error[E0308]: mismatched types --> $DIR/mut-cross-borrowing.rs:7:7 | LL | f(x) | - ^ expected `&mut isize`, found `Box<{integer}>` | | | arguments to this function are incorrect | = note: expected mutable reference `&mut isize` found struct `Box<{integer}>` note: function defined here --> $DIR/mut-cross-borrowing.rs:1:4 | LL | fn f(_: &mut isize) {} | ^ ------------- help: consider mutably borrowing here | LL | f(&mut x) | ++++ error: aborting due to previous error For more information about this error, try `rustc --explain E0308`.