jruby-6616.rb

require 'set'

class LinkedList
  include Enumerable

  def initialize(head, tail = nil)
    @head, @tail = head, tail
  end

  def <<(item)
    LinkedList.new(item, self)
  end

  def inspect
    [@head, @tail].inspect
  end

  def each(&block)
    block.call(@head)
    @tail.each(&block) if @tail
  end
end

list = LinkedList.new(73) << 12 << 42

puts list

s = Set.new(list)
puts s.size