error[E0596]: cannot borrow `*self.s` as mutable, as it is behind a `&` reference --> $DIR/issue-38147-1.rs:17:9 | LL | self.s.push('x'); | ^^^^^^^^^^^^^^^^ `self` 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 f(&mut self) { | ~~~~~~~~~ error: aborting due to previous error For more information about this error, try `rustc --explain E0596`.