pen.rb

class Pen
  include Comparable
  attr :serialNumber, :length

  def initialize(serialNumber, length)
    @serialNumber = serialNumber
    @length = length
  end

  def to_s
    "SN: #{serialNumber}, length: #{length}"
  end

  def <=>(other)
    if length > other.length
      1
    elsif length < other.length
      -1
    else
      0
    end
  end

  def ==(other)
    return true if object_id == other.object_id
    return false unless other.is_a?(Pen)
    return serialNumber == other.serialNumber
  end
end


pensInMyPocket = []
pensInMyPocket << Pen.new("a", 10)
pensInMyPocket << Pen.new("a", 4)
pensInMyPocket << Pen.new("b", 15)
pensInMyPocket << Pen.new("c", 7)
pensInMyPocket << Pen.new("b", 1)

puts "Before sort by length:"
pensInMyPocket.each { |pen| puts "\t#{pen}" }

puts "After sort by length:"
pensInMyPocket.sort.each { |pen| puts "\t#{pen}" }