+

# File activesupport/lib/active_support/duration.rb, line 41
      def +(other)
        if Duration === other
          seconds   = value + other._parts.fetch(:seconds, 0)
          new_parts = other._parts.merge(seconds: seconds)
          new_value = value + other.value

          Duration.new(new_value, new_parts, other.variable?)
        else
          calculate(:+, other)
        end
      end