Added Hash#deep_dup function which performs deep duplication on given hash

activesupport/lib/active_support/core_ext/hash.rb

@@ -1,5 +1,6 @@
 require 'active_support/core_ext/hash/conversions'
 require 'active_support/core_ext/hash/deep_merge'
+require 'active_support/core_ext/hash/deep_dup'
 require 'active_support/core_ext/hash/diff'
 require 'active_support/core_ext/hash/except'
 require 'active_support/core_ext/hash/indifferent_access'

activesupport/lib/active_support/core_ext/hash/deep_dup.rb

@@ -0,0 +1,11 @@
+class Hash
+  # Returns a deep copy of hash.
+  def deep_dup
+    duplicate = self.dup
+    duplicate.each_pair do |k,v|
+      tv = duplicate[k]
+      duplicate[k] = tv.is_a?(Hash) && v.is_a?(Hash) ? tv.deep_dup : v
+    end
+    duplicate
+  end
+end

activesupport/test/core_ext/hash_ext_test.rb

@@ -316,6 +316,21 @@ def test_deep_merge_on_indifferent_access
     assert_equal expected, hash_1
   end
 
+  def test_deep_dup
+    hash = { :a => { :b => 'b' } }
+    dup = hash.deep_dup
+    dup[:a][:c] = 'c'
+    assert_equal nil, hash[:a][:c]
+    assert_equal 'c', dup[:a][:c]
+  end
+
+  def test_deep_dup_initialize
+    zero_hash = Hash.new 0
+    hash = { :a => zero_hash }
+    dup = hash.deep_dup
+    assert_equal 0, dup[:a][44]
+  end
+
   def test_store_on_indifferent_access
     hash = HashWithIndifferentAccess.new
     hash.store(:test1, 1)