error[E0507]: cannot move out of dereference of `Ref<'_, TheDarkKnight>`
  --> $DIR/E0507.rs:12:5
   |
LL |     x.borrow().nothing_is_true();
   |     ^^^^^^^^^^^-----------------
   |     |          |
   |     |          value moved due to this method call
   |     move occurs because value has type `TheDarkKnight`, which does not implement the `Copy` trait
   |
note: `TheDarkKnight::nothing_is_true` takes ownership of the receiver `self`, which moves value
  --> $DIR/E0507.rs:6:24
   |
LL |     fn nothing_is_true(self) {}
   |                        ^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0507`.