keyword - When to use friend class in C++

Question

(This question already has answers here): question from:https://stackoverflow.com/questions/521754/when-to-use-friend-class-in-c

Answer 1

I agree with the comments that say the friend keyword can improve encapsulation if used wisely. I'd just add that the most common (legitimate!) use for friend classes may be testing. You may want a tester class to have a greater degree of access than other client classes would have. A tester class could have a good reason to look at internal details that are deliberately hidden from other classes.