如何在ruby中发出一次警告？

class SoylentGreen
  def eat
    warn "Algae harvesting not implemented. Soylent green is people!"
  end
end

5.times do
  soylent_green = SoylentGreen.new
  soylent_green.eat
end

产生

Algae harvesting not implemented. Soylent green is people!
Algae harvesting not implemented. Soylent green is people!
Algae harvesting not implemented. Soylent green is people!
Algae harvesting not implemented. Soylent green is people!
Algae harvesting not implemented. Soylent green is people!

理想情况下,我希望它只发生一次.

我没有使用rails,并且可以访问ruby 1.8和1.9.

替代方案包括编写我自己的警告系统(它只会覆盖这样的故意警告),或者将警告放在SoylentGreen #edout之外(即使没有调用该方法也会显示它).

class SoylentGreen
  def eat
    warn_once "Algae harvesting not implemented. Soylent green is people!"
  end
  def warn_once(msg)
    @@warned||=false
    if not @@warned then
       @@warned = true
       warn msg
    end
  end
end