[Bug libstdc++/55713] New: std::tuple<ElementType> incorrectly is convertible to "ElementType" when it is an empty class

[schaub.johannes at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55713

             Bug #: 55713
           Summary: std::tuple<ElementType> incorrectly is convertible to
                    "ElementType" when it is an empty class
    Classification: Unclassified
           Product: gcc
           Version: 4.7.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: schaub.johannes@googlemail.com


This code cannot be compiled with libstdc++

struct A {};
void f(A);

struct B { B(std::tuple<A>); };
void f(B);

int main() {
  f(std::make_tuple(A()));
}

GCC shouts

  "error: 'A' is an inaccessible base of 'tuple<A>'"

Libstdc++ should not make "std::tuple<EmptyClass>" derive from the empty class
directly.