Pattern for class inheritable_attributes that was removed from rails 3.2

class_inheritable_attribute_pattern.rb

class SomeClass
  self.instance_variable_set('@my_attribute', {:class => true})
  def self.my_attribute; @my_attribute; end

  def self.inherited(klass)
    val = self.instance_variable_get('@my_attribute')
    klass.instance_variable_set('@my_attribute', val.duplicable? ? val.dup : val)
    super
  end
end

class AnotherClass < SomeClass; end

SomeClass.my_attribute # => {:class => true}
AnotherClass.my_attribute # => {:class => true}

AnotherClass[:subclass] = true
SomeClass.my_attribute # => {:class => true}
AnotherClass.my_attribute # => {:class => true, :subclass => true}