Implement RFC 839 for BTreeSet

Author: jooert

src/libcollections/btree/set.rs

@@ -509,6 +509,13 @@ impl<T: Ord> Extend<T> for BTreeSet<T> {
     }
 }
 
+#[unstable(feature = "extend_ref", reason = "recently added")]
+impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BTreeSet<T> {
+    fn extend<I: IntoIterator<Item=&'a T>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().cloned());
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord> Default for BTreeSet<T> {
     #[stable(feature = "rust1", since = "1.0.0")]

src/libcollectionstest/btree/set.rs

@@ -184,3 +184,31 @@ fn test_show() {
     assert_eq!(set_str, "{1, 2}");
     assert_eq!(format!("{:?}", empty), "{}");
 }
+
+#[test]
+fn test_extend_ref() {
+    let mut a = BTreeSet::new();
+    a.insert(1);
+
+    a.extend(&[2, 3, 4]);
+
+    assert_eq!(a.len(), 4);
+    assert!(a.contains(&1));
+    assert!(a.contains(&2));
+    assert!(a.contains(&3));
+    assert!(a.contains(&4));
+
+    let mut b = BTreeSet::new();
+    b.insert(5);
+    b.insert(6);
+
+    a.extend(&b);
+
+    assert_eq!(a.len(), 6);
+    assert!(a.contains(&1));
+    assert!(a.contains(&2));
+    assert!(a.contains(&3));
+    assert!(a.contains(&4));
+    assert!(a.contains(&5));
+    assert!(a.contains(&6));
+}