Merge branch 'master' of github.com:lifo/docrails

1 files changed, 8 insertions, 2 deletions

diff --git a/activesupport/lib/active_support/core_ext/enumerable.rb b/activesupport/lib/active_support/core_ext/enumerable.rb
index b950826396..03efe6a19a 100644
--- a/activesupport/lib/active_support/core_ext/enumerable.rb
+++ b/activesupport/lib/active_support/core_ext/enumerable.rb
@@ -17,6 +17,7 @@ module Enumerable
   # The default sum of an empty list is zero. You can override this default:
   #
   #  [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)
+  #
   def sum(identity = 0, &block)
     if block_given?
       map(&block).sum(identity)
@@ -31,6 +32,7 @@ module Enumerable
   #     => { "nextangle" => <Person ...>, "chade-" => <Person ...>, ...}
   #   people.index_by { |person| "#{person.first_name} #{person.last_name}" }
   #     => { "Chade- Fowlersburg-e" => <Person ...>, "David Heinemeier Hansson" => <Person ...>, ...}
+  #
   def index_by
     if block_given?
       Hash[map { |elem| [yield(elem), elem] }]
@@ -63,11 +65,15 @@ class Range #:nodoc:
   # Optimize range sum to use arithmetic progression if a block is not given and
   # we have a range of numeric values.
   def sum(identity = 0)
-    if block_given? || !(first.instance_of?(Integer) && last.instance_of?(Integer))
+    if block_given? || !(first.is_a?(Integer) && last.is_a?(Integer))
       super
     else
       actual_last = exclude_end? ? (last - 1) : last
-      (actual_last - first + 1) * (actual_last + first) / 2
+      if actual_last >= first
+        (actual_last - first + 1) * (actual_last + first) / 2
+      else
+        identity
+      end
     end
   end
 end