Swift 4可解码，动态密钥未知

要解码任意字符串，您需要这样的密钥：

// Arbitrary key
private struct Key: CodingKey, Hashable, CustomStringConvertible {
static let meta = Key(stringValue: "Meta")!
var description: String {
return stringValue
}
var hashValue: Int { return stringValue.hash }
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 }
}

这是一个非常通用的工具(static let meta除外(，可以用于所有类型的通用关键问题。

这样，您就可以找到第一个不是.meta的密钥，并将其用作动态密钥。

public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: Key.self)
meta = try container.decode([String: String].self, forKey: .meta)
guard let dynamicKey = container.allKeys.first(where: { $0 != .meta }) else {
throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: [],
debugDescription: "Could not find dynamic key"))
}
unknown = try container.decode(Double.self, forKey: dynamicKey)
}

一起作为游乐场：

import Foundation
let json = Data("""
{"DynamicKey":6410,"Meta":{"name":"","page":""}}
""".utf8)
public struct MyStruct: Decodable {
public let unknown: Double
public let meta: [String: String]
// Arbitrary key
private struct Key: CodingKey, Hashable, CustomStringConvertible {
static let meta = Key(stringValue: "Meta")!
var description: String {
return stringValue
}
var hashValue: Int { return stringValue.hash }
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 }
}
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: Key.self)
meta = try container.decode([String: String].self, forKey: .meta)
guard let dynamicKey = container.allKeys.first(where: { $0 != .meta }) else {
throw DecodingError.dataCorrupted(.init(codingPath: [],
debugDescription: "Could not find dynamic key"))
}
unknown = try container.decode(Double.self, forKey: dynamicKey)
}
}

let myStruct = try! JSONDecoder().decode(MyStruct.self, from: json)
myStruct.unknown
myStruct.meta

此技术可以扩展为解码任意JSON。有时这样做更容易，然后取出你想要的片段，然后解码每一个片段。例如，使用上面的JSON要点，可以通过以下方式实现MyStruct：

public struct MyStruct: Decodable {
public let unknown: Double
public let meta: [String: String]
public init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
let json = try container.decode(JSON.self)
guard let meta = json["Meta"]?.dictionaryValue as? [String: String] else {
throw DecodingError.dataCorrupted(.init(codingPath: [],
debugDescription: "Could not find meta key"))
}
self.meta = meta
guard let (_, unknownJSON) = json.objectValue?.first(where: { (key, _) in key != "Meta" }),
let unknown = unknownJSON.doubleValue
else {
throw DecodingError.dataCorrupted(.init(codingPath: [],
debugDescription: "Could not find dynamic key"))
}
self.unknown = unknown
}
}