Type Alias NonZeroUsize

pub type NonZeroUsize = NonZero<usize>;

A usize that is known not to equal zero.

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

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

Layout

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

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

use std::num::NonZeroUsize;

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

Aliased Type

struct NonZeroUsize(/* private fields */);