diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs index 83c7e8977e9..182ef241c45 100644 --- a/library/core/src/iter/traits/iterator.rs +++ b/library/core/src/iter/traits/iterator.rs @@ -3475,8 +3475,10 @@ fn compare(mut cmp: F) -> impl FnMut(X, Y) -> ControlFlow } } - /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those - /// of another. + /// [Lexicographically](Ord#lexicographical-comparison) compares the [`PartialOrd`] elements of + /// this [`Iterator`] with those of another. The comparison works like short-circuit + /// evaluation, returning a result without comparing the remaining elements. + /// As soon as an order can be determined, the evaluation stops and a result is returned. /// /// # Examples /// @@ -3486,9 +3488,25 @@ fn compare(mut cmp: F) -> impl FnMut(X, Y) -> ControlFlow /// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal)); /// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less)); /// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater)); + /// ``` /// + /// For floating-point numbers, NaN does not have a total order and will result + /// in `None` when compared: + /// + /// ``` /// assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None); /// ``` + /// + /// The results are determined by the order of evaluation. + /// + /// ``` + /// use std::cmp::Ordering; + /// + /// assert_eq!([1.0, f64::NAN].iter().partial_cmp([2.0, f64::NAN].iter()), Some(Ordering::Less)); + /// assert_eq!([2.0, f64::NAN].iter().partial_cmp([1.0, f64::NAN].iter()), Some(Ordering::Greater)); + /// assert_eq!([f64::NAN, 1.0].iter().partial_cmp([f64::NAN, 2.0].iter()), None); + /// ``` + /// #[stable(feature = "iter_order", since = "1.5.0")] fn partial_cmp(self, other: I) -> Option where