What are some alternatives to friend functions?

Alternatives to friend functions are: Encapsulating class methods: Define methods in the private part of the class and expose them as friend functions to maintain encapsulation and allow external access to private members. Bridge mode: Use the bridge class to contain a pointer to the target class, and add a friend function to it to delegate the target class method. Template metaprogramming: Use template metaprogramming to manipulate class members at compile time to allow access to private members.

An alternative to friend functions

A friend function is a special type of function that can access private members of other classes. Although friend functions are convenient, they also break encapsulation. Therefore, when designing a class, it is best to avoid using friend functions as much as possible.

The following are some alternatives to friend functions:

Encapsulating class methods:

Define a method in the private part of the class and encapsulate it Exposed as a friend function. This maintains encapsulation while still allowing external functions to access private members.

Use bridge mode:

Create a bridge class that contains a pointer to the destination class. Add the friend function to the bridge class, and then delegate the methods of the target class to the friend function.

Using template metaprogramming:

Use template metaprogramming to manipulate class members at compile time. This method is more complex, but allows access to private members at runtime.

Practical case:

Suppose we have a Person class whose private members are name and age . We need to define a printInfo function to print Person information.

// 使用封装类方法
class Person {
private:
    std::string name;
    int age;

    friend void printInfo(const Person& p) {
        std::cout << "Name: " << p.name << std::endl;
        std::cout << "Age: " << p.age << std::endl;
    }
};

// 使用桥接模式
class PersonBridge {
private:
    Person* person;

public:
    PersonBridge(Person* p) : person(p) {}

    void printInfo() {
        std::cout << "Name: " << person->name << std::endl;
        std::cout << "Age: " << person->age << std::endl;
    }
};

// 使用模板元编程
template <typename T>
void printInfo(const T& p) {
    std::cout << "Name: " << p.name << std::endl;
    std::cout << "Age: " << p.age << std::endl;
}

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