An i128 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroI128> is the same size as i128:

assert_eq!(size_of::<Option<core::num::NonZeroI128>>(), size_of::<i128>());

Layout

NonZeroI128 is guaranteed to have the same layout and bit validity as i128 with the exception that 0 is not a valid instance. Option<NonZeroI128> is guaranteed to be compatible with i128, including in FFI.

Thanks to the null pointer optimization, NonZeroI128 and Option<NonZeroI128> are guaranteed to have the same size and alignment:

use std::num::NonZeroI128;

assert_eq!(size_of::<NonZeroI128>(), size_of::<Option<NonZeroI128>>());
assert_eq!(align_of::<NonZeroI128>(), align_of::<Option<NonZeroI128>>());

Compile-time creation

Since both [Option::unwrap()] and [Option::expect()] are const, it is possible to define a new NonZeroI128 at compile time via:

use std::num::NonZeroI128;

const TEN: NonZeroI128 = NonZeroI128::new(10).expect("ten is non-zero");