def each_key(start = nil)
      cursor_in_loop(start) do |iterator|
        throw(:finish_iteration) unless key = iterator.key
        yield cast_key_out(key)
      end
    end
def each_key(start = nil)
      cursor_in_loop(start) do |iterator|
        throw(:finish_iteration) unless key = iterator.key
        yield cast_key_out(key)
      end
    end
Iteration