Rails constant lookup WTF

constant_lookup.rb

# Rails autoloading constant functionality is useful until it's not.
# Every class is placed in the right file on the right path.

# in app/models/users/serializer.rb
module Users
  class Serializer
    #...
  end
end

# in app/models/users/publish.rb
module Users
  class Publish
    # this works
    def self.user(user)
      publish(Serializer.new(user))
    end
    
    class << self
      # this does not work, Rails cannot lookup Serializer constant
      def user(user)
        publish(Serilaizer.new(user)
      end
      
      # this does work because the full name of the class is specified
      def user(user)
        publish(Users::Serializer.new(user))
      end
    end
    
    def self.publish(ser)
      # ...
    end
  end
end