kotlin: extracting from list - list

Question

I have a list of Int items say
Now I want to call a function process(item1, item2, item3, item4)
How can I do this in kotlin.
I want to pass how much ever items are present in the list to the method. The method accepts variable number of arguments
I want to call this method from firbase mlk library
public FirebaseVisionBarcodeDetectorOptions.Builder
setBarcodeFormats(#BarcodeFormat int var1, #BarcodeFormat int... var2) {
}
So I need to call setBarcodeFormats(is there a way in kotlin to pass each element of list as an arg here)

Answer 1

Based on the description of your problem I assume you have one method that takes a variable number of integers – let's call it fun foo(vararg n: Int).
If that's the case, than the bytecode that gets generated is the following:
public final static varargs foo([I)V
This means the method takes an array of int, which is an IntArray in Kotlin world.
In order to call that method with an IntArray you need to do:
fun foo(vararg n: Int) {
n.forEach(::println) // do something with n
}
fun main() {
val numbers = intArrayOf(1, 2, 3, 4)
foo(*numbers) // prints 1; 2; 3; 4
}
In that snippet of code, * is the spread operator and is briefly described here.
Also note that the spread operator can only be applied to arrays, so if you have a list of Int you need to convert it to an IntArray first an then apply the spread operator, like this:
fun foo(vararg n: Int) {
n.forEach(::println) // do something with n
}
fun main() {
val numbers = listOf(1, 2, 3, 4)
foo(*numbers.toIntArray()) // prints 1; 2; 3; 4
}
EDIT
Following the update to your question, you can call that method from your Kotlin code like this:
val builder = ... // obtain a Builder instance
val args = intArrayOf(1, 2, 4, 10)
builder.setBarcodeFormats(1, *args) // or any other meaningful value

Answer 2

You have two ways. First is pass a List of Int to the method. second is using varargs. For example a function which takes n number as inputs and returns the average of all the inputs. If we want to use List it will be like so:
fun getAverage(numbersList: List<Int>): Float {
var sum = 0.0f
for (item in numbersList) {
sum += item
}
return (sum / numbersList.size)
}
val arrayList = arrayListOf(1, 2, 3, 4)
val result = getAverage(arrayList)
And if we want to pass numbers as infinite function parameters we could do it with varargs like this:
fun getAverage(vararg input: Int): Float {
var sum = 0.0f
for (item in input) {
sum += item
}
return (sum / input.size)
}
val result1 = getAverage(1, 2, 3)
val result2 = getAverage(1, 2, 3, 4, 5)