Decoding heterogeneous array in swift

Decode.swift

import Foundation

struct User {
    let name: String
    let age: Int
}
struct Car {
    let color: String
}

enum Entry {
    case user(User)
    case car(Car)
}

typealias Json = Any
typealias JsonDict = [String: Json]

protocol Decodable {
    init(json: Json) throws
}
enum JsonMappingError: ErrorType {
    case WrongType
    case MissingField
    case UnknownType
}
extension User: Decodable {
    init(json: Json) throws {
        guard let dict = json as? JsonDict else {
            throw JsonMappingError.WrongType
        }
        guard let name = dict["name"] as? String,
            age = dict["age"] as? Int else {
            throw JsonMappingError.MissingField
        }
        self.name = name
        self.age = age
    }
}

extension Car: Decodable {
    init(json: Json) throws {
        guard let dict = json as? JsonDict else {
            throw JsonMappingError.WrongType
        }
        guard let color = dict["color"] as? String else {
            throw JsonMappingError.MissingField
        }
        self.color = color
    }
}

protocol TypedDecodable: Decodable {
    init(type: String, dict: JsonDict) throws
}
extension TypedDecodable {
    init(json: Json) throws {
        guard let dict = json as? JsonDict else {
            throw JsonMappingError.WrongType
        }
        guard let type = dict["type"] as? String else {
            throw JsonMappingError.MissingField
        }
        try self.init(type: type, dict: dict)
    }
}

protocol EnumTypedDecodable: TypedDecodable {
    static var typeMap: [String: (Json throws -> Self)] { get }
}

extension EnumTypedDecodable {
    init(type: String, dict: JsonDict) throws {
        guard let creator = Self.typeMap[type] else {
            throw JsonMappingError.UnknownType
        }
        self = try creator(dict)
    }
}

extension Entry: EnumTypedDecodable {
    static var typeMap: [String: (Json throws -> Entry)] = [
        "user": { .user(try User(json: $0)) },
        "car": { .car(try Car(json: $0)) },
    ]
}

let json: [JsonDict] = [
    ["type": "car", "color": "blue"],
    ["type": "user", "name": "John", "age": 30]
]
try json.map(Entry.init)