error[E0373]: closure may outlive the current function, but it borrows `books`, which is owned by the current function --> $DIR/borrowck-escaping-closure-error-2.rs:11:14 | LL | Box::new(|| books.push(4)) | ^^ ----- `books` is borrowed here | | | may outlive borrowed value `books` | note: closure is returned here --> $DIR/borrowck-escaping-closure-error-2.rs:11:5 | LL | Box::new(|| books.push(4)) | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: to force the closure to take ownership of `books` (and any other referenced variables), use the `move` keyword | LL | Box::new(move || books.push(4)) | ++++ error: aborting due to previous error For more information about this error, try `rustc --explain E0373`.