The last word Mix framework tutorial in Swift

Get began with the model new declarative Mix framework in apply utilizing Swift. I am going to educate you all of the goodies from zero to hero.


What’s Mix?

Customise dealing with of asynchronous occasions by combining event-processing operators. – Apple’s Mix Framework

In different phrases, it means that you can write practical reactive code in a declarative method utilizing Swift. Purposeful reactive programming (FRP) is a particular paradigm used to cope with asynchronous code. It is a particular sort of practical programming, the place you might be working with async streams of values. So mainly you possibly can course of and rework values over time utilizing practical strategies like map, flatMap, and so forth. Mix is the “native” Swift implementation of this programming paradigm, made by Apple.

Publishers, Operators, Subscribers

I already made a quick networking instance of utilizing Mix, which is sweet if you happen to’re simply in search of a easy code snippet to simplify your URLSession requests. Enable me to seize one instance and paste it right here once more, I am going to present you why… 🤔

personal var cancellable: AnyCancellable?

self.cancellable = URLSession.shared.dataTaskPublisher(for: url)
.map { $0.information }
.decode(kind: [Post].self, decoder: JSONDecoder())
.replaceError(with: [])
.sink(receiveValue: { posts in


An important factor right here is the brand new dataTaskPublisher technique. It creates Writer that may ship (aka. publish) sequences of values over time.

Shifting ahead to the subsequent few strains we are able to see examples of assorted Operator features ( map, decode, replaceError, ereaseToAnyPublisher). They’re particular practical strategies and so they all the time return a Writer. Through the use of operators you possibly can chain a bunch of publishers collectively, this offers us that good declarative syntax that I discussed earlier than. Purposeful programming is superior! 😎

The ultimate member of the Mix household is the Subscriber. Since we are able to publish all type of issues, we are able to assume that on the opposite finish of the writer chain, there shall be some type of object that is going to make use of our last consequence. Staying with our present instance, the sink technique is a built-in operate that may join a writer to a subscriber. You will study the opposite one in a while… trace: assign.

Advantages of utilizing the Mix framework

I imagine that Mix is a large leap ahead and everybody ought to study it. My solely concern is that you could solely use it in case you are concentrating on iOS13 or above, however it will fade away (in a blink) with time, similar to it was with assortment and stack views.

Do you bear in mind iOS6? Yeah, subsequent up: iOS14!!!

Anyway, there are a bunch of goodies that Mix will deliver you:

  • Simplified asynchronous code – no extra callback hells
  • Declarative syntax – simpler to learn and keep code
  • Composable elements – composition over inheritance & reusability
  • Multi-platform – besides on linux, we’re good with SwiftNIO‘s method
  • Cancellation help – it was all the time a problem with Guarantees
  • Multithreading – you do not have to fret about it (that a lot)
  • Constructed-in reminiscence administration – no extra luggage to hold on

That is the way forward for aysnc programming on Apple plaftorms, and it is brighter than it was ever earlier than. This is without doubt one of the greatest updates for the reason that utterly revamped GCD framework API in Swift. Oh, by the way in which you would possibly ask the query…

GCD vs Mix vs Rx vs Guarantees

My recommendation is to stick with your present favourite answer for about one 12 months (however solely in case you are pleased with it). Study Mix and be ready to flip the change, if the time comes, however in case you are simply beginning a brand new challenge and you may go along with iOS13+ then I counsel to go along with Mix solely. You will note how wonderful it’s to work with this framework, so I in case you are nonetheless not satisfied, it is time to…

Study Mix by instance

Since there are some nice articles & books about utilizing Mix, I made a decision to assemble solely these sensible examples and patterns right here that I exploit regularly.

Constructed-in publishers

There are only a few built-in publishers within the Basis framework, however I feel the quantity will develop quickly. These are those that I used principally to simplify my code:


You need to use Mix to get periodic time updates by way of a writer:

var cancellable: AnyCancellable?

cancellable = Timer.publish(each: 1, on: .most important, in: .default)
.sink {

let timerPublisher = Timer.publish(each: 1.0, on: RunLoop.most important, in: .default)
cancellable = timerPublisher
.sink {

let cancellableTimerPublisher = timerPublisher.join()

You can begin & cease the writer any time you want by utilizing the join technique.

Mix has built-in help for cancellation. Each the sink and the assign strategies are returning an object that you could retailer for later and you may name the cancel technique on that AnyCancellable object to cease execution.


It’s also possible to subscribe to notifications by utilizing publishers.

extension Notification.Identify {
    static let instance = Notification.Identify("instance")

class ViewController: UIViewController {

    var cancellable: AnyCancellable?

    override func viewDidLoad() {

        self.cancellable = NotificationCenter.Writer(middle: .default, identify: .instance, object: nil)
        .sink { notification in

        NotificationCenter.default.submit(identify: .instance, object: nil)

In case you save the cancellable object as a saved property you possibly can retain the subscription till you name the cancel technique. Ensure you do not make additional retain cycles, so if you happen to want self contained in the sink block, all the time use aweak or unowned reference.


I am not going to repeat myself right here once more, as a result of I already made an entire tutorial about use URLSession with the Mix framework, so please click on the hyperlink if you wish to study extra about it.

That is it about built-in publishers, let’s check out…

Revealed variables

Property Wrappers are a model new function accessible from Swift 5.1. Mix comes with one new wrapper known as @Revealed, which can be utilized to connect a Writer to a single property. In case you mark the property as @Revealed, you possibly can subscribe to worth adjustments and you may also use these variables as bindings.

import UIKit
import Mix

class ViewController: UIViewController {

    @IBOutlet weak var textLabel: UILabel!
    @IBOutlet weak var actionButton: UIButton!

    @Revealed var labelValue: String? = "Click on the button!"

    var cancellable: AnyCancellable?

    override func viewDidLoad() {

        self.cancellable = self.$labelValue.obtain(on: DispatchQueue.most important)
                                           .assign(to: .textual content, on: self.textLabel)


    @IBAction func actionButtonTouched(_ sender: UIButton) {
        self.labelValue = "Whats up World!"

Through the use of the $ signal and the assign operate we are able to create a binding and subscribe to worth adjustments, so if the labelValue property adjustments, it’s going to be assigned to the textual content property of the textLabel variable. In different phrases, the precise textual content of the label shall be up to date on the consumer interface. Additionally you solely need to get updates on the principle queue, since we’re doing UI associated stuff. You need to use the obtain operator for this.

Customized publishers

Making a customized writer will not be so exhausting that you just would possibly suppose, however truthfully I by no means needed to make one for myself but. Nonetheless there are some very nice use-cases the place constructing a customized writer is the appropriate method to go. Antoine v.d. SwiftLee has an incredible tutorial about create a customized mix writer to increase UIKit, you must positively test that out if you wish to study extra about customized publishers.


A topic can be utilized to switch values between publishers and subscribers.

let topic = PassthroughSubject<String, By no means>()

let anyCancellable = topic
.sink { worth in

topic.ship("Whats up")

let writer = Simply("world!")


enum SubjectError: LocalizedError {
    case unknown
let errorSubject = PassthroughSubject<String, Error>()
errorSubject.ship(completion: .failure(SubjectError.unknown))

You possibly can ship values or errors to the topic manually or you possibly can subscribe a writer to a topic. They’re extraordinarily helpful if you would like to make a Mix-like interface for a standard delegate sample based mostly API. Take into account the next instance as a really primary place to begin, however I hope you will get the thought. 💡

class LocationPublisher: NSObject {

    let topic = PassthroughSubject<[CLLocation], Error>()


extension LocationPublisher: CLLocationManagerDelegate {

    func locationManager(_ supervisor: CLLocationManager, didUpdateLocations places: [CLLocation]) {

    func locationManager(_ supervisor: CLLocationManager, didFailWithError error: Error) {
        self.topic.ship(completion: .failure(error))

Futures and guarantees

I have already got a tutorial for learners about guarantees in Swift, if it’s worthwhile to perceive the reasoning behind these sorts, please learn that article first.

Mix has it is personal future / promise implementation, which is surprisingly well-made. I exploit them fairly often if I’ve an async callback block, I often rework that operate right into a promisified model (returning a writer), by utilizing a future.

func asyncMethod(completion: ((String) -> Void)) {

func promisifiedAsyncMethod() -> AnyPublisher<String, By no means> {
    Future<String, By no means> { promise in
        asyncMethod { worth in


Simply is produced from a generic consequence kind and a By no means failure kind. It simply offers you a single worth, then it is going to terminate. It is fairly helpful if you wish to fallback to a default worth, otherwise you simply need to return a price.

let simply = Simply<String>("only a worth")

simply.sink(receiveCompletion: { _ in

}) { worth in


You possibly can add a delay to a writer by utilizing a scheduler, for instance if you would like so as to add a 1 second delay, you should use the next snippet:

return Future<String, Error> { promise in
.delay(for: .init(1), scheduler: RunLoop.most important)

Error dealing with

As I discussed earlier than the By no means kind is signifies no errors, however what occurs if a writer returns an precise error? Properly, you possibly can catch that error, or you possibly can rework the error kind into one thing else by utilizing the mapError operator.

.sink(receiveCompletion: { completion in
    change completion {
    case .completed:
    case .failure(let error):
}, receiveValue: { worth in

_ = Future<String, Error> { promise in
    promise(.failure(NSError(area: "", code: 0, userInfo: nil)))
.mapError { error in
    return error
.catch { error in
.sink(receiveCompletion: { _ in

}, receiveValue: { worth in

In fact that is simply the tip of the iceberg, you possibly can assert errors and plenty of extra, however I hardly use them each day. Often I deal with my errors within the sink block.


You need to use the handleEvents operator to look at emitted occasions, the opposite choice is to place breakpoints into your chain. There are a couple of helper strategies with the intention to do that, you must learn this article about debugging Mix if you wish to know extra. 👍

.handleEvents(receiveSubscription: { subscription in

}, receiveOutput: { output in

}, receiveCompletion: { completion in

}, receiveCancel: {

}, receiveRequest: { request in



.breakpoint(receiveSubscription: { subscription in
}, receiveOutput: { output in
}, receiveCompletion: { completion in


Teams and dependencies

I’ve examples for each instances in my different article about Mix & URLSession, so please go and skim that if you would like to learn to zip collectively two publishers.


Mix is a very nice framework, you must definitively study it will definitely. It is also a very good alternative to refactor your legacy / callback-based code into a pleasant fashionable declarative one. You possibly can merely rework all of your old-school delegates into publishers by utilizing topics. Futures and guarantees may help you to maneuver away from callback blocks and like publishers as a substitute. There are many good assets about Mix across the net, additionally the official documentation is actual good. 📖

Sooner or later, fulfill a promise to study Mix.

I hope you loved this submit, be happy to ship me your feedbacks on twitter.