An i8 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroI8> is the same size as i8:

assert_eq!(size_of::<Option<core::num::NonZeroI8>>(), size_of::<i8>());

Layout

NonZeroI8 is guaranteed to have the same layout and bit validity as i8 with the exception that 0 is not a valid instance. Option<NonZeroI8> is guaranteed to be compatible with i8, including in FFI.

Thanks to the null pointer optimization, NonZeroI8 and Option<NonZeroI8> are guaranteed to have the same size and alignment:

use std::num::NonZeroI8;

assert_eq!(size_of::<NonZeroI8>(), size_of::<Option<NonZeroI8>>());
assert_eq!(align_of::<NonZeroI8>(), align_of::<Option<NonZeroI8>>());

Compile-time creation

Since both [Option::unwrap()] and [Option::expect()] are const, it is possible to define a new NonZeroI8 at compile time via:

use std::num::NonZeroI8;

const TEN: NonZeroI8 = NonZeroI8::new(10).expect("ten is non-zero");