Question

I am encountering a strange bug in my code. I have a rails application with the following two files in the lib:

lib/module_one/module_two/class_one.rb

module ModuleOne
  module Moduletwo
    class ClassOne
      class << self
        def test
          puts 'Class one'
          ClassTwo.test
        end
      end
    end
  end
end

and

lib/module_one/module_two/class_two.rb

module ModuleOne
  module ModuleTwo
    class ClassTwo
      def self.test
        puts 'Class two'
      end
    end
  end
end

Now my problem is, that when I go into the console and write:

ModuleOne::ModuleTwo::ClassOne.test

it throws the following: NameError: uninitialized constant ClassTwo

The strange thing is, that the problem seems to be connected to the use of class << self instead of self.method. If I change the class_one.rb file like this it works!:

module ModuleOne
  module ModuleTwo
    class ClassOne
      def self.test
        puts 'Class one'
        ClassTwo.test
      end
    end
  end
end

Im loading the files in application.rb like this:

config.autoload_paths += %W(#{config.root}/lib)

Is this a bug in rails, or is it just me getting something all wrong?

Im using rails 3.1.3 btw

Answer 1

(Only a partial answer, but need formatting.)

It’s because of how class << self works.

For example, if you change it to:

class << self
  def test
    self::ClassTwo.test
  end
end

it works fine.

---

Edit; too long for reasonable comment.

I’m poking around a bit… On an intuitive level it makes sense to me, I’m just not sure why yet. Don’t know if I knew a real reason once, or if I’m just making it up.

I’m not sure why self seems to refer to the module, though; the “Programming Ruby 1.9” book doesn’t go in to enough depth on the class << semantics. I’ll tweet something and refer to this question and someone smarter will create a real answer.