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Rollup merge of #146924 - cptpiepmatz:doc-nonzero-const-creation, r=joboet

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Add doc for `NonZero*` const creation

I ran into trouble using `NonZero*` values because I didn’t see any clear way to create them at compile time. At first I ended up using `NonZero*::new_unchecked` a lot, until I realized that `Option::unwrap` and `Option::expect` are `const` and can be used in a `const` context. With that, you can create non-zero values at compile time safely, without touching `unsafe`. This wasn’t obvious to me and my peers who’ve been using Rust for a while, so I thought adding a note to the docs would make it easier for others to discover.

If this should be worded differently or placed in another location, we can do that. I just want to make this more obvious.
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Matthias Krüger 2025-09-25 18:15:10 +02:00 committed by GitHub
commit 781f71a6fe
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library/core/src/num/nonzero.rs
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@ -548,6 +548,18 @@ macro_rules! nonzero_integer {
#[doc = concat!("assert_eq!(align_of::<", stringify!($Ty), ">(), align_of::<Option<", stringify!($Ty), ">>());")]
/// ```
///
/// # Compile-time creation
///
/// Since both [`Option::unwrap()`] and [`Option::expect()`] are `const`, it is possible to
/// define a new
#[doc = concat!("`", stringify!($Ty), "`")]
/// at compile time via:
/// ```
#[doc = concat!("use std::num::", stringify!($Ty), ";")]
///
#[doc = concat!("const TEN: ", stringify!($Ty), " = ", stringify!($Ty) , r#"::new(10).expect("ten is non-zero");"#)]
/// ```
///
/// [null pointer optimization]: crate::option#representation
#[$stability]
pub type $Ty = NonZero<$Int>;