stdClass

class standardClass extends stdClass
{

    public function __get( $index )
    {

        if( !isset( $this->$index ) || !$this->$index instanceof stdClass )
        {
            $this->$index = new standardClass();
            return $this->$index;
        }
        else
        {
            return $this->$index;
        }

    }

}

$x = new standardClass();
$x->y->z = 123;
print_r( $x );