https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58040
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |INVALID
--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Matt Whitlock from comment #8)
> As you can see, it is possible to call all four member functions directly
> using their qualified names,
Yes, because the /name/ of the function is accessible in Derived, because the
using-declarations delcare them as publicly accessible members of Derived.
> but it is not possible to assign the addresses
> of the members from the protected base into variables whose type is pointer
> to member function of the derived class,
Because that's not the type of the function, and [conv.mem] p2 says you can't
convert them from void (ProtectedBase::*)() to void (Derived::*)() because that
base class is not accessible.
[conv.mem] p2 says:
A prvalue of type “pointer to member of B of type cv T”, where B is a class
type, can be converted to a prvalue of type “pointer to member of D of type cv
T”, where D is a complete class derived (11.7) from B. If B is an inaccessible
(11.8), ambiguous (6.5.2), or virtual (11.7.2) base class of D, or a base class
of a virtual base class of D, a program that necessitates this conversion is
ill-formed.
> nor is it possible to call the
> members of the protected base indirectly through pointers to member function
> of the derived class.
You are not calling them by name here, so the using-declaration isn't relevant.
You are trying to invoke a member of the protect base through the derived type,
which requires converting &d to a ProtectedBase*, which is not an allowed
conversion.
Not a bug, this is how C++ works.
