NonZeroU8 in std::num - Rust (original) (raw)

Type Alias NonZeroU8

1.28.0 · Source

pub type NonZeroU8 = NonZero<u8>;

Expand description

A u8 that is known not to equal zero.

This enables some memory layout optimization. For example, Option<NonZeroU8> is the same size as u8:

use std::mem::size_of;
assert_eq!(size_of::<Option<core::num::NonZeroU8>>(), size_of::<u8>());

§Layout

NonZeroU8 is guaranteed to have the same layout and bit validity as u8with the exception that 0 is not a valid instance.Option<NonZeroU8> is guaranteed to be compatible with u8, including in FFI.

Thanks to the null pointer optimization,NonZeroU8 and Option<NonZeroU8>are guaranteed to have the same size and alignment:

use std::num::NonZeroU8;

assert_eq!(size_of::<NonZeroU8>(), size_of::<Option<NonZeroU8>>());
assert_eq!(align_of::<NonZeroU8>(), align_of::<Option<NonZeroU8>>());

struct NonZeroU8(/* private fields */);