矩形可按面积比较

Comparable 是 Ruby 中最受欢迎的模块之一。其目的是提供方便的比较方法。

要使用它，你必须 include Comparable 并定义太空船运算符（<=>）：

class Rectangle
  include Comparable

  def initialize(a, b)
    @a = a
    @b = b
  end

  def area
    @a * @b
  end

  def <=>(other)
    area <=> other.area
  end
end

r1 = Rectangle.new(1, 1)
r2 = Rectangle.new(2, 2)
r3 = Rectangle.new(3, 3)

r2 >= r1 # => true
r2.between? r1, r3 # => true
r3.between? r1, r2 # => false