Implement std::iter::Sum for Duration (#522)

AUTHORS.txt

@@ -22,6 +22,7 @@ Eunchong Yu <kroisse@gmail.com>
 Frans Skarman <frans.skarman@gmail.com>
 Huon Wilson <dbau.pp+github@gmail.com>
 Igor Gnatenko <ignatenko@redhat.com>
+Jake Vossen <jake@vossen.dev>
 Jim Turner <jturner314@gmail.com>
 Jisoo Park <xxxyel@gmail.com>
 Joe Wilm <joe@jwilm.com>

CHANGELOG.md

@@ -17,6 +17,7 @@ Versions with only mechanical changes will be omitted from the following list.
 * Add support for microseconds timestamps serde serialization/deserialization (#304)
 * Fix `DurationRound` is not TZ aware (#495)
 * Implement `DurationRound` for `NaiveDateTime`
+* Implement `std::iter::Sum` for `Duration`
 * Add `DateTime::from_local()` to construct from given local date and time (#572)
 * Add a function that calculates the number of years elapsed between now and a given `Date` or `DateTime` (#557)
 * Correct build for wasm32-unknown-emscripten target (#568)

src/oldtime.rs

@@ -377,6 +377,20 @@ impl Div<i32> for Duration {
     }
 }
 
+#[cfg(any(feature = "std", test))]
+impl<'a> std::iter::Sum<&'a Duration> for Duration {
+    fn sum<I: Iterator<Item = &'a Duration>>(iter: I) -> Duration {
+        iter.fold(Duration::zero(), |acc, x| acc + *x)
+    }
+}
+
+#[cfg(any(feature = "std", test))]
+impl std::iter::Sum<Duration> for Duration {
+    fn sum<I: Iterator<Item = Duration>>(iter: I) -> Duration {
+        iter.fold(Duration::zero(), |acc, x| acc + x)
+    }
+}
+
 impl fmt::Display for Duration {
     /// Format a duration using the [ISO 8601] format
     ///
@@ -634,6 +648,27 @@ mod tests {
         assert_eq!(Duration::seconds(-4) / -3, Duration::nanoseconds(1_333_333_333));
     }
 
+    #[test]
+    fn test_duration_sum() {
+        let duration_list_1 = [Duration::zero(), Duration::seconds(1)];
+        let sum_1: Duration = duration_list_1.iter().sum();
+        assert_eq!(sum_1, Duration::seconds(1));
+
+        let duration_list_2 =
+            [Duration::zero(), Duration::seconds(1), Duration::seconds(6), Duration::seconds(10)];
+        let sum_2: Duration = duration_list_2.iter().sum();
+        assert_eq!(sum_2, Duration::seconds(17));
+
+        let duration_vec = vec![
+            Duration::zero(),
+            Duration::seconds(1),
+            Duration::seconds(6),
+            Duration::seconds(10),
+        ];
+        let sum_3: Duration = duration_vec.into_iter().sum();
+        assert_eq!(sum_3, Duration::seconds(17));
+    }
+
     #[test]
     fn test_duration_fmt() {
         assert_eq!(Duration::zero().to_string(), "PT0S");