A u8 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroU8> is the same size as u8:

assert_eq!(size_of::<Option<core::num::NonZeroU8>>(), size_of::<u8>());

Layout

NonZeroU8 is guaranteed to have the same layout and bit validity as u8 with the exception that 0 is not a valid instance. Option<NonZeroU8> is guaranteed to be compatible with u8, including in FFI.

Thanks to the null pointer optimization, NonZeroU8 and Option<NonZeroU8> are guaranteed to have the same size and alignment:

use std::num::NonZeroU8;

assert_eq!(size_of::<NonZeroU8>(), size_of::<Option<NonZeroU8>>());
assert_eq!(align_of::<NonZeroU8>(), align_of::<Option<NonZeroU8>>());

Compile-time creation

Since both [Option::unwrap()] and [Option::expect()] are const, it is possible to define a new NonZeroU8 at compile time via:

use std::num::NonZeroU8;

const TEN: NonZeroU8 = NonZeroU8::new(10).expect("ten is non-zero");