hoge.txt

[39] pry(main)> module Hoge
[39] pry(main)*   module ClassMethods
[39] pry(main)*     def hoge
[39] pry(main)*       @@hoge = 1
[39] pry(main)*     end     
[39] pry(main)*   end     
[39] pry(main)*   def self.included(cls)   
[39] pry(main)*     cls.extend ClassMethods    
[39] pry(main)*   end     
[39] pry(main)* end     
=> nil
[40] pry(main)> class Ni
[40] pry(main)*   include Hoge
[40] pry(main)*   hoge
[40] pry(main)* end  
=> 1
[41] pry(main)> class Ni
[41] pry(main)*   @@hoge
[41] pry(main)* end  
NameError: uninitialized class variable @@hoge in Ni
from (pry):167:in `<class:Ni>'
[42] pry(main)> class << Ni
[42] pry(main)*   @@hoge
[42] pry(main)* end  
(pry):170: warning: class variable access from toplevel
NameError: uninitialized class variable @@hoge in Object