Make mut_last return Option instead of failing on empty vector (and add a test for mut_last)

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax/opt_vec.rs b/src/libsyntax/opt_vec.rs
index ce3042cb9cd..c575e170bef 100644
--- a/src/libsyntax/opt_vec.rs
+++ b/src/libsyntax/opt_vec.rs
@@ -62,10 +62,10 @@ impl<T> OptVec<T> {
         }
     }
 
-    pub fn mut_last<'a>(&'a mut self) -> &'a mut T {
+    pub fn mut_last<'a>(&'a mut self) -> Option<&'a mut T> {
         match *self {
             Vec(ref mut v) => v.mut_last(),
-            Empty => fail!("mut_last on empty opt_vec")
+            Empty => None
         }
     }