[Issue 4542] [tdpl] TDPL NVI example results in linker error

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=4542

--- Comment #19 from Simon Naarmann <eiderdaus at gmail.com> ---
(In reply to RazvanN from comment #17)
> (In reply to Simon Naarmann from comment #16)
> >     interface IA {
> >         package void f();
> >     }
> >     void main() {
> >         IA a;
> >         a.f();
> >     }
> 
> I don't understand what you expect to happen in this case. You are calling f
> which does not have a body.

Indeed, if I don't inherit from IA, getting a linker error here is correct in
this small example.

My best guess of why I posted that reply 6 years ago: It was a faulty reduction
of the original bug, but I mistook it for a correct reduction. I dustmited for
the linker error and didn't pay attention to whether the reduced linker error
arose with or without a class that tried to implement the private/package
virtual function.

I agree to treat this as a mistake in TDPL and to forbid overriding
private/package methods, as the spec says. Nowadays, OP's example also produces
a proper compiler error, much better than the original linker error:

    tdpl_private_virtual.d(18): Error: function
`tdpl_private_virtual.CardBoardBox.transmogrify` `private` method is not
virtual and cannot override
    tdpl_private_virtual.d(23): Error: function
`tdpl_private_virtual.CardBoardBox.untransmogrify` `private` method is not
virtual and cannot override

With this good error already in place, I'm happy with the resolution as
wontfix.

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