borrowck-escaping-closure-error-2.stderr

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:21:14
   |
21 |     Box::new(|| books.push(4))
   |              ^^ ----- `books` is borrowed here
   |              |
   |              may outlive borrowed value `books`
help: to force the closure to take ownership of `books` (and any other referenced variables), use the `move` keyword
   |
21 |     Box::new(move || books.push(4))
   |              ^^^^^^^

error: aborting due to previous error

If you want more information on this error, try using "rustc --explain E0373"