CPP friend


### Efficient for [CPP operator overloading](https://texonom.com/cpp-operator-overloading-ea59a048370340668bc23f94017b9f26) 
do not have to access data through accessor and mutator functions
best to make nonmember operator overloads friends
when have to access multi class private variable, otherwise member overloading is better


### Friend Class
Entire classes can be friends
```typeclass Friend1 {private :    string name;     friend class Friend2;};```



### Reference
> [friend 키워드 [friend 전역 함수 , friend 클래스 , friend 멤버 함수]](https://genesis8.tistory.com/98)

> [C++ friend 클래스와 함수](https://yeolco.tistory.com/116)





