Attributes can be dup-ed

activemodel/lib/active_model/attributes.rb

@@ -77,6 +77,11 @@ module ActiveModel
       super
     end
 
+    def initialize_dup(other) # :nodoc:
+      @attributes = @attributes.deep_dup
+      super
+    end
+
     # Returns a hash of all the attributes with their names as keys and the values of the attributes as values.
     #
     #   class Person

activemodel/test/cases/attributes_test.rb

@@ -108,6 +108,21 @@ module ActiveModel
       assert_equal attributes, new_attributes
     end
 
+    test "attributes can be dup-ed" do
+      data = ModelForAttributesTest.new
+      data.integer_field = 1
+
+      duped = data.dup
+
+      assert_equal 1, data.integer_field
+      assert_equal 1, duped.integer_field
+
+      duped.integer_field = 2
+
+      assert_equal 1, data.integer_field
+      assert_equal 2, duped.integer_field
+    end
+
     test "can't modify attributes if frozen" do
       data = ModelForAttributesTest.new
       data.freeze