Crashed on iPhone5(c)

AppDelegate.swift

import UIKit

struct Thing1 {
    let date: Date = Date()
    let string: String = String()
}

struct Thing2 {
    let block1 = Thing1()
    let block2 = Thing1()
    let block3 = Thing1()
    let block4 = Thing1()
}

struct Thing3 {
    let block1 = Thing2()
    let block2 = Thing2()
    let block3 = Thing2()
    let block4 = Thing2()
}

struct Thing4 {
    let block1 = Thing3()
    let block2 = Thing3()
    let block3 = Thing3()
    let block4 = Thing3()

    let test1 = Thing3()
    let test2 = Thing2()
    let test3 = Thing1()
    let test4 = Int32()
    let test5 = Int32()
    let test6 = Int32()
    let test7 = Int32()
    let test8 = Int32()
    let test9 = Int8()
}

enum TheEnum {
    case anotherCase
    case item(Thing4)
}

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        let item = TheEnum.item(Thing4())
        print(item)

        return true
    }
}