error[E0499]: cannot borrow `thing` as mutable more than once at a time --> $DIR/retain-resume-ref.rs:23:25 | LL | gen.as_mut().resume(&mut thing); | ---------- first mutable borrow occurs here LL | gen.as_mut().resume(&mut thing); | ------ ^^^^^^^^^^ second mutable borrow occurs here | | | first borrow later used by call error: aborting due to previous error For more information about this error, try `rustc --explain E0499`.