Implement RFC 839 for String

Author: jooert

src/libcollections/string.rs

@@ -793,6 +793,13 @@ impl Extend<char> for String {
     }
 }
 
+#[unstable(feature = "extend_ref", reason = "recently added")]
+impl<'a> Extend<&'a char> for String {
+    fn extend<I: IntoIterator<Item=&'a char>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().cloned());
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Extend<&'a str> for String {
     fn extend<I: IntoIterator<Item=&'a str>>(&mut self, iterable: I) {

src/libcollectionstest/string.rs

@@ -365,6 +365,14 @@ fn test_drain() {
     assert_eq!(t, "");
 }
 
+#[test]
+fn test_extend_ref() {
+    let mut a = "foo".to_string();
+    a.extend(&['b', 'a', 'r']);
+
+    assert_eq!(&a, "foobar");
+}
+
 #[bench]
 fn bench_with_capacity(b: &mut Bencher) {
     b.iter(|| {