Method returns tuples in Kotlin - kotlin

Question

I don't see any examples of how to use tuples in Kotlin.
The errors i get on the first line (method definition) is "unresolved reference: a" and "expecting member declaration" for Int...
private fun playingAround : Pair<out a: Int, out b: Int> {
if(b != 0) {
b = a
a = a * 2
} else {
b = a
a = a * 3
}
return Pair(a, b)
}
About the logic: b is 0 in the beginning and a has a random value.
From the second call on, we go into the else logic.
i don't feel the official doc is enough: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-pair/index.html. I did try also without the ":" after the method name like the official doc seems to imply
-same problem

Answer 1

You are using incorrect syntax. It should be something like this:
private fun playingAround(a: Int, b: Int): Pair<Int, Int> {
val x: Int
val y: Int
if (b != 0) {
y = a
x = a * 2
} else {
y = a
x = a * 3
}
return Pair(x, y)
}
Note that a and b are method parameter values which cannot be reassigned, so you need variables x and y to store the result.
You can write this with much shorter syntax though:
private fun playingAround(a: Int, b: Int) = if (b != 0) Pair(a * 2, a) else Pair(a * 3, a)

Answer 2

Please have a look at the functions chapter of the kotlin reference and/or play around with the Kotlin koans to get familiar with Kotlin (or if, by any means, reading grammar is your favorite, have a look at the function declaration grammar instead; if you do not get what's written there, no problem. Start with the tutorials/reference instead).
One of the solutions could look like this:
private fun playingAround(a: Int, b: Int) = b.let {
if (it != 0) a * 2
else a * 3
} to a
or if you meant, that you actually want to pass a pair, then maybe the following is better:
private fun playingAround(givenPair: Pair<Int, Int>) = givenPair.let { (a, b) ->
b.let {
if (it != 0) a * 2
else a * 3
} to a
}
It's hard to really know what you wanted to accomplish as you didn't really specify what that is.
Extension function instead? For completeness:
private fun Pair<Int, Int>.playingAround() = let { (a, b) ->
b.let {
if (it != 0) a * 2
else a * 3
} to a
}
and of course: you do not need to use let, nor to use to, nor to use destructuring declarations, etc. There are just some of many possible solutions.

Answer 3

You can rewrite your code as the following:
private fun playingAround(a: Int, b: Int) : Pair<Int, Int> {
val tempA: Int
val tempB: Int
if(b != 0) {
tempB = a
tempA = a * 2
} else {
tempB = a
tempA = a * 3
}
return Pair(tempA, tempB)
}
And using Destructuring Declarations you can write the following:
val (a, b) = playingAround(1, 2)

Answer 4

Your function syntax is not correct. I suggest to study the documentation first.
To make this a bit more Kotlin-idiomatic, use if as an expression:
private fun playingAround(a: Int, b: Int): Pair<Int, Int> =
if (b != 0) {
Pair(a * 2, a)
} else {
Pair(a * 3, a)
}