error[E0499]: cannot borrow `xs` as mutable more than once at a time --> $DIR/vec-mut-iter-borrow.rs:5:9 | LL | for x in &mut xs { | ------- | | | first mutable borrow occurs here | first borrow later used here LL | xs.push(1) | ^^ second mutable borrow occurs here error: aborting due to previous error For more information about this error, try `rustc --explain E0499`.