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Document Sum::sum returns additive identities for [] #136710

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Feb 9, 2025
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7 changes: 6 additions & 1 deletion library/core/src/iter/traits/iterator.rs
Original file line number Diff line number Diff line change
Expand Up @@ -3493,7 +3493,8 @@ pub trait Iterator {
///
/// Takes each element, adds them together, and returns the result.
///
/// An empty iterator returns the zero value of the type.
/// An empty iterator returns the *additive identity* ("zero") of the type,
/// which is `0` for integers and `-0.0` for floats.
///
/// `sum()` can be used to sum any type implementing [`Sum`][`core::iter::Sum`],
/// including [`Option`][`Option::sum`] and [`Result`][`Result::sum`].
Expand All @@ -3511,6 +3512,10 @@ pub trait Iterator {
/// let sum: i32 = a.iter().sum();
///
/// assert_eq!(sum, 6);
///
/// let b: Vec<f32> = vec![];
/// let sum: f32 = b.iter().sum();
/// assert_eq!(sum, -0.0_f32);
/// ```
#[stable(feature = "iter_arith", since = "1.11.0")]
fn sum<S>(self) -> S
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