拡張クラスに保存

UIViewControllerを拡張して、StringやBoolが保存できる

vc.addedString = "Str" vc.addedBool = true

public extension UIViewController {
    private struct additional {
        static var addedString: String = ""
        static var addedBool: Bool = false
        // TODO: ここ他にも増やせる
    }

    var addedString: String {
        get {
            guard let theString = objc_getAssociatedObject(self, &additional.addedString) as? String else {
                return ""
            }
            return theString
        }
        set {
            objc_setAssociatedObject(self, &additional.addedString, newValue, .OBJC_ASSOCIATION_RETAIN)
        }
    }

    var addedBool: Bool {
        get {
            guard let theBool = objc_getAssociatedObject(self, &additional.addedBool) as? Bool else {
                return false
            }
            return theBool
        }
        set {
            objc_setAssociatedObject(self, &additional.addedBool, newValue, .OBJC_ASSOCIATION_RETAIN)
        }
    }

     // TODO: ここ他にも増やせる
}