Type Alias NonZeroU64

pub type NonZeroU64 = NonZero<u64>;

A u64 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroU64> is the same size as u64:

use std::mem::size_of;
assert_eq!(size_of::<Option<core::num::NonZeroU64>>(), size_of::<u64>());

Layout

NonZeroU64 is guaranteed to have the same layout and bit validity as u64 with the exception that 0 is not a valid instance. Option<NonZeroU64> is guaranteed to be compatible with u64, including in FFI.

Thanks to the null pointer optimization, NonZeroU64 and Option<NonZeroU64> are guaranteed to have the same size and alignment:

use std::num::NonZeroU64;

assert_eq!(size_of::<NonZeroU64>(), size_of::<Option<NonZeroU64>>());
assert_eq!(align_of::<NonZeroU64>(), align_of::<Option<NonZeroU64>>());

Aliased Type

struct NonZeroU64(/* private fields */);