NonZeroIsize in std::num - Rust
Description: An `isize` that is known not to equal zero.

## NonZeroIsize

# Type Alias NonZeroIsize

1.34.0 · Source

    pub type NonZeroIsize = NonZero<isize>;

Expand description

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`:

    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>>());

## §Compile-time creation

Since both `Option::unwrap()` and `Option::expect()` are `const`, it is possible to define a new `NonZeroIsize` at compile time via:

    use std::num::NonZeroIsize;

    const TEN: NonZeroIsize = NonZeroIsize::new(10).expect("ten is non-zero");

## Aliased Type§

    pub struct NonZeroIsize(/* private fields */);