From d9fadbc04f5bbd520e4ce8665ac128288e9846c0 Mon Sep 17 00:00:00 2001
From: Nathaniel Herman <nherman@college.harvard.edu>
Date: Sun, 26 Jan 2014 11:24:34 -0500
Subject: Make mut_last return Option instead of failing on empty vector (and
 add a test for mut_last)

---
 src/libstd/vec.rs | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

(limited to 'src/libstd')

diff --git a/src/libstd/vec.rs b/src/libstd/vec.rs
index 81e3e6c7eda..0b9820e12eb 100644
--- a/src/libstd/vec.rs
+++ b/src/libstd/vec.rs
@@ -2031,7 +2031,7 @@ pub trait MutableVector<'a, T> {
     fn mut_iter(self) -> MutItems<'a, T>;
 
     /// Returns a mutable pointer to the last item in the vector.
-    fn mut_last(self) -> &'a mut T;
+    fn mut_last(self) -> Option<&'a mut T>;
 
     /// Returns a reversed iterator that allows modifying each value
     fn mut_rev_iter(self) -> RevMutItems<'a, T>;
@@ -2298,10 +2298,10 @@ impl<'a,T> MutableVector<'a, T> for &'a mut [T] {
     }
 
     #[inline]
-    fn mut_last(self) -> &'a mut T {
+    fn mut_last(self) -> Option<&'a mut T> {
         let len = self.len();
-        if len == 0 { fail!("mut_last: empty vector") }
-        &mut self[len - 1]
+        if len == 0 { return None; }
+        Some(&mut self[len - 1])
     }
 
     #[inline]
@@ -4305,6 +4305,16 @@ mod tests {
         let mut y: &mut [int] = [];
         assert!(y.mut_pop_ref().is_none());
     }
+
+    #[test]
+    fn test_mut_last() {
+        let mut x = [1, 2, 3, 4, 5];
+        let h = x.mut_last();
+        assert_eq!(*h.unwrap(), 5);
+
+        let mut y: &mut [int] = [];
+        assert!(y.mut_last().is_none());
+    }
 }
 
 #[cfg(test)]
-- 
cgit 1.4.1-3-g733a5