Implement RFC 839 for BTreeMap

Author: jooert

src/libcollections/btree/map.rs

@@ -879,6 +879,13 @@ impl<K: Ord, V> Extend<(K, V)> for BTreeMap<K, V> {
     }
 }
 
+#[unstable(feature = "extend_ref", reason = "recently added")]
+impl<'a, K: Ord + Copy, V: Copy> Extend<(&'a K, &'a V)> for BTreeMap<K, V> {
+    fn extend<I: IntoIterator<Item=(&'a K, &'a V)>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K: Hash, V: Hash> Hash for BTreeMap<K, V> {
     fn hash<H: Hasher>(&self, state: &mut H) {

src/libcollectionstest/btree/map.rs

@@ -249,6 +249,22 @@ fn test_entry(){
     assert_eq!(map.len(), 6);
 }
 
+#[test]
+fn test_extend_ref() {
+    let mut a = BTreeMap::new();
+    a.insert(1, "one");
+    let mut b = BTreeMap::new();
+    b.insert(2, "two");
+    b.insert(3, "three");
+
+    a.extend(&b);
+
+    assert_eq!(a.len(), 3);
+    assert_eq!(a[&1], "one");
+    assert_eq!(a[&2], "two");
+    assert_eq!(a[&3], "three");
+}
+
 mod bench {
     use std::collections::BTreeMap;
     use std::__rand::{Rng, thread_rng};