error[E0596]: cannot borrow `*self.s` as mutable, as it is behind a `&` reference --> $DIR/issue-38147-3.rs:7:9 | LL | self.s.push('x'); | ^^^^^^^^^^^^^^^^ cannot borrow as mutable | help: consider changing this to be mutable | LL | s: &'a mut String | +++ error: aborting due to previous error For more information about this error, try `rustc --explain E0596`.