How bad is it if

val

property doesn't always return the same value? Say it has a getter, and does some computation on other mutable parts of the class. Is it horrible? Amazingly bad?

I would make this a function to make it clear to consumers that it’s calculated

yeah, that definitely seems like the smarter choice!

It's not bad, considering there's plenty of existing usage of non-constant

val

properties even in the Kotlin API itself, such as

List.size

.

I agree that it is not bad as long as it only changes when some property of the object changes, like

List.size

. If it is something that is calculated randomly or has side effects, then being a

val

would be bad.

https://kotlinlang.org/docs/reference/coding-conventions.html#functions-vs-properties

Prefer a property over a function when the underlying algorithm:

• does not throw

• is cheap to calculate (or cached on the first run)

• returns the same result over invocations if the object state hasn't changed

so if it returns a different value without state changes, it's recommended not to use a

val