Update object inside a list Kotlin - kotlin

Question

I am trying to modify my allVehicles variable, so it should contain the problem information that's in the vehiclesWithProblems list.
This is a simplified version of my code, but I need an updated allVehicles list that contains the replacement and remove the old one (the one without the problem).
How could I achieve that? This code is not working, the allVehicles list remains unchanged.
data class VehicleContainer(
val id: Int,
val vehicles: List<Vehicle>
)
data class Vehicle(
val id: Int,
val name: String,
val problem: Problem
)
data class Problem(
val quantity: Int,
val problemList: List<Int>,
val info: String? = ""
)
fun main() {
val vehiclesWithProblems = listOf<Vehicle>() //list of vehicles with problems - wont be empty
val allVehicles = mutableListOf<Vehicle>()//list of all vehicles (initially without any problems, but won't be empty either)
allVehicles.forEachIndexed { index, vehicle ->
val newVehicle = vehiclesWithProblems.find { vehicleWithProblem -> vehicle.id == vehicleWithProblem.id }
if (newVehicle != null) {
val replacement = vehicle.copy(problem = Problem(
quantity = newVehicle.problem.quantity,
problemList = newVehicle.problem.problemList,
info = newVehicle.problem.info)
)
allVehicles[index] = replacement
}
}
}

Answer 1

Seems to me the allVehicles list is actually modified, but beware! You make a copy of the vehicle where only the problem is changed, the rest remains unchanged. Runn the underneath code and you will see that after looping, the «Tesla without a problem» is still in the list, but now with a problem (so the list actually is changed.):
fun main() {
val vehiclesWithProblems = listOf(Vehicle(1, "Tesla", Problem(1, listOf(1), "Problem #1"))) //list of vehicles with problems - wont be empty
val allVehicles = mutableListOf(Vehicle(1, "Tesla without a problem", Problem(0, listOf(0), "No problem")))//list of all vehicles (initially without any problems, but won't be empty either)
println("vehiclesWithProblems: $vehiclesWithProblems")
println("allVehicles: $allVehicles")
allVehicles.forEachIndexed { index, vehicle ->
val newVehicle = vehiclesWithProblems.find { vehicleWithProblem -> vehicle.id == vehicleWithProblem.id }
if (newVehicle != null) {
val replacement = vehicle.copy(problem = Problem(
quantity = newVehicle.problem.quantity,
problemList = newVehicle.problem.problemList,
info = newVehicle.problem.info)
)
println("Changing #$index!")
allVehicles[index] = replacement
}
}
println("After the loop, allVehicles: $allVehicles")
}