Overwrite the handler using Set.

src/list.h

Index: src/list.h
diff --git a/src/list.h b/src/list.h
index 43d982f687a7b37bfe55a128f47e9e8ee8c12eea..0e4e35bb41b78b3ff5aa8b106ea284d1e4ded91c 100644
--- a/src/list.h
+++ b/src/list.h
@@ -115,6 +115,9 @@ class List {
   void InsertAt(int index, const T& element,
                 AllocationPolicy allocator = AllocationPolicy());
 
+  // Overwrites the element at the specific index.
+  void Set(int index, const T& element);
+
   // Added 'count' elements with the value 'value' and returns a
   // vector that allows access to the elements.  The vector is valid
   // until the next change is made to this list.