Demonstrating the spaceship operator.

cuttlefish.rb

class Cuttlefish
  # Because we've defined <=> we can use all the Comparable methods
  # http://ruby-doc.org/core-2.0/Comparable.html
  include Comparable
  attr_reader :name, :ink_capacity

  def initialize(name, ink_capacity = 0)
    @name = name
    @ink_capacity = ink_capacity
  end

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

c1 = Cuttlefish.new('Albert')
c2 = Cuttlefish.new('Bertie', 200)
c3 = Cuttlefish.new('Cyril', 150)

puts c1 > c2 # 0 > 200 => false
puts c3 > c2 # 150 > 200 => false
puts c3.between?(c1, c2) # 150 between 0 and 200 => true
puts [c1, c2, c3].sort.inspect # Sorted in ascending order by :ink_capacity