Implement DerefMut for String

`&mut str` is rarely useful, but it is for e.g.
`AsciiExt::make_ascii_lowercase`.

diff --git a/src/libcollections/string.rs b/src/libcollections/string.rs
index ef1d9b08b4a9a6d4b5b5328c5529f9c71bd4db62..491b7a6dd919bb53937ddb2086baae15cdec6722 100644 (file)
--- a/src/libcollections/string.rs
+++ b/src/libcollections/string.rs
@@ -989,6 +989,14 @@ fn deref(&self) -> &str {
     }
 }
 
+#[stable(feature = "derefmut_for_string", since = "1.2.0")]
+impl ops::DerefMut for String {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut str {
+        unsafe { mem::transmute(&mut self.vec[..]) }
+    }
+}
+
 /// Wrapper type providing a `&String` reference via `Deref`.
 #[unstable(feature = "collections")]
 #[deprecated(since = "1.2.0",