is there a rule, that would check for unnecessary functions in final classes? For example

isInputValid()

:

data class EmailSignUpState(
    val emailValid: Boolean = false,
    val passwordValid: Boolean = false,
) {
    fun isInputValid(): Boolean {
        return emailValid && passwordValid
    }
}

There is a rule that forbids functions on data classrs

Why do you consider this function unnecessary?

hm, I think there are some use cases for functions, sometimes

That is true but to me this feels very nitpicky to prohibit this. How big is the performance impact really?

probably no performance gain. Maybe more like a code style choice. More compact and less brackets, dunno 🙂

But even if they are not final you can do the same using

val ... get()

. Any function without parameters can be replaced with a property

I guess it could still be a rule that is disabled by default, if my use case seems valid to you

To me it is not valid. I mean, I don't see any problem with that function. Probably I would write it as an extension function or extension property.