For context: I'm using kotlin multiplatform to communicate with my backend for my both apps, I'm also trying to follow Clean Architecture + MVVM.
My multiplatform project holds my data layer (repositories and dtos) and my app project holds the presentation and domain layer (VC, View Model, Use Case).
I'm trying to do is mock my repository in the multiplatform project.
I have a class (DTO) on my Kotlin Multiplatform project that looks like this
#Serializable
data class LoginResponse(val data: LoginResponseBody){
#Serializable
data class LoginResponseBody(
var accessToken: String,
var lastChannel: String? = null,
var lastDateTime: String? = null,
var userId: String? = null,
var transactionalKeyStatus: String? = null,
var accessStatus: String? = null
)
}
When I add that multiplatform project into my xcode project, the object translates to:
__attribute__((objc_subclassing_restricted))
__attribute__((swift_name("LoginResponse")))
#interface SharedEmaLoginResponse : SharedEmaBase
- (instancetype)initWithData:(SharedEmaLoginResponseLoginResponseBody *)data __attribute__((swift_name("init(data:)"))) __attribute__((objc_designated_initializer));
- (SharedEmaLoginResponseLoginResponseBody *)component1 __attribute__((swift_name("component1()")));
- (SharedEmaLoginResponse *)doCopyData:(SharedEmaLoginResponseLoginResponseBody *)data __attribute__((swift_name("doCopy(data:)")));
- (BOOL)isEqual:(id _Nullable)other __attribute__((swift_name("isEqual(_:)")));
- (NSUInteger)hash __attribute__((swift_name("hash()")));
- (NSString *)description __attribute__((swift_name("description()")));
#property (readonly) SharedEmaLoginResponseLoginResponseBody *data __attribute__((swift_name("data")));
#end;
I thought that class LoginResponse would conform to 'Decodable' but it doesn't, this is what my fake repository looks like in my xcode project
final class LoginRepositoryTest : XCTestCase, IAuthRepository {
var hasError = false
func login(loginRequest: LoginRequest, success: #escaping (LoginResponse) -> Void, failure: #escaping (ErrorResponse) -> Void, completionHandler: #escaping (KotlinUnit?, Error?) -> Void) {
if hasError {
failure(ErrorResponse(messages: []))
} else {
let data = loadStub(name: "loginResponse", extension: "json")
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .secondsSince1970
let loginData = try! decoder.decode(LoginResponse.self, from: data)
success(loginData)
}
}
func getKoin() -> Koin_coreKoin {}
}
Error
Instance method 'decode(_:from:)' requires that 'LoginResponse' conform to 'Decodable'
I think I have these two options:
I make that kotlin class conform to 'Decodable'
I find a way to convert that JSON to that object without using Decodable
Any help is appreciated
Kotlin serialization isn't meant to confirm Decodable protocol to the class. It's meant to be used from kotlin with kotlin serialization, like this:
val response: LoginResponse = Json.decodeFromString(
LoginResponse.serializer(),
string
)
p.s. originally you can use Json.decodeFromString<LoginResponse>(string), but this's not yet supported on multiplatform as far as I remember
Network and JSON parsing are things which are most easily done on KMM, and you can write tests there too, but in case you still need to use it directly from iOS, you can try the following wrapper:
object JsonHelper {
#Throws(Throwable::class)
fun decodeRtcMsg(string: String) =
Json.decodeFromString(
RtcMsg.serializer(),
string
)
}
Then you can use it from swift:
do {
try JsonHelper().decodeLoginResponse(string: "")
} catch {
print(error)
}
If you really need it to Decodable I'd create an expect/actual of Decodable for ex:
// in common
expect interface Decodable
// on Android
actual interface Decodable
// on iOS
actual typealias Decodable = Decodable
Then just implement Decodable for your DTOs. Perhaps the best example for this is how you could use the Parcelize in your shared code: https://github.com/icerockdev/moko-parcelize/blob/master/parcelize/src/androidMain/kotlin/dev/icerock/moko/parcelize/Parcelize.kt
Related
Introduction
(Apologies if the title is confusing, but I explain the question better here!)
I'm building a networking library that can perform JSON decoding on its responses.
Host apps adopting this library will create enums conforming to NetLibRoute. All that currently does is enforce the presence of asURL:
public protocol NetLibRoute {
var asURL: URL { get throws }
}
In a host app, I have a routing system that enforces API structure at the compiler-level (via enums and associated values) for each endpoint, like this:
enum Routes: NetLibRoute {
case people(Int?)
// Other routes go here, e.g.:
// case user(Int)
// case search(query: String, limit: Int?)
var asURL: URL {
let host = "https://swapi.dev/"
let urlString: String
switch self {
case let .people(personID):
if let personID {
urlString = host + "api/people/\(personID)"
} else {
urlString = host + "api/people/"
}
// Build other URLs from associated values
}
return URL(string: urlString)!
}
}
I also want each enum to be associated with a certain Codable type. I can do that, of course, by modifying the Route protocol declaration to also require a type conforming to Decodable:
protocol NetLibRoute {
var asURL: URL { get throws }
var decodedType: Decodable.Type { get } // This
}
And a matching computed property in my Routes enum:
var decodedType: Decodable.Type {
switch self {
case .people(_):
return Person.self
// And so on
}
}
The Problem
Currently, my networking code has a declaration something like this:
public static func get<T>(route: NetLibRoute,
type: T.Type) async throws -> T where T: Decodable {
// performing request on route.asURL
// decoding from JSON as T or throwing error
// returning decoded T
}
Which lets me call it like this:
let person = try await NetLib.get(route: Routes.people(1), type: Person.self)
However, this redundancy (and potential human error from mismatching route and type) really irks me. I really want to be able to only pass in a route, and have the resulting type be inferred from there.
Is there some way to get the compiler to somehow check the NetLibRoute enum and check its decodedType property, in order to know what type to use?
Ultimately, I want this networking function to take one parameter (a route) and infer the return type of that route (at compile-time, not with fragile runtime hacks or !s), and return an instance of the type.
Is this possible?
Potential Alternatives?
I'm also open to alternative solutions that may involve moving where the get function is called from.
For example, calling this get function on a route itself to return the type:
let person = try await Routes.people(1).get(type: Person.self) // Works, but not optimal
let person = try await Routes.people(1).get() // What I want
Or even on the type itself, by creating a new protocol in the library, and then extending Decodable to conform to it:
public protocol NetLibFetchable {
static var route: NetLibRoute { get }
}
extension Decodable where Self: NetLibFetchable {
public static func get<T>() async throws -> T where Self == T, T: Decodable {
// Call normal get function using inferred properties
return try await NetLib.get(route: route,
type: T.self)
}
Which indeed lets me call like this:
let person = try await Person.get() // I can't figure out a clean way to pass in properties that the API may want, at least not without once again passing in Routes.people(1), defeating the goal of having Person and Routes.people inherently linked.
While this eliminates the issue of type inference, the route can no longer be customized at call-time, and instead is stuck like this:
extension Person: NetLibFetchable {
public static var route: NetLibRoute {
Routes.people(1) // Can't customize to different ID Ints anymore!
}
}
Which makes this particular example a no-go, and leaves me at a loss.
Appreciation
Anyway, thank you so much for reading, for your time, and for your help.
I really want this library to be as clean as possible for host apps interacting with it, and your help will make that possible.
Are you wedded to the idea of using an enum? If not, you can do pretty much what you want by giving each enum value its own type and using an associated type to do what you want.
public protocol NetLibRoute
{
var asURL: URL { get throws }
associatedtype Decoded: Decodable
}
struct Person: Decodable
{
var name: String
}
struct Login: Decodable
{
var id: String
}
struct People: NetLibRoute
{
typealias Decoded = Person
var id: Int
var asURL: URL { return URL(filePath: "/") }
}
struct User: NetLibRoute
{
typealias Decoded = Login
var id: String
var asURL: URL { return URL(filePath: "/") }
}
func get<N: NetLibRoute>(item: N) throws -> N.Decoded
{
let data = try Data(contentsOf: item.asURL)
return try JSONDecoder().decode(N.Decoded.self, from: data)
}
let thing1 = try get(item: People(id: 1))
let thing2 = try get(item: User(id: "foo"))
Where you might have had a switch before to do different things with different Routes you would now use a function with overloaded arguments.
func doSomething(thing: Person)
{
// do something for a Person
}
func doSomething(thing: Login)
{
// do something else for a Login
}
doSomething(thing: thing1)
doSomething(thing: thing2)
I think the problem lays in this function.
public static func get<T>(route: Route,
type: T.Type) async throws -> T where T: Decodable {
// performing request on route.asURL
// decoding from JSON as T or throwing error
// returning decoded T
}
On the first hand, it uses concretions instead of abstractions. You shouldn't pass a Route here, it should use your protocol NetLibRoute instead.
On the other hand, I think that the type param is not needed. Afaik you can get the Type to Decode with the var:
NetLibRoute.decodedType
Am I missing something on this matter?
Apart from that, I'd rather go with struct instead of enum when trying to implement the Routes (concretions). Enums cannot be extended. So you won't be allowing the creation of new requests in client side, only in the library.
I hope I've helped.
PS: Some time ago I made this repo. Maybe that could help you (specially this class). I used Combine instead of async/await, but it's not relevant to what you need.
Sometimes in Swift, it may be convenient to write an initializer for a class which delegates to JSONDecoder or a factory method. For example, one might want to write
final class Test: Codable {
let foo: Int
init(foo: Int) {
self.foo = foo
}
func jsonData() throws -> Data {
try JSONEncoder().encode(self)
}
convenience init(fromJSON data: Data) throws {
self = try JSONDecoder().decode(Self.self, from: data)
}
}
let test = Test(foo: 42)
let data = try test.jsonData()
let decodedTest = try Test(fromJSON: data)
print(decodedTest.foo)
but this fails to compile with
Cannot assign to value: 'self' is immutable.
What is the solution to work around this problem?
First, note that this limitation exists only for classes, so the example initializer will work for as-is for structs and enums, but not all situations allow changing a class to one of these types.
This limitation on class initializers is a frequent pain-point that shows up often on this site (for example). There is a thread on the Swift forums discussing this issue, and work has started to add the necessary language features to make the example code above compile, but this is not complete as of Swift 5.4.
From the thread:
Swift's own standard library and Foundation overlay hack around this missing functionality by making classes conform to dummy protocols and using protocol extension initializers where necessary to implement this functionality.
Using this idea to fix the example code yields
final class Test: Codable {
let foo: Int
init(foo: Int) {
self.foo = foo
}
func jsonData() throws -> Data {
try JSONEncoder().encode(self)
}
}
protocol TestProtocol: Decodable {}
extension Test: TestProtocol {}
extension TestProtocol {
init(fromJSON data: Data) throws {
self = try JSONDecoder().decode(Self.self, from: data)
}
}
let test = Test(foo: 42)
let data = try test.jsonData()
let decodedTest = try Test(fromJSON: data)
print(decodedTest.foo)
which works fine. If Test is the only type conforming to TestProtocol, then only Test will get this initializer.
An alternative is to simply extend Decodable or another protocol to which your class conforms, but this may be undesirable if you do not want other types conforming to that protocol to also get your initializer.
I am trying to save a configuration data structure with UserDefaults, thus the data structure needs to conform to the Codable protocol. This is my data structure:
// Data structure which saves two objects, which conform to the Connection protocol
struct Configuration {
var from: Connection
var to: Connection
}
protocol Connection: Codable {
var path: String { get set }
}
// Two implementations of the Connection protocol
struct SFTPConnection: Connection, Codable {
var path: String
var user: String
var sshKey: String
}
struct FTPConnection: Connection, Codable {
var path: String
var user: String
var password: String
}
If I just add Codable to Configuration, it won't work. So I have to implement it myself.
extension Configuration: Codable {
enum CodingKeys: String, CodingKey {
case from, to
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
let from = try container.decode(Connection.self, forKey: .from)
let to = try container.decode(Connection.self, forKey: .to)
self.from = from
self.to = to
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(from, forKey: .from)
try container.encode(to, forKey: .to)
}
}
For every call on decode() or encode() I get the error Protocol type 'Connection' cannot conform to 'Decodable/Encodable' because only concrete types can conform to protocols.
I can see that it is difficult for the compiler to identify, which class should be used to decode the given object. But I figured it should be easy to encode an object, since every object of type Connection implements the encode() method.
I know, that the problem lies with the protocol and that the protocol can't be used with Decodable/Encodable. How would I change the code in decode/encode, so that I can still use the protocol with the various implementations? My guess is to somehow tell decode/encode which implementation of the protocol to use. I would appreciate any elegant solutions for this problem!
It's a limitation of Swift that a protocol cannot conform to itself. Thus from and to do not conform to Codable as bizarre as that seems.
You can get around it by using generics which basically means you declare from and to as arbitrary types that conform to Codable. Here's how:
struct Configuration<F: Connection, T: Connection>: Codable {
var from: F
var to: T
}
let myFrom = SFTPConnection(path: "foo", user: "me", sshKey: "hgfnjsfdjs")
let myTo = FTPConnection(path: "foo", user: "me", password: "hgfnjsfdjs")
let example = Configuration(from: myFrom, to: myTo)
So F and T are types that conform to Connection. When you instantiate example in the last line, the compiler infers F is SFTPConnection and T is FTPConnection.
Once I added the generic parameters, Configuration was able to synthesise the conformance to Codable without the extension.
To answer Sh_kahn's point about having two generic parameters, I did this to allow from and to to be connections of different types. If you always want the two connections to be of the same type i.e. always two SFTPConnections or two FTPConnections you should declare the Configuration like this:
struct Configuration<C: Connection>: Codable {
var from: C
var to: C
}
Using Vapor for return model to node :
func indexView(request: Request) throws -> ResponseRepresentable
{
let acro = try Acronym.makeQuery().sort(Acronym.idKey, .ascending)
return try acro.all().makeNode(in: <#T##Context?#>)
}
It always return error and don't know how to fixed it.
Contexts are used generally to pass current-use information around inside Vapor. The Vapor 3 documentation does not appear to contain detailed information (yet), but see https://docs.vapor.codes/2.0/node/getting-started/ for Vapor 2. I have never found a need for them in makeNode, so putting:
return try acro.all().makeNode(in:nil)
should make it work.
Node has been phased out in Vapor3. There's no need for it since it relies in Swift's native data types+protocols. In this case, Vapor 3 uses Content to work with JSON. (Content conforms to Codable by default)
e.g.
final class Person: Content, MySQLModel, Migration {
var id: Int?
var name: String
init(id: Int? = nil, name: String) {
self.id = id
self.name = name
}
}
func person(_ req: Request) throws -> Future<Person> {
return Person(name: "Mark")
}
router.get("test") { req -> Future<[Person]> in
return try Person.query(on: req).sort(\.id, .ascending).all()
}
Excerpt from the docs:
In Vapor 3, all content types (JSON, protobuf, URLEncodedForm, Multipart, etc) are treated the same. All you need to parse and serialize content is a Codable class or struct.
I'm struggling to understand class/reference type behavior and how this relates to changes as I try to upgrade and reduce code using Codable in Swift 4.
I have two classes – a SuperClass with all of the data that will be persistent and that I save to UserDefaults (a place name & string with coordinates), and a SubClass that contains additional, temporary info that I don't need (weather data for the SuperClass coordinates).
In Swift 3 I used to save data like this:
func saveUserDefaults() {
var superClassArray = [SuperClass]()
// subClassArray is of type [SubClass] and contains more data per element.
superClassArray = subClassArray
let superClassData = NSKeyedArchiver.archivedData(withRootObject: superClassArray)
UserDefaults.standard.set(superClassData, forKey: " superClassData")
}
SuperClass conformed to NSObject & NSCoding
It also included the required init decoder & the encode function.
It all worked fine.
In trying to switch to Swift 4 & codable I've modified SuperClass to conform to Codable.
SuperClass now only has one basic initializer and none of the encoder/decoder stuff from Swift 3. There is no KeyedArchiving happening with this new approach (below). SubClass remains unchanged. Unfortunately I crash on the line where I try? encoder.encode [giving a Thread 1: EXC_BAD_ACCESS (code=1, address=0x10)]. My assumption is that the encoder is getting confused with identical reference types where one is SuperClass and one SubClass (subClassArray[0] === superClassArray[0] is true).
I thought this might work:
func saveUserDefaults() {
var superClassArray = [SuperClass]()
superClassArray = subClassArray
// assumption was that the subclass would only contain parts of the superclass & wouldn't produce an error when being encoded
let encoder = JSONEncoder()
if let encoded = try? encoder.encode(superClassArray){
UserDefaults.standard.set(encoded, forKey: " superClassArray ")
} else {
print("Save didn't work!")
}
}
Then, instead of creating an empty superClassArray, then using:
superClassArray = subClassArray, as shown above, I replace this with the single line:
let superClassArray: [SuperClass] = subClassArray.map{SuperClass(name: $0.name, coordinates: $0.coordinates)}
This works. Again, assumption is because I'm passing in the values inside of the class reference type & haven't made the superClassArray = subClassArray. Also, as expected, subClassArray[0] === superClassArray[0] is false
So why did the "old stuff" in Swift 3 work, even though I used the line superClassArray = subClassArray before the let superClassData = NSKeyedArchiver.archivedData(withRootObject: superClassArray)
? Am I essentially achieving the same result by creating the array in Swift 4 that was happening with the old Swift 3 encoder/decoder? Is the looping / recreation
Thanks!
Polymorphic persistence appears to be broken by design.
The bug report SR-5331 quotes the response they got on their Radar.
Unlike the existing NSCoding API (NSKeyedArchiver), the new Swift 4 Codable implementations do not write out type information about encoded types into generated archives, for both flexibility and security. As such, at decode time, the API can only use the concrete type your provide in order to decode the values (in your case, the superclass type).
This is by design — if you need the dynamism required to do this, we recommend that you adopt NSSecureCoding and use NSKeyedArchiver/NSKeyedUnarchiver
I am unimpressed, having thought from all the glowing articles that Codable was the answer to some of my prayers. A parallel set of Codable structs that act as object factories is one workaround I'm considering, to preserve type information.
Update I have written a sample using a single struct that manages recreating polymorphic classes. Available on GitHub.
I was not able to get it to work easily with subclassing. However, classes that conform to a base protocol can apply Codable for default encoding. The repo contains both keyed and unkeyed approaches. The simpler is unkeyed, copied below
// Demo of a polymorphic hierarchy of different classes implementing a protocol
// and still being Codable
// This variant uses unkeyed containers so less data is pushed into the encoded form.
import Foundation
protocol BaseBeast {
func move() -> String
func type() -> Int
var name: String { get }
}
class DumbBeast : BaseBeast, Codable {
static let polyType = 0
func type() -> Int { return DumbBeast.polyType }
var name:String
init(name:String) { self.name = name }
func move() -> String { return "\(name) Sits there looking stupid" }
}
class Flyer : BaseBeast, Codable {
static let polyType = 1
func type() -> Int { return Flyer.polyType }
var name:String
let maxAltitude:Int
init(name:String, maxAltitude:Int) {
self.maxAltitude = maxAltitude
self.name = name
}
func move() -> String { return "\(name) Flies up to \(maxAltitude)"}
}
class Walker : BaseBeast, Codable {
static let polyType = 2
func type() -> Int { return Walker.polyType }
var name:String
let numLegs: Int
let hasTail: Bool
init(name:String, legs:Int=4, hasTail:Bool=true) {
self.numLegs = legs
self.hasTail = hasTail
self.name = name
}
func move() -> String {
if numLegs == 0 {
return "\(name) Wriggles on its belly"
}
let maybeWaggle = hasTail ? "wagging its tail" : ""
return "\(name) Runs on \(numLegs) legs \(maybeWaggle)"
}
}
// Uses an explicit index we decode first, to select factory function used to decode polymorphic type
// This is in contrast to the current "traditional" method where decoding is attempted and fails for each type
// This pattern of "leading type code" can be used in more general encoding situations, not just with Codable
//: **WARNING** there is one vulnerable practice here - we rely on the BaseBeast types having a typeCode which
//: is a valid index into the arrays `encoders` and `factories`
struct CodableRef : Codable {
let refTo:BaseBeast //In C++ would use an operator to transparently cast CodableRef to BaseBeast
typealias EncContainer = UnkeyedEncodingContainer
typealias DecContainer = UnkeyedDecodingContainer
typealias BeastEnc = (inout EncContainer, BaseBeast) throws -> ()
typealias BeastDec = (inout DecContainer) throws -> BaseBeast
static var encoders:[BeastEnc] = [
{(e, b) in try e.encode(b as! DumbBeast)},
{(e, b) in try e.encode(b as! Flyer)},
{(e, b) in try e.encode(b as! Walker)}
]
static var factories:[BeastDec] = [
{(d) in try d.decode(DumbBeast.self)},
{(d) in try d.decode(Flyer.self)},
{(d) in try d.decode(Walker.self)}
]
init(refTo:BaseBeast) {
self.refTo = refTo
}
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
let typeCode = try container.decode(Int.self)
self.refTo = try CodableRef.factories[typeCode](&container)
}
func encode(to encoder: Encoder) throws {
var container = encoder.unkeyedContainer()
let typeCode = self.refTo.type()
try container.encode(typeCode)
try CodableRef.encoders[typeCode](&container, refTo)
}
}
struct Zoo : Codable {
var creatures = [CodableRef]()
init(creatures:[BaseBeast]) {
self.creatures = creatures.map {CodableRef(refTo:$0)}
}
func dump() {
creatures.forEach { print($0.refTo.move()) }
}
}
//: ---- Demo of encoding and decoding working ----
let startZoo = Zoo(creatures: [
DumbBeast(name:"Rock"),
Flyer(name:"Kookaburra", maxAltitude:5000),
Walker(name:"Snake", legs:0),
Walker(name:"Doggie", legs:4),
Walker(name:"Geek", legs:2, hasTail:false)
])
startZoo.dump()
print("---------\ntesting JSON\n")
let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
let encData = try encoder.encode(startZoo)
print(String(data:encData, encoding:.utf8)!)
let decodedZoo = try JSONDecoder().decode(Zoo.self, from: encData)
print ("\n------------\nAfter decoding")
decodedZoo.dump()
Update 2020-04 experience
This approach continues to be more flexible and superior to using Codable, at the cost of a bit more programmer time. It is used very heavily in the Touchgram app which provides rich, interactive documents inside iMessage.
There, I need to encode multiple polymorphic hierarchies, including different Sensors and Actions. By storing signatures of decoders, it not only provides with subclassing but also allows me to keep older decoders in the code base so old messages are still compatible.