Access a Ruby module's method within same module - ruby-on-rails

Question

I'm new to Ruby and probably don't understand something basic:
I'm trying this:
# lib/common_stuff.rb
module CommonStuff
def self.common_thing
# code
#x = second_thing # --> should access method in same module. Doesn't work.
end
def self.second_thing
# code
end
end
# app/controllers/my_controller.rb
require 'common_stuff'
class MyController < ApplicationController
include CommonStuff
y = self.common_thing # accesses the Module method -> works
end
Error:
NoMethodError (undefined method `second_thing' for
MyController:0x000000088d8990): lib/common.rb:7:in 'common_thing'
I tried both with Module and instance methods. Also declaring only the second_thing an instance method or both methods in the Module as instance methods doesn't work. What do I misunderstand?
** EDIT Corrections**
I realized that my mistake was to make the methods class methods (with self. prefix). Without that it actually works. Thought I tried that, but I must have been blind yesterday. So the working code is (just a constructed example - normally I wouldn't instantiate the controller of course):
# lib/common_stuff.rb
module CommonStuff
def common_thing
#x = second_thing # --> access method in same module. Works now too.
end
def second_thing
10
end
end
# app/controllers/my_controller.rb
require 'common_stuff.rb'
class MyController
include CommonStuff
def a_class
y = common_thing # accesses the Module method -> works
puts y
end
end
ctrl = MyController.new
ctrl.a_class

Answer 1

What do I misunderstand?
1) An #variable is private, so you always need to provide an accessor method to access it (or use instance_variable_get() to violate privacy):
module CommonStuff
def common_thing
#x = second_thing # --> should access method in same module. Doesn't work.
end
def second_thing
10
end
end
class MyController
include CommonStuff
attr_accessor :x
end
obj = MyController.new
obj.common_thing
puts obj.x
--output:--
10
2) You can't include a module's class methods:
module CommonStuff
def self.common_thing
puts 'hello'
#x = second_thing # --> should access method in same module. Doesn't work.
end
def self.second_thing
10
end
end
class MyController
include CommonStuff
end
CommonStuff.common_thing
MyController.common_thing
--output:--
hello
1.rb:21:in `<main>': undefined method `common_thing' for MyController:Class (NoMethodError)
#obj = MyController.new
#obj.common_thing #Same error here
If you want to inject some class methods into MyController, you need to rework your CommonStuff module:
module CommonStuff
def self.included(includer) #Advanced 'hook' method
includer.extend ClassMethods
end
module ClassMethods
def common_thing
puts 'hello'
#x = second_thing # --> should access method in same module. Doesn't work.
end
def second_thing
10
end
end
end
class MyController
include CommonStuff
y = common_thing
puts y
puts instance_variable_get(:#x)
end
--output:--
10
10
The hook method is called whenever the module is included by another class/module, and the method is passed the including class/module as an argument.
Response to commment:
Only a controller's instance variables are made available in a view, e.g.:
class MyController
def do_stuff
#x = 10 #instance variable
end
end
but #variables created inside class methods are not the controller's instance variables:
class MyController
def self.do_stuff
#x = 10
end
end
Therefore, #variables created inside class methods will not be available in the view.