WeakSingleton.swift

class FancyString {
  let name: String
  
  init () { // Called one time
    print("init")
    name = "Frederik"
  }
  
  deinit { // Called one time
    print("deinit")
  }
}

class SharedString {
  static weak var weakInstance: FancyString?
  
  static var sharedInstance: FancyString? {
    get {
      if weakInstance == nil {
        let newInstance = FancyString()
        weakInstance = newInstance
        return newInstance
      } else {
        return weakInstance
      }
    }
  }
}

var str: FancyString? = SharedString.sharedInstance
var str2: FancyString? = SharedString.sharedInstance
var str3: FancyString? = SharedString.sharedInstance