An i32 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroI32> is the same size as i32:

assert_eq!(size_of::<Option<core::num::NonZeroI32>>(), size_of::<i32>());

Layout

NonZeroI32 is guaranteed to have the same layout and bit validity as i32 with the exception that 0 is not a valid instance. Option<NonZeroI32> is guaranteed to be compatible with i32, including in FFI.

Thanks to the null pointer optimization, NonZeroI32 and Option<NonZeroI32> are guaranteed to have the same size and alignment:

use std::num::NonZeroI32;

assert_eq!(size_of::<NonZeroI32>(), size_of::<Option<NonZeroI32>>());
assert_eq!(align_of::<NonZeroI32>(), align_of::<Option<NonZeroI32>>());

Compile-time creation

Since both [Option::unwrap()] and [Option::expect()] are const, it is possible to define a new NonZeroI32 at compile time via:

use std::num::NonZeroI32;

const TEN: NonZeroI32 = NonZeroI32::new(10).expect("ten is non-zero");