std: add Duration::as_millis

src/libstd/time/duration.rs

@@ -93,6 +93,16 @@ impl Duration {
     #[stable(feature = "duration", since = "1.3.0")]
     pub fn as_secs(&self) -> u64 { self.secs }
 
+    /// Returns the number of whole milliseconds represented by this duration.
+    ///
+    /// Returns `None` if the operation would overflow.
+    #[unstable(feature = "duration_as_millis", reason = "newly added")]
+    pub fn as_millis(&self) -> Option<u64> {
+        self.secs.checked_mul(MILLIS_PER_SEC).and_then(|millis| {
+            millis.checked_add((self.nanos / NANOS_PER_MILLI) as u64)
+        })
+    }
+
     /// Returns the nanosecond precision represented by this duration.
     ///
     /// This method does **not** return the length of the duration when
@@ -188,6 +198,15 @@ mod tests {
         assert_eq!(Duration::from_millis(1001).as_secs(), 1);
     }
 
+    #[test]
+    fn millis() {
+        assert_eq!(Duration::new(0, 0).as_millis(), Some(0));
+        assert_eq!(Duration::new(0, 5).as_millis(), Some(0));
+        assert_eq!(Duration::from_secs(1).as_millis(), Some(1_000));
+        assert_eq!(Duration::from_millis(999).as_millis(), Some(999));
+        assert_eq!(Duration::from_millis(1001).as_millis(), Some(1001));
+    }
+
     #[test]
     fn nanos() {
         assert_eq!(Duration::new(0, 0).subsec_nanos(), 0);