4 files changed, 20 insertions, 1 deletions
diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 4d2533e782..9217ed99d2 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Added Hash#diff to show the difference between two hashes [Chris McGrath]
+
 * Fixed HashWithIndifferentAccess#delete to work with both symbols and strings #2176 [Caio Chassot]
 
 * Added Time#advance to do precise time time calculations for cases where a month being approximated to 30 days won't do #1860 [Rick Olson]
diff --git a/activesupport/lib/active_support/core_ext/hash.rb b/activesupport/lib/active_support/core_ext/hash.rb
index b8309baea3..7d94d70910 100644
--- a/activesupport/lib/active_support/core_ext/hash.rb
+++ b/activesupport/lib/active_support/core_ext/hash.rb
@@ -2,10 +2,12 @@ require File.dirname(__FILE__) + '/hash/keys'
 require File.dirname(__FILE__) + '/hash/indifferent_access'
 require File.dirname(__FILE__) + '/hash/reverse_merge'
 require File.dirname(__FILE__) + '/hash/conversions'
+require File.dirname(__FILE__) + '/hash/diff'
 
 class Hash #:nodoc:
   include ActiveSupport::CoreExtensions::Hash::Keys
   include ActiveSupport::CoreExtensions::Hash::IndifferentAccess
   include ActiveSupport::CoreExtensions::Hash::ReverseMerge
   include ActiveSupport::CoreExtensions::Hash::Conversions
+  include ActiveSupport::CoreExtensions::Hash::Diff
 end
diff --git a/activesupport/lib/active_support/core_ext/hash/diff.rb b/activesupport/lib/active_support/core_ext/hash/diff.rb
new file mode 100644
index 0000000000..deace40a29
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/hash/diff.rb
@@ -0,0 +1,11 @@
+module ActiveSupport #:nodoc:
+  module CoreExtensions #:nodoc:
+    module Hash #:nodoc:
+      module Diff
+        def diff(h2)
+          self.dup.delete_if { |k, v| h2[k] == v }.merge(h2.dup.delete_if { |k, v| self.has_key?(k) })
+        end
+      end
+    end
+  end
+end
diff --git a/activesupport/test/core_ext/hash_ext_test.rb b/activesupport/test/core_ext/hash_ext_test.rb
index a11cef6fc4..3fc3b86254 100644
--- a/activesupport/test/core_ext/hash_ext_test.rb
+++ b/activesupport/test/core_ext/hash_ext_test.rb
@@ -174,6 +174,10 @@ class HashExtTest < Test::Unit::TestCase
   def test_reverse_merge
     assert_equal({ :a => 1, :b => 2, :c => 10 }, { :a => 1, :b => 2 }.reverse_merge({:a => "x", :b => "y", :c => 10}) )
   end
+
+  def test_diff
+    assert_equal({ :a => 2 }, { :a => 2, :b => 5 }.diff({ :a => 1, :b => 5 }))
+  end
 end
 
 class HashToXmlTest < Test::Unit::TestCase
@@ -234,4 +238,4 @@ class HashToXmlTest < Test::Unit::TestCase
     xml = { :name => "David", :addresses => [{ :streets => [ { :name => "Paulina" }, { :name => "Paulina" } ] } ] }.to_xml(@xml_options)
     assert xml.include?(%(<addresses><address><streets><street><name>))
   end
-end
-\ No newline at end of file
+end