struct Animal { let species: String init?(species: String) { if species.isEmpty { return nil } self.species = species } } //通过该可失败构造器来构建一个Animal的对象，并检查其构建过程是否成功 // someCreature 的类型是 Animal? 而不是 Animal let someCreature = Animal(species: "长颈鹿") // 打印 "动物初始化为长颈鹿" if let giraffe = someCreature { print("动物初始化为\(giraffe.species)") }