# Error code E0507

A borrowed value was moved out.

Erroneous code example:

    use std::cell::RefCell;

    struct TheDarkKnight;

    impl TheDarkKnight {
        fn nothing_is_true(self) {}
    }

    fn main() {
        let x = RefCell::new(TheDarkKnight);

        x.borrow().nothing_is_true(); // error: cannot move out of borrowed content
    }

Here, the `nothing_is_true` method takes the ownership of `self`. However, `self` cannot be moved because `.borrow()` only provides an `&TheDarkKnight`, which is a borrow of the content owned by the `RefCell`. To fix this error, you have three choices:

- Try to avoid moving the variable.
- Somehow reclaim the ownership.
- Implement the `Copy` trait on the type.

This can also happen when using a type implementing `Fn` or `FnMut`, as neither allows moving out of them (they usually represent closures which can be called more than once). Much of the text following applies equally well to non-`FnOnce` closure bodies.

Examples:

    use std::cell::RefCell;

    struct TheDarkKnight;

    impl TheDarkKnight {
        fn nothing_is_true(&self) {} // First case, we don't take ownership
    }

    fn main() {
        let x = RefCell::new(TheDarkKnight);

        x.borrow().nothing_is_true(); // ok!
    }

Or:

    use std::cell::RefCell;

    struct TheDarkKnight;

    impl TheDarkKnight {
        fn nothing_is_true(self) {}
    }

    fn main() {
        let x = RefCell::new(TheDarkKnight);
        let x = x.into_inner(); // we get back ownership

        x.nothing_is_true(); // ok!
    }

Or:

    use std::cell::RefCell;

    #[derive(Clone, Copy)] // we implement the Copy trait
    struct TheDarkKnight;

    impl TheDarkKnight {
        fn nothing_is_true(self) {}
    }

    fn main() {
        let x = RefCell::new(TheDarkKnight);

        x.borrow().nothing_is_true(); // ok!
    }

Moving a member out of a mutably borrowed struct will also cause E0507 error:

    struct TheDarkKnight;

    impl TheDarkKnight {
        fn nothing_is_true(self) {}
    }

    struct Batcave {
        knight: TheDarkKnight
    }

    fn main() {
        let mut cave = Batcave {
            knight: TheDarkKnight
        };
        let borrowed = &mut cave;

        borrowed.knight.nothing_is_true(); // E0507
    }

It is fine only if you put something back. `mem::replace` can be used for that:

    #![allow(unused)]
    fn main() {
    struct TheDarkKnight;
    impl TheDarkKnight { fn nothing_is_true(self) {} }
    struct Batcave { knight: TheDarkKnight }
    use std::mem;

    let mut cave = Batcave {
        knight: TheDarkKnight
    };
    let borrowed = &mut cave;

    mem::replace(&mut borrowed.knight, TheDarkKnight).nothing_is_true(); // ok!
    }

For more information on Rust's ownership system, take a look at the References & Borrowing section of the Book.