Question

What is your rule for which functions that operate on a class should be member functions vs. nonmember functions? For example, I have a class which represents a maze using a matrix of bools. I am making a function called isConnected which verifies that 2 points in the maze are in the same region (i.e. it is possible to travel from A to B).

Should this be member or nonmember? What is a good rule?

Answer 1

When to make it a member function:

• when the function is logically coupled with the class (like your maze connectedness example)
• when the function needs to access private or protected members, it’s better to make it a member than a friend.

When to make it a standalone function

• when it’s a generic function that can be templatized to naturally work on other classes (look at the <algorithms> header for good example)