Specialize Vec::extend to Vec::extend_from_slice

diff --git a/src/libcollections/vec.rs b/src/libcollections/vec.rs
index 54fd19dbe3058cd7a310ba34077b749fb82634bb..4a727adb797e01b5ea304264e7d866950a040106 100644 (file)
--- a/src/libcollections/vec.rs
+++ b/src/libcollections/vec.rs
@@ -1571,7 +1571,24 @@ fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
 #[stable(feature = "extend_ref", since = "1.2.0")]
 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
-        self.extend(iter.into_iter().cloned());
+        <I as SpecExtendVec<T>>::extend_vec(iter, self);
+    }
+}
+
+// helper trait for specialization of Vec's Extend impl
+trait SpecExtendVec<T> {
+    fn extend_vec(self, vec: &mut Vec<T>);
+}
+
+impl <'a, T: 'a + Copy, I: IntoIterator<Item=&'a T>> SpecExtendVec<T> for I {
+    default fn extend_vec(self, vec: &mut Vec<T>) {
+        vec.extend(self.into_iter().cloned());
+    }
+}
+
+impl<'a, T: Copy> SpecExtendVec<T> for &'a [T] {
+    fn extend_vec(self, vec: &mut Vec<T>) {
+        vec.extend_from_slice(self);
     }
 }