Swift 4 JSONDecoder复杂数据缺少关键字

struct Person: Codable {
    let name: String
    let age: Int
}

let json = """
{
    "name": "John"
}
"""

let jsonData = json.data(using: .utf8)!

do {
    let decoder = JSONDecoder()
    let person = try decoder.decode(Person.self, from: jsonData)
    
    // 处理解码后的person对象
    print(person.name) // 输出: John
    print(person.age) // 输出: 0 (默认值)
} catch {
    print("解码失败: \(error)")
}

struct Address: Codable {
    let street: String
    let city: String
}

struct Person: Codable {
    let name: String
    let age: Int
    let address: Address?
}

let json = """
{
    "name": "John",
    "age": 30
}
"""

let jsonData = json.data(using: .utf8)!

do {
    let decoder = JSONDecoder()
    let person = try decoder.decode(Person.self, from: jsonData)
    
    // 处理解码后的person对象
    print(person.name) // 输出: John
    print(person.age) // 输出: 30
    print(person.address) // 输出: nil (缺少关键字)
} catch {
    print("解码失败: \(error)")
}