An i64 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroI64> is the same size as i64:

assert_eq!(size_of::<Option<core::num::NonZeroI64>>(), size_of::<i64>());

Layout

NonZeroI64 is guaranteed to have the same layout and bit validity as i64 with the exception that 0 is not a valid instance. Option<NonZeroI64> is guaranteed to be compatible with i64, including in FFI.

Thanks to the null pointer optimization, NonZeroI64 and Option<NonZeroI64> are guaranteed to have the same size and alignment:

use std::num::NonZeroI64;

assert_eq!(size_of::<NonZeroI64>(), size_of::<Option<NonZeroI64>>());
assert_eq!(align_of::<NonZeroI64>(), align_of::<Option<NonZeroI64>>());

Compile-time creation

Since both [Option::unwrap()] and [Option::expect()] are const, it is possible to define a new NonZeroI64 at compile time via:

use std::num::NonZeroI64;

const TEN: NonZeroI64 = NonZeroI64::new(10).expect("ten is non-zero");