Mixing Partial KeyPaths and Arrays in Swift - arrays

Question

Apologies if this is trivial, but I have not yet gotten my head around KeyPaths fully. I have a class (ContainerClass) which has an array of classes in it (mySettings). the mySettings Class has two variables (color and name). The array of mySettings is defined at runtime. I am trying to modify the properties in the mySettings class via KeyPaths. The following code is a simplified version of what I am trying to achieve:
import Cocoa
import Foundation
class Settings {
var color: Int?
var name: String?
init(color: Int, name: String) {
self.color = color
self.name = name
}
}
class ContainerClass {
var mySettings = [Settings]()
}
var myClass = ContainerClass()
let kp = \ContainerClass.mySettings
let kp2 = [\Settings.color, \Settings.name]
myClass.mySettings.append(Settings(color: 1, name: "One"))
myClass.mySettings.append(Settings(color: 2, name: "Two"))
myClass.mySettings.append(Settings(color: 3, name: "Three"))
myClass.mySettings.append(Settings(color: 4, name: "Four"))
myClass.mySettings.append(Settings(color: 5, name: "Five"))
for index in 0..<myClass.mySettings.count {
print(myClass.mySettings[index].color!)
}
let target = myClass[keyPath: kp][0][keyPath: kp2[0]]
print("\ntarget:", target as! Int)
myClass[keyPath: kp][0][keyPath: kp2[0]] = 128 // ERROR: Cannot assign through subscript: 'myClass' is immutable
for index in 0..<myClass.mySettings.count {
print(myClass.mySettings[index].color!)
}
I need two separate KeyPaths: one to target one specific mySettings element of the array contained in ContainerClass, and another KeyPath to target one of the two properties within the Settings class. At runtime, the program will determine which element of the array and which property must be modified.
I can read the property (in my example via: let target = myClass[keyPath: kp][0][keyPath: kp2[0]]), but I cannot modify it by trying, for example, a line like: myClass[keyPath: kp][0][keyPath: kp2[0]] = 128. I get an error: Cannot assign through subscript: 'myClass' is immutable.
I am not sure about the interaction of these partial keypaths with arrays. Any help on how to resolve this (i.e. being able to modify properties within Settings this way) will be much appreciated.