Ruby: NoMethodError: undefined method when Mutating Instance Variable

Question

I am writing a program that will reshuffle passengers on the bus. I want to record how many shuffles it takes to re-order the seating on the bus. Thought I had it, but I cannot change self.reshuffle_count. How do I access @reshufffle_count from the method reshuffle_seating

class MagicBus < Array

  attr_writer :seating

  def seating
    @seating || []
  end

  def reshuffle_count
    @reshuffle_count || 0
  end

def reshuffle_seating
    max_passengers = self.seating.max
    popular_seat = self.seating.max
    pop_seat_indx = self.seating.find_index(popular_seat)
    reshuffle_num = 0
    self.seating.rotate!(pop_seat_indx)
    while popular_seat > 1 do 
      self.seating.each_with_index do |seat, index|
      if index != 0
        self.seating[index] = self.seating[index] +1
        popular_seat = popular_seat -1
      else
        reshuffle_num = reshuffle_num +1
        p reshuffle_num
      end
      end
    end
    self.seating.rotate!(pop_seat_indx*-1)
    self.seating[pop_seat_indx] = popular_seat
    self.reshuffle_count = reshuffle_num   
  end
end

class TestMagicBusSeating < MiniTest::Test
def test_reshuffle_seating_instance1
    bus = MagicBus.new
    bus.seating = [0,2,7,0]
    bus.reshuffle_seating
    assert_equal([2, 4, 1, 2], bus.seating)
    assert_equal(5, bus.reshuffle_count)
  end
end

Error Message is

Error:
TestMagicBusSeating#test_reshuffle_seating_instance1:
NoMethodError: undefined method `reshuffle_count=' for []:MagicBus
Did you mean?  reshuffle_count
    magic_bus.rb:99:in `reshuffle_seating'
    magic_bus.rb:217:in `test_reshuffle_seating_instance1'

Answer 1

NoMethodError: undefined method `reshuffle_count='

That means you are missing a setter. You have the getter defined def reshuffle_count but no setter.

class MagicBus < Array

  attr_writer :seating

  def seating
    @seating || []
  end

  def reshuffle_count=(value)
    @reshuffle_count=value
  end

  def reshuffle_count
    @reshuffle_count || 0
  end
  .....

Or as @tadman pointed out, attr_writer :resuffle_count