Type Alias NonZeroIsize

pub type NonZeroIsize = NonZero<isize>;

An isize that is known not to equal zero.

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

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

Layout

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

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

use std::num::NonZeroIsize;

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

Aliased Type

struct NonZeroIsize(/* private fields */);