Decodable 非常强大。它可以完全解码任意 JSON，所以这只是该问题的一个子集。如需完整的 JSON Decodable，请参阅此 JSON。
我将从示例中提取Key 的概念，但为简单起见，我假设值必须是Int 或String。您可以将 parameters 设为 [String: JSON] 并改用我的 JSON 解码器。
struct Model: Decodable {
let name: String
let number: Int
let params: [String: Any]
// An arbitrary-string Key, with a few "well known and required" keys
struct Key: CodingKey, Equatable {
static let name = Key("name")
static let number = Key("number")
static let knownKeys = [Key.name, .number]
static func ==(lhs: Key, rhs: Key) -> Bool {
return lhs.stringValue == rhs.stringValue
}
let stringValue: String
init(_ string: String) { self.stringValue = string }
init?(stringValue: String) { self.init(stringValue) }
var intValue: Int? { return nil }
init?(intValue: Int) { return nil }
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: Key.self)
// First decode what we know
name = try container.decode(String.self, forKey: .name)
number = try container.decode(Int.self, forKey:. number)
// Find all the "other" keys
let optionalKeys = container.allKeys
.filter { !Key.knownKeys.contains($0) }
// Walk through the keys and try to decode them in every legal way
// Throw an error if none of the decodes work. For this simple example
// I'm assuming it is a String or Int, but this is also solvable for
// arbitarily complex data (it's just more complicated)
// This code is uglier than it should be because of the `Any` result.
// It could be a lot nicer if parameters were a more restricted type
var p: [String: Any] = [:]
for key in optionalKeys {
if let stringValue = try? container.decode(String.self, forKey: key) {
p[key.stringValue] = stringValue
} else {
p[key.stringValue] = try container.decode(Int.self, forKey: key)
}
}
params = p
}
}
let json = Data("""
{
"name": "Some name",
"number": 42,
"param0": 1,
"param1": "2",
"param2": 3
}
""".utf8)
try JSONDecoder().decode(Model.self, from: json)
// Model(name: "Some name", number: 42, params: ["param0": 1, "param1": "2", "param2": 3])
其他想法
我认为下面的 cmets 非常重要，未来的读者应该仔细阅读它们。我想展示需要多少代码重复，以及其中多少可以轻松提取和重用，这样就不需要魔法或动态特性。
首先，提取常用且可重复使用的部分：
func additionalParameters<Key>(from container: KeyedDecodingContainer<Key>,
excludingKeys: [Key]) throws -> [String: Any]
where Key: CodingKey {
// Find all the "other" keys and convert them to Keys
let excludingKeyStrings = excludingKeys.map { $0.stringValue }
let optionalKeys = container.allKeys
.filter { !excludingKeyStrings.contains($0.stringValue)}
var p: [String: Any] = [:]
for key in optionalKeys {
if let stringValue = try? container.decode(String.self, forKey: key) {
p[key.stringValue] = stringValue
} else {
p[key.stringValue] = try container.decode(Int.self, forKey: key)
}
}
return p
}
struct StringKey: CodingKey {
let stringValue: String
init(_ string: String) { self.stringValue = string }
init?(stringValue: String) { self.init(stringValue) }
var intValue: Int? { return nil }
init?(intValue: Int) { return nil }
}
现在，Model 的解码器被简化为这个
struct Model: Decodable {
let name: String
let number: Int
let params: [String: Any]
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: StringKey.self)
name = try container.decode(String.self, forKey: StringKey("name"))
number = try container.decode(Int.self, forKey: StringKey("number"))
params = try additionalParameters(from: container,
excludingKeys: ["name", "number"].map(StringKey.init))
}
}
如果有一些神奇的方式可以说“请以默认方式处理这些属性”，那就太好了，但坦率地说，我不太清楚那会是什么样子。这里的代码量与实现NSCoding的代码量差不多，比实现NSJSONSerialization的代码量少得多，如果太繁琐的话很容易交给swiftgen（基本上是你必须为@987654335编写的代码@)。作为交换，我们获得了完整的编译时类型检查，因此我们知道当我们遇到意外情况时它不会崩溃。
有几种方法可以使上述内容更短一些（我目前正在考虑涉及 KeyPaths 的想法，以使其更加方便）。关键是当前的工具非常强大，值得探索。