Clock

clock.rb

class Clock
  def self.at(hour, min = 0)
    ClockTime.new(hour, min)
  end
end

class ClockTime
  attr_accessor :time
  
  def initialize(hour, min)
    @time = Time.new(2016,1,1, hour, min)
  end
  
  def to_s
    time.strftime('%H:%M')
  end
  
  def +(min)
    self.time += (min * 60)
    self
  end
  
  def -(min)
    self.time -= (min * 60)
    self
  end
  
  def ==(other)
    to_s == other.to_s
  end
end