如何使用 Swift Codable 框架拒绝意外的 JSON 数据（键）

Question

我很好奇，有没有办法拒绝任意数据被Swift中的JSONDecoder忽略？即使手动实施

init(decoder:)

，我也看不到捕捉意外键的方法。我试过了，但在那里找不到答案。有人可以指出我正确的方向吗？例如，我可以在某处设置一个解码策略标志来帮助解决这个问题吗？

这里有一些代码来显示问题（如果

importData

被调用，预计会出现致命错误）：

private struct DataRecord {
    var greeting: String = "Hello"
}

// Adding Codable in an extension allows us to keep the compiler generated init().
extension DataRecord: Codable {
    enum CodingKeys: CodingKey, CaseIterable {
        case greeting
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)

        try container.encode(greeting, forKey: .greeting)
    }
        
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        greeting = try container.decode(String.self, forKey: .greeting)
        
        // An attempt at rejecting unrecognised keys, but allKeys doesn't include "unexpected_key"
        let foundKeys = Set(container.allKeys.map { $0.stringValue })
        let validKeys = Set(CodingKeys.allCases.map { $0.stringValue })
        let invalidKeys = foundKeys.subtracting(validKeys)
        
        print("found: \(foundKeys)")
        print("valid: \(validKeys)")
        print("invalid: \(invalidKeys)")
        
        guard invalidKeys.isEmpty else {
            fatalError("Bad Keys Found: \(invalidKeys)")
        }
    }
}

func importData() {
    let stringData = """
{
    "greeting": "Hello World!",
    "unexpected_key": "This should fail!"
}
"""
    let data = stringData.data(using:.utf8)!
    let decoder = JSONDecoder()
    
    let record = try! decoder.decode(DataRecord.self, from: data) // <-- this should fail
}