I know that val cannot be reassigned, but how woul...

# getting-started

[oday]

I know that val cannot be reassigned, but how would I for example send a variable to a function to do something with it?

private fun resetCounterAndGame(counter: Int) {
    if (counter == 2) {
        gameButtonText.set(resProvider.getString(R.string.try_another_number))
        gameStarted = false
        counter = 0 <--- val cannot be reassigned of course
    }
}

[wbertan]

Can you make it return the new value for counter?

[oday]

yea sure I can, but then I would be doing thingImTryingToCount = resetGameAndCounter(thingImTryingToCount)

[oday]

right?

[oday]

yea cause I wanna do this for several counters

[oday]

I think the function is doing too much

[oday]

I can have an extension function that can be like counter.reset() and if this == 2 return 0 else return this

[wbertan]

Could you use a MutableStateFlow instead? So you can pass the reference and set a new value, and whenever reads the state flow would always pick the latest value.

[oday]

hm im not really using coroutines right now

[oday]

ill check it out

[Vampire]

Your problem is not so much that val cannot be reassigned, but that you confuse pass-by-value and pass-by-reference.

[Vampire]

You don't push a variable to the method, but only its value

[Vampire]

In case of an object you are passing the reference to that object in and can modify the state of that object

[Vampire]

But for an Int you just pass the 2

[Vampire]

You can probably do something like this:

private fun resetCounterAndGame(counter: KMutableProperty<Int>) {
    if (counter.getter.call() == 2) {
        gameButtonText.set(resProvider.getString(R.string.try_another_number))
        gameStarted = false
        counter.setter.call(0)
    }
}

and then pass the reference to the field with resetCounterAndGame(::counter) or similar, but I would strongly advice to not do this.

[Tobias Berger]

there are some ways you could do this.
• you could return an object containing all the new values you want to set and do so after the function call
• you could pass setter callbacks to the functions that set a new value when called
• you can wrap the mutable values in an object that is passed to the function and then modified inside
Depending on your use case, each of these can be the perfect solution or a real code smell.

[Tobias Berger]

actuall I also thougt of the KMutablePropert approach. I wouldn't sa it's a no-go, especially since reflection in Kotlin offers a lot more type safety than in Java. But it can still have some performance impact which might be undesireable in a mobile application and also it would only work with properties, not with local variables.

[Vampire]

Yeah, probably better to give a setter instead of using reflection, but still a bit smelly 😄

private fun resetCounterAndGame(counter: Int, counterSetter: (Int) -> Unit) {
    if (counter == 2) {
        counterSetter(0)
    }
}

fun main() {
    var counter = 1
    println(counter)
    resetCounterAndGame(counter++) { counter = it }
    println(counter)
    resetCounterAndGame(counter++) { counter = it }
    println(counter)
}

=>

1
2
0

[Kirill Grouchnikov]

Ah, the good old Fortran days where you could pass "4" as an integer argument, and then the function could override its value to 5. Then after the function returns, everywhere you had 4 was treated as 5. Yeah, you don't want that.

[Ryan]

use an AtomicInt