假定 a2 是 A 的实例，这将调用复制构造函数.

Assuming a2 is an instance of A, this calls the copy constructor.

它将调用 operator new 来获取对象的动态内存，然后它将新对象复制-构造到内存中，然后返回指向该内存的指针.

It will call operator new to get dynamic memory for the object, then it will copy-construct a new object into the memory, then return a pointer to that memory.