如果你需要运行时多态，你不能使用按值传递。

If you need runtime polymorphism, you must not use pass-by-value.

youdao

通常按值传递参数，除非希望过程能够更改其在调用代码中的值。

Normally you pass a parameter by value, unless you want the procedure to be able to change its value in the calling code.

youdao

重要事项对于引用类型，按值传递参数会得到对所传递对象的引用的副本。

For reference types, if you pass a parameter by value, it results in a copy of the reference to an object being passed.

youdao