Swift initialize stored property issue

Question

I have a class

class Service: NSObject {
  let wirlessSerivce: WirlessSerivce

  override init()
  {
    super.init()
    wirlessSerivce = WirlessSerivce()
    wirlessSerivce.delegate.addDelegate(self)
  }
}

I got these two issues:

1. Property 'self.wirlessSerivce' not initialized at super.init call

2. Immutable value 'self.wirlessSerivce' may only be initialized once (change let to var)

The goal I want to achieve is create wirlessSerivce and subscribe Service class to wirlessSerivce updates via delegate. I use multicast delegate and want to notify my Service if some data changes in wirlessSerivce

Also can I do something like this:

 class Service: NSObject {
      let wirlessSerivce =  WirlessSerivce() {
        didSet {
          wirlessSerivce.delegate.addDelegate(self)
        }
}

As I understood let wirlessSerivce = WirlessSerivce() will create an instance even before class gets its initialize method. Right?

Seems this code works:

class Service: NSObject {
  var wirlessSerivce: WirlessSerivce!

  override init()
  {
    super.init()
    wirlessSerivce = WirlessSerivce()
    wirlessSerivce.delegate.addDelegate(self)
  }
}

but here are few issues: var is for mutable properties and I don't need mutable service actually. (!) says that instance will be initialized before use it from anywhere. But I initialize it in init func, do I really need to mark it with (!)