<?phpclass A{protectedstatic$instance =null;publicstaticfunctiongetInstance(...$args)    {if(!isset(self::$instance)){self::$instance =newstatic(...$args);        }returnself::$instance;    }publicfunctiongetB()    {return B::class::getInstance();    }}class Bextends A{protectedstatic$instance =null;publicstaticfunctiongetInstance(...$args)    {if(!isset(self::$instance)){self::$instance =newstatic(...$args);        }returnself::$instance;    }}var_dump(A::getInstance()->getB());// B

<?phptrait Singleton{    protected static $instance = null;    public static function getInstance(...$args)    {        if(!isset(self::$instance)){            self::$instance = new static(...$args);        }        return self::$instance;    }}class A{    use Singleton;    public function getB()    {        return B::class::getInstance();    }}class B extends A{    use Singleton;}var_dump(A::getInstance()->getB()); // A

var_dump(A::getInstance()->getB()); // B