一个类继承一个单例还是单例的实现

class A
{
   static $inc;
   private function __construct(){}
   private function __clone(){}
   public static function get_self()
   {
      if(!(self::$inc instanceof self)){
         self::$inc =  new self();
      }
      return self::$inc;
   }
   
   public static function get_static()
   {
      if(!(self::$inc instanceof self)){
         self::$inc =  new static();//主要就是实例static
      }
      return self::$inc;
   }
   
   public function geta(){
      echo 111;
   }
}

class B extends A
{
   static $inc;
   private function __construct(){}
   private function __clone(){}
   public function gethh(){
      echo 222;
   }
}



$obj = B::get_static();
//var_dump($obj);
//echo "<br />";
$obj->geta();
$obj->gethh();