require 'drb/drb' 

class Warner          ### An abstract observer of Ticker objects.
def initialize(ticker, limit)
    @limit = limit
    ticker.add_observer(self)
  end
end

class WarnLow < Warner
  def update(time, price)       # callback for observer
    if price < @limit
      print "--- #{time.to_s}: Price below #@limit: #{price}\n"
    end
  end
end

class WarnHigh < Warner
  def update(time, price)       # callback for observer
    if price > @limit
      print "+++ #{time.to_s}: Price above #@limit: #{price}\n"
    end
  end
end

ticker = DRbObject.new_with_uri('druby://localhost:9191')
low = WarnLow.new(ticker, 80)
WarnHigh.new(ticker, 120)