Ios PropertyWrapper 不存在的 Codable 属性的默认值

我创建了一个属性包装器，如下所示:

@propertyWrapper
public struct DefaultTodayDate: Codable {
    public var wrappedValue: Date

    private let dateFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.dateFormat = "y-MM-dd'T'HH:mm:ss"

        return formatter
    }()

    public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        var stringDate = ""
        do {
            stringDate = try container.decode(String.self)
            self.wrappedValue = self.dateFormatter.date(from: stringDate) ?? Date()
        } catch {
            self.wrappedValue = Date()
        }
    }

    public func encode(to encoder: Encoder) throws {
        try wrappedValue.encode(to: encoder)
    }
}

还有一个这样的模型:

struct MyModel: Codable {
    @DefaultTodayDate var date: Date
}

因此，如果我想要解析这个json文件，一切都很正常:

let json = #"{ "date": "2022-10-10T09:09:09" }"#.data(using: .utf8)!
let result = try! JSONDecoder().decode(MyModel.self, from: json)

print(result) // result.date is: 2022-10-10 09:09:09 +0000
-----

let json = #"{ "date": "" }"#.data(using: .utf8)!
let result = try! JSONDecoder().decode(MyModel.self, from: json)

print(result) // result.date is: Date()
-----

let json = #"{ "date": null }"#.data(using: .utf8)!
let result = try! JSONDecoder().decode(MyModel.self, from: json)

print(result) // result.date is: Date()

但是我也想解析一个没有date个属性的JSON.致命错误:

let json = #"{ "book": "test" }"#.data(using: .utf8)!
let result = try! JSONDecoder().decode(MyModel.self, from: json)

// Fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.keyNotFound(CodingKeys(stringValue: "date", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"date\", intValue: nil) (\"date\").", underlyingError: nil))

print(result) // i want to result.date be Date()