PHP new self 、new static 比較

class A {
    public static function get_self() {
        return new self();
    }

    public static function get_static() {
        return new static();
    }
}

class B extends A {
    public function testB(){
        return 'testB';
    }
}

echo get_class(A::get_self()); // A
echo get_class(A::get_static()); // A
echo get_class(B::get_self());  // A
echo get_class(B::get_static()); // B

#echo B::get_self()->testB();  // Fatal error:  Uncaught Error: Call to undefined method A::testB()
echo B::get_static()->testB(); // testB

new self() => 生成的物件為實際寫有這句 code 的 class
new static() =>生成的物件為呼叫使用這句 code 的 class


參考：
php - New self vs. new static - Stack Overflow
class - What does new self(); mean in PHP? - Stack Overflow