It's interesting to note that the question was "how to design a class", which to me sounds like a question about static structure, e.g. what data members and me

It's interesting to note that the question was "how to design a class", which to me sounds like a question about static structure, e.g. what data members and methods will the class have. Most of the discussion on this and the SO page mixes in OOD, OOP with the original question and then throws in some inappropriate OO vs. FP tangents. It's important to remember that there's a lot of, for lack of a better word, "class-oriented design" which typically tries to model the static structure of the physical world or some artefacts of the programming environment. In a completely separate world there's what I would call OO design and programming which is more concerned about the interaction of actual objects aka. instances of classes. Coming from the statically typed world the distinction is often unclear but for the original Smalltalkers and other OO purists object orientation was never about classes.