# File lib/active_record/attribute_methods.rb, line 84
      def instance_method_already_implemented?(method_name)
        return true if method_name =~ /^id(=$|\?$|$)/
        @_defined_class_methods         ||= Set.new(ancestors.first(ancestors.index(ActiveRecord::Base)).collect! { |m| m.public_instance_methods(false) | m.private_instance_methods(false) | m.protected_instance_methods(false) }.flatten)
        @@_defined_activerecord_methods ||= Set.new(ActiveRecord::Base.public_instance_methods(false) | ActiveRecord::Base.private_instance_methods(false) | ActiveRecord::Base.protected_instance_methods(false))
        raise DangerousAttributeError, "#{method_name} is defined by ActiveRecord" if @@_defined_activerecord_methods.include?(method_name)
        @_defined_class_methods.include?(method_name)
      end