1. 先看如下函数：
class Person
{
public:
Person(const sting& name, const Date& birthday,
const Address& addr, const Country& country);
virtual ~Person();
string name() const;
stirng birthDate() const;
stirng address() const;
string nationality() const;
private:
string name_; //实现细节
Date birthday_; //实现细节
Address address_; //实现细节
Country citizenship_; // 实现细节
}；class Person
{
public:
