Static imports in Java are not “bad”. Static mutable state can cause problems. Kotlin helps one avoi...

# announcements

[natpryce]

Static imports in Java are not “bad”. Static mutable state can cause problems. Kotlin helps one avoid mutable state, with an emphasis on immutable data and pure functions.

[Andrew Gazelka]

I heard stateful static functions are bad. What if the state is stored in an object? i.e.,

object Test {
  val list = arrayListOf("a","b","c")
}

fun testerSomething() = Test.list.joinToString()

[Andrew Gazelka]

having the function out of the object is esp nice for extension functions

[natpryce]

The state in that example is still global.

[natpryce]

But yes, global mutable state is often problematic

[natpryce]

But Kotlin’s extension functions do not, by themselves, give you mutable state.

[Andrew Gazelka]

so it would be bad to have
fun testerAdd() = Test.list.add("something")
i.e., for some type of manager class

[natpryce]

Yes. In that case, the Test object is a mutable singleton.

[natpryce]

That doesn’t encapsulate it’s (global) mutable state

[natpryce]

My point is: it’s not the testerAdd function that’s the problem, it’s the Test object.

[Andrew Gazelka]

oh I see because list should be private if it is in a class/object

[natpryce]

I’d say that Test should be immutable.

[Andrew Gazelka]

well this would be for a manager class where I would have
fun add(stored: Something)
fun update(stored: Something)
fun remove(stored: Something)
fun get(id: String): Something?
so it would need to be mutable

[natpryce]

Then I’d advise against making it a global singleton.

[Andrew Gazelka]

instead make the storage map private and have all those functions as part of the object?

[natpryce]

Don’t make it an object declaration

[Andrew Gazelka]

oh so the map would not be in a class

[Andrew Gazelka]

(or an object)

[natpryce]

I mean… don’t make it an object declaration. Define a class. Pass references to instances of that class around. That way, you can control the how the mutability affects different parts of the system explicitly.

[Andrew Gazelka]

ok thanks