Are the instance variables the new global variables?

Question

lately I'm having the feeling that instances variables have the same problems of global variables, I googled about this and found this old article that more or less describes the potential problem i'm seeing.

What good practices do you use to avoid that the same problems of global variables affect instance variables or class variables?

Answer 1

Classes are much smaller than global structure so the impact of an instance variable is much smaller. By keeping small class sizes and adhering closely to the single responsibility principle, much of the downside of a global variable is averted. If the instance variable is created from a passed in parameter then I often make that parameter required in the constructor making the dependency explicit. Also the instance variable is encapsulated well, never being directly modified outside of the instance's methods making it very easy to determine where the instance variable is modified. Finally the instance variable must make sense to the class as a whole or must be private.