Is it possible to replace:
是否可以将视频里向量扩容代码中的：
for (int i = 0; i < _size; i++) _elem[i] = oldElem[i];
in the vector expansion code in the video with:
替代为：
memcpy(_elem, oldElem, _size * sizeof(T));
答案：
No, because whether the latter can achieve the purpose is related to element type T.
否，因为后者能否达到目的与元素类型T有关。
分析：
When T is a non-base type and there is a corresponding assignment operator to perform deep copy, the previous section of code calls the assignment operator, and the latter section can only perform shallow copy.
当T为非基本类型且有对应的赋值运算符以执行深复制时，前一段代码会调用赋值运算符，而后一段只能进行浅复制。
