Practise 2 from Well Grounded Rubyist

practise_2.rb

class Car
  #CLASS LEVEL VARIABLES AND METHODS
  @@makes = []
  @@cars = {}


  def self.total_count     #ATTRIBUTE READER
    @total_count ||= 0
  end

  def self.total_count=(n)  #ATTRIBUTE WRITER
    @total_count = n
  end

  def self.show_makes    # ATTRIBUTE READER FOR MAKES
    return @@makes
  end

  def self.add_make(make) #ADD MAKE TO @@MAKES
    unless @@makes.include?(make) #CHECK MAKE DOES NOT EXIST
      @@makes << make #APPENDS ARGUMENT make TO @@MAKES
      @@cars[make] = 0 # INITIALISES KEY make => value 0 to @@CARS
      puts "Added make #{make}" #CONFIRMS MAKE ADDED
    end
  end

#INSTANCE OBJECT LEVEL VARIABLE AND METHODS
  attr_reader :make

  def initialize(make)
    if @@makes.include?(make)
      puts "Creating new make #{make}!"
      @make = make
      @@cars[make] +=1
      self.class.total_count +=1 #writes TO LINE 11
    else
      puts "No such make #{make}."
    end
  end

  def make_mates
    @@cars[self.make]
  end
end


c = Car.new("First make")
puts Car.total_count
Car.add_make("Nissan")
Car.add_make("VOLVO")
d = Car.new("Nissan")
#e = Car.new("Volvo")
puts Car.total_count
puts d.make
puts Car.show_makes