How to convert a slice into an array reference?

Question

I have an &[u8] and would like to turn it into an &[u8; 3] without copying. It should reference the original array. How can I do this?

Answer 1

Just to re-emphasize, this can't be done without unsafe code because you don't know until runtime that the slice has three elements in it.

fn slice_to_arr3(slice: &[T]) -> Option<&[T; 3]> {
    if slice.len() == 3 {
        Some(unsafe { &*(slice as *const [T] as *const [T; 3]) })
    } else {
        None
    }
}

This can't be generic over the length of the array until const generics are implemented.