If you need runtime polymorphism, you must not use pass-by-value.
如果你需要运行时多态，你不能使用按值传递。
Why does declaring runtime polymorphism for template instantiations result in linker error?
为什么声明为模板实例化运行时多态导致链接器错误呢？
How to calculate the circumference of the three-dimensional graphics (what function)? Required to achieve runtime polymorphism.
对立体图形周长怎么计算(用什么函数)？要求实现运行时的多态性。
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