今天看到《Building a Binary Tree with Enumerable》，正好我与作者的看法相同，module和block是Ruby的特点。
class Node
include Enumerable
attr_accessor :data, :left, :right
def initialize(data)
@data = data
end
def each(&block)
left.each(&block) if left
block.call(self)
right.each(&block) if right
end
def <=>(other_node)
data <=> other_node.data
end
end
root = Node.new(3)
root.left = Node.new(2)
root.right = Node.new(1)
root.each {|x| puts x.data }
# just a few of the various operations Enumerable provides
puts "SUM"
puts root.inject(0) { |memo, val| memo += val.data }
puts "MAX"
puts root.max.data
puts "SORT"
puts root.sort.map(&:data)