AnyDecodable

AnyDecodable.swift

import Foundation


struct AnyDecodable: Decodable {
    static let supportedTypes = CodingUserInfoKey(rawValue: "SupportedTypes")!
    
    enum Errors: Error {
        case missingSupportedTypesList
        case unknownType
    }
    
    typealias DecodableValue = Any & Decodable
    let value: DecodableValue
    
    init(from decoder: Decoder) throws {
        guard let supportedTypes = decoder.userInfo[AnyDecodable.supportedTypes] as? [Any.Type] else {
            throw Errors.missingSupportedTypesList
        }
        
        let decodableTypes = supportedTypes.compactMap { $0 as? Decodable.Type }

        var decodedValue: DecodableValue?
        for decodableValueType in decodableTypes {
            do {
                decodedValue = try decodableValueType.init(from: decoder)
                break
            } catch {
                continue
            }
        }
        guard let v = decodedValue else {
            throw Errors.unknownType
        }
        value = v
    }
}


struct Person: Codable {
    let name: String
}

struct Dog: Codable {
    let breed: String
}

let decoder = JSONDecoder()
decoder.userInfo[AnyDecodable.supportedTypes] = [Person.self, Dog.self]
let p = try decoder.decode(AnyDecodable.self, from: "{\"name\":\"Joe\"}".data(using: .utf8)!).value
print(p) // Person(name: "Joe")

let d = try decoder.decode(AnyDecodable.self, from: "{\"breed\":\"Caniche\"}".data(using: .utf8)!).value
print(d) // Dog(breed: "Caniche")