all_is_bytes

Function cast

Source 
pub unsafe fn cast<T>(x: &T) -> &[MaybeUninit<u8>]
where
    T: ?Sized,
Expand description

Reinterprets as a byte slice.

Returns &[MaybeUninit<u8>] rather than &[u8] as it is undefined behavior to read padding bytes. If the type does not contain any padding, it is safe to cast it to &[u8] yourself.

§Safety

The type must not have interior mutability.

In other words, the type cannot contain Cell, UnsafeCell, and the like.

§Why?

Aliasing. See here:

let cell = Cell::new(1u8);
let raw = unsafe { all_is_bytes::cast(&cell) };
cell.set(0u8); // Erm... well that just happened...
assert_eq!(cell.get(), unsafe { raw[0].assume_init() }); // Uh oh!

This causes undefined behavior.