NonZeroUsize in core::num - Rust
Description: A `usize` that is known not to equal zero.

# Type Alias NonZeroUsize

1.28.0 · Source

    pub type NonZeroUsize = NonZero<usize>;

Expand description

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`:

    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 */);