On: Getter-Setter Pattern Considered Harmful

[jmull]

I think you should take a minute to think about it.

Let me turn it around on you: Give me a simple example in code of something that is mutable and not state.

I'll come back later to check your answer and provide one of my own, if necessary.

[jmull → jmull]

OK, here it is:

    int addOne(int value) {
        value += 1;
        return value;
    }

value is clearly mutable, yet not state.

State is a value you can refer to later. Here, "value" doesn't outlive the function, so can't be referred to later.

State is a complication because you have to worry about whether it remains up-to-date.

(Mutable state is even more complex because you also have to worry about if/when it may be changed.)