of the rules ?
> 
> package a is
>     type x is tagged private;
> private
>     type x is tagged record
>         i:integer;
>     end record;
> end a;
> package a.b is
>     type y is new x with private;
> 
> This establishes, among other things, that y inherits x's components.

Aha!  This is where you are confused.  This does _not_ establish that
y inherits x's components because they are not yet visible.  See 7.3.1
and pay particular attention to (3).


> private
>     type y is new x with record
>         j:integer;
>     end record;

It is at this point that x's components are visible and it is only at
that point (when they become visible) that they are implicitly
declared.

> end a.b;
> with a.b;
> package a.c is
>     type z is new a.b.y with private;
> 
> As y is visibly derived from x, we know that z is an ancestor of x.

True, but since a.c does not see the private portion of a.b it does
not see the implicitly declared components of y inherited from x,
because the declaration that it does see does not have them.

> full declaration of x. The "additional characteristic" that y has an i
> component becomes visible

No, since a.c does not have visibility to a.b's private portion, these
components are not directly visible (they are there, you just can't
see them unless you convert).

> (because y inherits x's components, and that
> fact was already established in y's private declaration).

And that is why they aren't directly visible to a.c, as a.c can't see
y's full declaration in a.b's private portion.

/Jon
-- 
Jon Anthony
OMI, Belmont, MA 02178
617.484.3383
"Nightmares - Ha!  The way my life's been going lately,
 Who'd notice?"  -- Londo Mollari