diff options
| -rw-r--r-- | library/core/src/num/nonzero.rs | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/library/core/src/num/nonzero.rs b/library/core/src/num/nonzero.rs index 7d60686597a..bda691b16d4 100644 --- a/library/core/src/num/nonzero.rs +++ b/library/core/src/num/nonzero.rs @@ -171,6 +171,39 @@ macro_rules! nonzero_integer { } } + /// Converts a primitive mutable reference to a non-zero mutable reference + /// without checking whether the referenced value is non-zero. + /// This results in undefined behavior if `*n` is zero. + /// + /// # Safety + /// The referenced value must not be currently zero. + #[unstable(feature = "nonzero_from_mut", issue = "106290")] + #[must_use] + #[inline] + pub unsafe fn from_mut_unchecked(n: &mut $Int) -> &mut Self { + // SAFETY: Self is repr(transparent), and the value is assumed to be non-zero. + unsafe { + let n_alias = &mut *n; + core::intrinsics::assert_unsafe_precondition!( + concat!(stringify!($Ty), "::from_mut_unchecked requires the argument to dereference as non-zero"), + (n_alias: &mut $Int) => *n_alias != 0 + ); + &mut *(n as *mut $Int as *mut Self) + } + } + + /// Converts a primitive mutable reference to a non-zero mutable reference + /// if the referenced integer is not zero. + #[unstable(feature = "nonzero_from_mut", issue = "106290")] + #[must_use] + #[inline] + pub fn from_mut(n: &mut $Int) -> Option<&mut Self> { + // SAFETY: Self is repr(transparent), and the value is non-zero. + // As long as the returned reference is alive, + // the user cannot `*n = 0` directly. + (*n != 0).then(|| unsafe { &mut *(n as *mut $Int as *mut Self) }) + } + /// Returns the value as a primitive type. #[$stability] #[inline] |