1 files changed, 11 insertions, 5 deletions
diff --git a/activesupport/lib/active_support/core_ext/enumerable.rb b/activesupport/lib/active_support/core_ext/enumerable.rb
index eae964bc2e..8ebe758078 100644
--- a/activesupport/lib/active_support/core_ext/enumerable.rb
+++ b/activesupport/lib/active_support/core_ext/enumerable.rb
@@ -34,7 +34,9 @@ module Enumerable
   #     => { "Chade- Fowlersburg-e" => <Person ...>, "David Heinemeier Hansson" => <Person ...>, ...}
   def index_by
     if block_given?
-      Hash[map { |elem| [yield(elem), elem] }]
+      result = {}
+      each { |elem| result[yield(elem)] = elem }
+      result
     else
       to_enum(:index_by) { size if respond_to?(:size) }
     end
@@ -114,11 +116,15 @@ end
 # just calling the compat method in the first place.
 if Array.instance_methods(false).include?(:sum) && !(%w[a].sum rescue false)
   class Array
-    remove_method :sum
+    alias :orig_sum :sum
 
-    def sum(*args) #:nodoc:
-      # Use Enumerable#sum instead.
-      super
+    def sum(init = nil, &block) #:nodoc:
+      if init.is_a?(Numeric) || first.is_a?(Numeric)
+        init ||= 0
+        orig_sum(init, &block)
+      else
+        super
+      end
     end
   end
 end