def exclude(*list, &block)
      @@exclusion << list.map { |s| "@#{s}".to_sym }
      @@exclusion.flatten!
      @@exclusion_block = block if block_given?
    end
def exclude(*list, &block)
      @@exclusion << list.map { |s| "@#{s}".to_sym }
      @@exclusion.flatten!
      @@exclusion_block = block if block_given?
    end
exclusion list of instance variables to NOT dup/clone