A u32 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroU32> is the same size as u32:

assert_eq!(size_of::<Option<core::num::NonZeroU32>>(), size_of::<u32>());

Layout

NonZeroU32 is guaranteed to have the same layout and bit validity as u32 with the exception that 0 is not a valid instance. Option<NonZeroU32> is guaranteed to be compatible with u32, including in FFI.

Thanks to the null pointer optimization, NonZeroU32 and Option<NonZeroU32> are guaranteed to have the same size and alignment:

use std::num::NonZeroU32;

assert_eq!(size_of::<NonZeroU32>(), size_of::<Option<NonZeroU32>>());
assert_eq!(align_of::<NonZeroU32>(), align_of::<Option<NonZeroU32>>());

Compile-time creation

Since both [Option::unwrap()] and [Option::expect()] are const, it is possible to define a new NonZeroU32 at compile time via:

use std::num::NonZeroU32;

const TEN: NonZeroU32 = NonZeroU32::new(10).expect("ten is non-zero");