Ruby和类变量继承类

class A
  def set(v)
    @@v = v
  end
  def put
    puts @@v
  end
end

class B < A
end
class C < A
end

B.new.set 'b'
B.new.put # => b
C.new.set 'c'
C.new.put # => c
B.new.put # => c
class A
  def set(v)
    @@v = v
  end
  def pu