似乎decode(_forKey:)
忽略了它的第一个参数,而是依赖泛型参数来决定要解码的类型。如果是这种情况,第一个参数是什么?
class Cat: Codable {
func speak() -> String { return "Meow" }
}
class Lion: Cat {
override func speak() -> String { return "Roar!" }
}
class Person: Codable {
let firstPet: Cat
let secondPet: Cat
init(firstPet: Cat, secondPet: Cat) {
self.firstPet = firstPet
self.secondPet = secondPet
}
enum CodingKeys: CodingKey { case firstPet, secondPet }
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.firstPet = try container.decode(Lion.self, forKey: .firstPet)
let typeOfCat: Cat.Type = Lion.self
self.secondPet = try container.decode(typeOfCat, forKey: .secondPet)
}
}
let before = Person(firstPet: Lion(), secondPet: Lion())
let after = try! JSONDecoder().decode(Person.self, from: JSONEncoder().encode(before))
after.firstPet.speak() //"Roar!"
after.secondPet.speak() //"Meow" ...really?