A u128 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroU128> is the same size as u128:

assert_eq!(size_of::<Option<core::num::NonZeroU128>>(), size_of::<u128>());

Layout

NonZeroU128 is guaranteed to have the same layout and bit validity as u128 with the exception that 0 is not a valid instance. Option<NonZeroU128> is guaranteed to be compatible with u128, including in FFI.

Thanks to the null pointer optimization, NonZeroU128 and Option<NonZeroU128> are guaranteed to have the same size and alignment:

use std::num::NonZeroU128;

assert_eq!(size_of::<NonZeroU128>(), size_of::<Option<NonZeroU128>>());
assert_eq!(align_of::<NonZeroU128>(), align_of::<Option<NonZeroU128>>());

Compile-time creation

Since both [Option::unwrap()] and [Option::expect()] are const, it is possible to define a new NonZeroU128 at compile time via:

use std::num::NonZeroU128;

const TEN: NonZeroU128 = NonZeroU128::new(10).expect("ten is non-zero");