As I know Java is pass-by-value from this post. I am from Java background I wonder what Kotlin is using for passing values in between. Like in Extensions or Methods etc.
It uses the same principles like Java. It is always pass-by-value, you can imagine that a copy is passed. For primitive types, e.g. Int this is obvious, the value of such an argument will be passed into a function and the outer variable will not be modified. Please note that parameters in Kotlin cannot be reassigned since they act like vals:
fun takeInt(a: Int) {
a = 5
}
This code will not compile because a cannot be reassigned.
For objects it's a bit more difficult but it's also call-by-value. If you call a function with an object, a copy of its reference is passed into that function:
data class SomeObj(var x: Int = 0)
fun takeObject(o: SomeObj) {
o.x = 1
}
fun main(args: Array<String>) {
val obj = SomeObj()
takeObject(obj)
println("obj after call: $obj") // SomeObj(x=1)
}
You can use a reference passed into a function to change the actual object.