module Serializer
  def serialize
    puts "Serializing to string"
  end
end

class BaseSerializer
  include Serializer
end

class JsonSerializer < BaseSerializer
  def serialize
    puts "Serializing to JSON"
  end
end

class StringSerializer < BaseSerializer
end

JsonSerializer.new.serialize # Calls JsonSerializer::serialize#
StringSerializer.new.serialize # Calls Serializer::serialize#