4 fail_compilation/ice14130.d(10): Error: undefined identifier `Undef`
5 fail_compilation/ice14130.d(14): Error: template ice14130.foo cannot deduce function from argument types !()(int), candidates are:
6 fail_compilation/ice14130.d(10): ice14130.foo(R, F = Undef)(R r, F s = 0)
10 F foo(R, F = Undef)(R r, F s = 0) {}