2 // Tests that unary structs can be mutably borrowed.
7 fn next(&mut self) -> Option<U>;
9 impl T<isize> for Empty {
10 fn next(&mut self) -> Option<isize> { None }
13 fn do_something_with(a : &mut dyn T<isize>) {
14 println!("{:?}", a.next())
18 do_something_with(&mut Empty);