protocol Proto {} class Cat : Proto { func nya() { print("nyaa") } } extension Proto { func exec2(f: (Self) -> Void) { f(self) } } let cat = Cat() cat.exec2 { $0.nya() }protocol Proto {} class Cat : Proto { func nya() { print("nyaa") } } extension Proto { func exec2(f: (Self) -> Void) { f(self) } } let cat = Cat() cat.exec2 { $0.nya() }