Effective C++ Item 23 Prefer non-member non-friend functions to member functions

Question

While puzzling with some facts on class design, specifically whether the functions should be members or not, I looked into Effective c++ and found Item 23, namely, Prefer no

Answer 1

The criteria I use is if a function could be implemented significantly more efficiently by being a member function, then it should be a member function. ::std::sort does not meet that definition. In fact, there is no efficiency difference whatsoever in implementing it externally vs. internally.

A vast efficiency improvement by implementing something as a member (or friend) function means that it greatly benefits from knowing the internal state of the class.

Part of the art of interface design is the art of finding the most minimal set of member functions such that all operations you might want to perform on the object can be implemented reasonably efficiently in terms of them. And this set should not support operations that shouldn't be performed on the class. So you can't just implement a bunch of getter and setter functions and call it good.