Auto merge of #81152 - lzutao:intersperse_fold, r=m-ou-se

[rust.git] / library / core / tests / iter.rs

diff --git a/library/core/tests/iter.rs b/library/core/tests/iter.rs
index fa259e68a4370f0eea42c56c4d2d464ae6064ff4..78b4d1acaf5cd3119d619b79dab7a2bbdf749136 100644 (file)
--- a/library/core/tests/iter.rs
+++ b/library/core/tests/iter.rs
@@ -3577,6 +3577,18 @@ fn test_intersperse_fold() {
         acc
     });
     assert_eq!(v.as_slice(), [9, 2, 9, 3]);
+
+    struct NoneAtStart(i32); // Produces: None, Some(2), Some(3), None, ...
+    impl Iterator for NoneAtStart {
+        type Item = i32;
+        fn next(&mut self) -> Option<i32> {
+            self.0 += 1;
+            Some(self.0).filter(|i| i % 3 != 1)
+        }
+    }
+
+    let v = NoneAtStart(0).intersperse(1000).fold(0, |a, b| a + b);
+    assert_eq!(v, 0);
 }
 
 #[test]