Have a parent class's method access the subclass's constants

Question

For example:

class Animal

 def make_noise
    print NOISE
 end

end

class Dog < Animal
    NOISE = \"bark\"
end

d = Dog.new
d.make_noise # I want this to p         


        

Answer 1

If you're doing this to configure your sub classes so that the base class has access to the constants then you can create a DSL for them like this:

module KlassConfig
  def attr_config(attribute)
    define_singleton_method(attribute) do |*args|
      method_name = "config_#{attribute}"
      define_singleton_method method_name do
        args.first
      end
      define_method method_name do
        args.first
      end
    end
  end
end

class Animal
  extend KlassConfig
  attr_config :noise

  def make_noise
    puts config_noise
  end
end

class Dog < Animal
  noise 'bark'
end

This way is a bit more performant as on each method call you don't have to introspect the class to reach back (or is it forward?) for the constant.