ruby - Derived Class shares class variables? -

i have class cache , 2 derived classes foo , bar (simplification, principle same).

class cache    @@test = []    def self.test     @@test   end   def self.add(value)    @@test << value  end  end  class foo < cache end  class bar < cache end 

running following leads me conclude @@test not unique foo , bar, unique cache, don't want nor expect.

foo.add(1) #[1] bar.add(2) #[1,2] puts foo.test #[1,2] 

isn't supposed be:

foo.add(1) #[1] bar.add(2) #[2] puts foo.test #[1] 

how can behaviour want? why ruby doing strange?

the solution in case not use static classes, 2 instances of class wanted , storing them in static variable.