@swiftbot
struct Stone {} class Cat { init() { print("init cat") } deinit { print("deinit cat") } func nya() { print("begin nya") var stone = Stone() { didSet { self.mofu(stone) } } stone = Stone() print("end nya") } func mofu(_ stone: Stone) { print("mofu") } } func main() { var cat = Cat() cat.nya() } main()