A [u8;32] doesn't work with Pin. Pin only works when you wrap it around a pointer type. From the documentation on Unpin: > Since Rust itself has no notion of i

A [u8;32] doesn't work with Pin. Pin only works when you wrap it around a pointer type. From the documentation on Unpin: > Since Rust itself has no notion of immovable types, and will consider moves to always be safe, this trait cannot prevent types from moving by itself. From the documentation on std::pin: > In order to prevent objects from moving, they must be pinned by wrapping a pointer to the data in the Pin type. A pointer wrapped in a Pin is otherwise equivalent to its normal version, e.g. Pin<Box<T>> and Box<T> work the same way except that the first is pinning the value of T in place. > First of all, these are pointer types because pinned data mustn't be passed around by value (that would change its location in memory). … Looking at Pin itself, it appears that it works by only implementing DerefMut if its target is Unpin, thus preventing you from mutating (and therefore swapping/replacing) the data unless the data supports Unpin. But beyond that, it also only implements Deref and DerefMut if its wrapped type itself implements Deref/DerefMut, which means using Pin around a non-pointer basically prevents you from accessing the wrapped data.