//@ In part 13, we talked about types that are marked `Send` and thus can be moved to another thread. However, we did *not*
//@ talk about the question whether a reference is `Send`. For `&mut T`, the answer is: It is `Send` whenever `T` is send.
//@ `&mut` allows moving values back and forth, it is even possible to [`swap`](https://doc.rust-lang.org/stable/std/mem/fn.swap.html)
//@ In part 13, we talked about types that are marked `Send` and thus can be moved to another thread. However, we did *not*
//@ talk about the question whether a reference is `Send`. For `&mut T`, the answer is: It is `Send` whenever `T` is send.
//@ `&mut` allows moving values back and forth, it is even possible to [`swap`](https://doc.rust-lang.org/stable/std/mem/fn.swap.html)