impl Default for RepeatN

library/core/src/iter/sources/repeat_n.rs

@@ -133,6 +133,15 @@ impl<A> Drop for RepeatN<A> {
  }
 }
 
+/// Creates an empty iterator, like [`repeat_n(value, 0)`][`repeat_n`]
+/// but without needing any such value at hand.
+#[stable(feature = "iter_repeat_n_default", since = "CURRENT_RUSTC_VERSION")]
+impl<A> Default for RepeatN<A> {
+ fn default() -> Self {
+ RepeatN { count: 0, element: MaybeUninit::uninit() }
+ }
+}
+
 #[stable(feature = "iter_repeat_n", since = "1.82.0")]
 impl<A: Clone> Iterator for RepeatN<A> {
  type Item = A;

library/coretests/tests/iter/sources.rs

@@ -180,3 +180,19 @@ fn test_repeat_n_soundness() {
  let _z = y;
  assert_eq!(0, *x);
 }
+
+#[test]
+fn test_repeat_n_default() {
+ #[derive(Clone)]
+ pub struct PanicOnDrop;
+
+ impl Drop for PanicOnDrop {
+ fn drop(&mut self) {
+ unreachable!()
+ }
+ }
+
+ // The default is an empty iterator, so there's never any item to drop.
+ let iter = RepeatN::<PanicOnDrop>::default();
+ assert_eq!(iter.count(), 0);
+}