ruby.rb

class Foo
  @foo_count = 0   <---- instance variable
  
  def self.increment_counter <---- class method
    @foo_count += 1
  end
  
  def self.current_count
    @foo_count
  end  
end

class Bar < Foo
  @foo_count = 100
end

Foo.increment_counter  <---- how class method can access to instance variable?