C++ 打印死亡钻石

Question

首先让我解释一下我的层次结构：

        Person
       /     \
   Student Employee
       \     /
       Intern

每个 class 都有自己的 output 函数，打印它们的数据成员，而我只需要打印一次 Person 。问题是Student和Employee不是抽象的classes，人家也会自己造一个对象，所以我不能只调用[=上的输出函数19=]级.

正如您将在下面的代码中看到的那样，我已经设法解决了这个问题，但我认为这很丑陋而且不是很多态。我创建了一个额外的输出函数，因此它适用于所有情况。有没有更好的方法来实现这一目标？

class Person {
    string name;
    int id;
public:
        virtual void output(ostream& out) {
        out << name << "," << id;
    }
}

学生：

class Student : virtual public Person {
    string major;
    int year;
public:
    virtual void output(ostream& out) {
        Person::output(out);
        out << "," << major << "," << year;
    }
    virtual void outputStudOnly(ostream& out) {
        out << "," << major << "," << year;
    }
};

员工：

class Employee : virtual public Person{
    string jobTitle;
public:
    virtual void output(ostream& out) {
        Person::output(out);
        out << "," << jobTitle;
    }
    virtual void outputEmpOnly(ostream& out) {
        out << "," << jobTitle;
    }
};

实习生：

class Intern : public Student, public Employee {
public:
    virtual void output(ostream& out) {
        Person::output(out);
        Student::outputStudOnly(out);
        Employee::outputEmpOnly(out);
    }
};

Answer 1

模板方法的用途。以下是我将如何编写此代码：

class Person {
    string name;
    int id;
public:
        void output(ostream& out) {
        out << name << "," << id;
        output_impl(out);
    }
private:
       virtual void output_impl(ostream& ) {}
};

class Student : virtual public Person {
    string major;
    int year;
private:
    virtual void output_impl(ostream& out) {
        out << "," << major << "," << year;
    }

};

class Employee : virtual public Person {
    string jobTitle;
private:
    virtual void output_impl(ostream& out) {
        out << "," << jobTitle;
    }
};

class Intern : public Student, public Employee {
private:
    virtual void output_impl(ostream& out) {
        Student::output_impl(out);
        Employee::output_impl(out);
    }
};

然后你在对象上调用 output。

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