如何使用包含内部类的类的实例有效地访问内部类的成员？

Question

I want to design a structure using 5 particular classes:Person,Driver,Employee,Child and Parent.

-Every driver is a person.

-Every employee is both a driver and a person.

-Every child is a person.

-Every parent is a person,driver,employee and it can have one or more children.

Here's what I had in mind:

class Parent {
public:
    class Employee {
    public:
        class Driver {
        public:
            class Person {
                string name;
                int age;
            public:
                string GetName() { return name; }
                void SetName(string name) { this->name = name; }
                int GetAge() { return age; }
                void SetAge(int age) { this->age = age; }
            };
        private:
            Person person;
            string carName;
        public:
            Person GetPerson() { return person;}
            void SetPerson(Person person) { this->person = person;}
            string GetCarName() { return carName; }
            void SetCarName(string carName) { this->carName = carName;}
        };
    private:
        Driver driver;
    public:
        Driver GetDriver() { return driver; }
        void SetDriver(Driver driver) { this->driver = driver; }
    };
    class Child {
    public:
        class Person:public Employee::Driver::Person {
        };
    private:
        Person person;
        string nameOfSchool;
    public:
        Person GetPerson() { return person; }
        void SetPerson(Person person) { this->person = person;}
        string GetNameOfSchool(){ return nameOfSchool;}
        void SetNameOfSchool(string nameOfSchool) { this->nameOfSchool = nameOfSchool;}
    };
private:
    Employee employee;
    Child child;
public:
    Employee GetEmployee() { return employee; }
    void SetEmployee(Employee employee) { this->employee = employee;}
    Child GetChild() { return child;}
    void SetChild(Child child) { this->child = child;}
};

But when I try something like:

Parent random_parent;
    random_parent.GetEmployee().GetDriver().GetPerson().SetName("Joseph");
    random_parent.GetEmployee().GetDriver().GetPerson().SetAge(80);
    cout << random_parent.GetEmployee().GetDriver().GetPerson().GetName() << endl << random_parent.GetEmployee().GetDriver().GetPerson().GetAge();

I get just this garbage value:

-858993460

How can I make any instance of Parent work and be able to access and initialize the name and age from inner class Person ?

Answer 1

Design-wise, driver, employee, child and parent are not descendants of a Person. They are rather roles and one Person can have any number of roles. Or, they can be relationships between 2 persons, where, for example, a person is child to one person and a parent to another.

Answer 2

GetPerson , GetDriver , GetChild and GetEmployee should return either references or pointers. Right now, when you call random_parent.GetEmployee() , it returns a brand new, temporary, Employee object which is a copy of the one in random_parent . If you do random_parent.GetEmployee().SetDriver(new_driver) , it sets the driver in this brand new Employee object, not the one in random_parent . The temporary Employee object is then discarded after the statement is executed.

If you change

Employee GetEmployee() { return employee; }

to

//     here
//      |
//      V
Employee& GetEmployee() { return employee; }

then random_parent.GetEmployee() will return a reference to the employee object in random_parent . random_parent.GetEmployee().SetDriver(new_driver); will update that object, which is what you expected to happen.

Do the same with GetDriver , GetPerson , and GetChild .

---

This fixes your immediate problem. However, your code is poorly designed. You could get design advice on Code Review .