NonZeroU32 in std::num - Rust (original) (raw)

Type Alias NonZeroU32

1.28.0 · Source

pub type NonZeroU32 = NonZero<u32>;

Expand description

A u32 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroU32> is the same size as u32:

use std::mem::size_of;
assert_eq!(size_of::<Option<core::num::NonZeroU32>>(), size_of::<u32>());

§Layout

NonZeroU32 is guaranteed to have the same layout and bit validity as u32with the exception that 0 is not a valid instance.Option<NonZeroU32> is guaranteed to be compatible with u32, including in FFI.

Thanks to the null pointer optimization,NonZeroU32 and Option<NonZeroU32>are guaranteed to have the same size and alignment:

use std::num::NonZeroU32;

assert_eq!(size_of::<NonZeroU32>(), size_of::<Option<NonZeroU32>>());
assert_eq!(align_of::<NonZeroU32>(), align_of::<Option<NonZeroU32>>());

struct NonZeroU32(/* private fields */);