1 files changed, 25 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/hash/reverse_merge.rb b/activesupport/lib/active_support/core_ext/hash/reverse_merge.rb
new file mode 100644
index 0000000000..46c53871d8
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/hash/reverse_merge.rb
@@ -0,0 +1,25 @@
+module ActiveSupport #:nodoc:
+  module CoreExtensions #:nodoc:
+    module Hash #:nodoc:
+      # Allows for reverse merging where its the keys in the calling hash that wins over those in the <tt>other_hash</tt>.
+      # This is particularly useful for initializing an incoming option hash with default values:
+      #
+      #   def setup(options = {})
+      #     options.reverse_merge! :size => 25, :velocity => 10
+      #   end
+      #
+      # The default :size and :velocity is only set if the +options+ passed in doesn't already have those keys set.
+      module ReverseMerge
+        def reverse_merge(other_hash)
+          other_hash.merge(self)
+        end
+
+        def reverse_merge!(other_hash)
+          replace(reverse_merge(other_hash))
+        end
+
+        alias_method :reverse_update, :reverse_merge
+      end
+    end
+  end
+end
+\ No newline at end of file