Question

as the title says,

what is the difference between @var and @@var in a class definition?
Also, what is the difference between self.mymethod and mymethod in defining a method?

Answer 1

self always refers to the current object.Check the following Eg:-

class Test 
  def test  
    puts "At the instance level, self is #{self}"  
  end  
  def self.test  
    puts "At the class level, self is #{self}"  
  end  
end  
Test.test   
 #=> At the class level, self is Test  
Test.new.test   
 #=> At the instance level, self is #<Test:0x28190>  

object variables are so named because they have scope within, and are associated
to, the current object.an object variable, is then accessible from any other method inside that object.

Class variables are particularly useful for storing information relevant to all objects
of a certain class.