error[E0596]: cannot borrow `*x` as mutable, as it is behind a `&` reference --> $DIR/borrowck-object-mutability.rs:8:5 | LL | x.borrowed_mut(); | ^ `x` is a `&` reference, so the data it refers to cannot be borrowed as mutable | help: consider changing this to be a mutable reference | LL | fn borrowed_receiver(x: &mut dyn Foo) { | +++ error[E0596]: cannot borrow `*x` as mutable, as `x` is not declared as mutable --> $DIR/borrowck-object-mutability.rs:18:5 | LL | x.borrowed_mut(); | ^ cannot borrow as mutable | help: consider changing this to be mutable | LL | fn owned_receiver(mut x: Box) { | +++ error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0596`.