Add core::iter::once_with

2 files changed, 18 insertions, 0 deletions

diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index cf19851c17b..b62f55b2cd0 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -1907,6 +1907,23 @@ fn test_once() {
 }
 
 #[test]
+fn test_once_with() {
+    let mut count = 0;
+    let mut it = once_with(|| {
+        count += 1;
+        42
+    });
+
+    assert_eq!(count, 0);
+    assert_eq!(it.next(), Some(42));
+    assert_eq!(count, 1);
+    assert_eq!(it.next(), None);
+    assert_eq!(count, 1);
+    assert_eq!(it.next(), None);
+    assert_eq!(count, 1);
+}
+
+#[test]
 fn test_empty() {
     let mut it = empty::<i32>();
     assert_eq!(it.next(), None);
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 72846daf16a..a9b8decfd02 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -12,6 +12,7 @@
 #![feature(hashmap_internals)]
 #![feature(iter_copied)]
 #![feature(iter_nth_back)]
+#![feature(iter_once_with)]
 #![feature(iter_unfold)]
 #![feature(pattern)]
 #![feature(range_is_empty)]