知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。 @MarkusMeskanen: because the object is immutable, and if you mutated it in position you can not specialise it in the subclass. This was spotted by Khushal Bherwani who posted an illustration on X, I am in a position to duplicate it, here is my GIF of it https://gurgaonproject.business.blog/