Code samples for the "Private constants in Ruby" article

0_simple.rb

class CPUOpponent
  def self.base_points
    1000
  end
  private_class_method :base_points
end

puts CPUOpponent.base_points
# => NoMethodError: private method ‘base_points’ called for CPUOpponent:Class

1_base_points_with_hash.rb

def self.base_points
  @base_points ||= { easy: 1000, medium: 2000, hard: 3000 }
end

2_private_class_method.rb

class CPUOpponent
  def self.base_points
    @base_points ||= { easy: 1000, medium: 2000, hard: 3000 }
  end
  private_class_method :base_points
  
  base_points[:super_hard] = 9001
  puts base_points.inspect
  # => {:medium=>2000, :hard=>3000, :super_hard=>9001, :easy=>1000}
end

3_frozen.rb

class CPUOpponent
  def self.base_points
    @base_points ||= { easy: 1000, medium: 2000, hard: 3000 }.freeze
  end
  private_class_method :base_points

  base_points[:super_hard] = 9001
  puts base_points.inspect
  # => TypeError: can't modify frozen hash
end

4_final.rb

class CPUOpponent
  def self.base_points
    @base_points ||= { easy: 1000, medium: 2000, hard: 3000 }.freeze
  end
  private_class_method :base_points

  def calculate_score(bonus_points)
    base_points = self.class.send(:base_points)
    bonus_points + base_points[:easy]
  end
end

opponent = CPUOpponent.new
puts opponent.calculate_score(400)
# => 1400