The No-Nonsense Guide to Combine vs. Async/Await

In my current project, we initially adopted RxSwift in 2021 as our go-to solution for handling asynchronous tasks. However, as Combine matured and became an integral part of the Swift Concurrency paradigm, I felt it was time to make the switch. During the transition phase, one of our developers started using async/await, which left me pondering when to use one approach over the other. To gain a better understanding of Swift Concurrency, I decided to investigate the differences between Combine and async/await and their respective use cases.

In this article, I'll dive into the distinctions between Combine and async/await and provide guidance on when to choose one over the other.

Spoiler alert - it all goes down to making your asynchronous code cleaner, more efficient, and easier to manage.

Combine: Apple's response to RxSwift

Combine hit the scene in 2019, and it's all about managing async events and data streams in a neat, organized way. Here's the lowdown on the main components of Combine:

??Publishers: These guys emit values over time.

??Subscribers: They receive the values from publishers.

??Operators: They transform and mess with the values from publishers.

Combine helps you deal with async events in a declarative way, letting you chain operations together without a callback code.

Let's say you want to fetch some data and update the UI when the data is available. Using Combine, you might do something like this:

import Combine

let url = URL(string: "https://api.aipops.com/data")!
let dataPublisher = URLSession.shared.dataTaskPublisher(for: url)
? ? .map(\.data)
? ? .decode(type: AipopsData.self, decoder: JSONDecoder())
? ? .receive(on: DispatchQueue.main)
? ? .eraseToAnyPublisher()

var cancellable: AnyCancellable?

cancellable = dataPublisher
? ? .sink(receiveCompletion: { completion in
? ? ? ? print("Finished: \(completion)")
? ? }, receiveValue: { myData in
? ? ? ? updateUI(with: myData)
? ? })        

Async/Await: Making Async Code feel more like the old days

Async/await came onto the scene in Swift 5.5 and made writing async code so much easier. You just write async functions using the 'async' keyword and call them with the 'await' keyword. The result? Clean, linear code that's easy to read and maintain. While Combine is declarative, Async/Await is built around the more traditional imperative programming paradigm.

Now, let's see how to accomplish the same task using async/await:

import UIKit

func fetchAipopsData() async throws -> AipopsData.self {
? ? let url = URL(string: "https://api.aipops.com/data")!
? ? let (data, _) = try await URLSession.shared.data(from: url)
? ? let aipopsData = try JSONDecoder().decode(AipopsData.self, from: data)
? ? return aipopsData
}

func updateUIAsync() async {
? ? do {
? ? ? ? let aipopsData = try await fetchAipopsData()
? ? ? ? DispatchQueue.main.async {
? ? ? ? ? ? updateUI(with: aipopsData)
? ? ? ? }
? ? } catch {
? ? ? ? print("Error fetching data: \(error)")
? ? }
}        

Combine vs. Async/Await: What's the Difference?

Both Combine and async/await help you manage async code, but they've got some key differences:

??How They Work: Combine is all about functional reactive programming, while async/await sticks to a the imperative programming style.

??Learning Curve: Async/await is easier to pick up, while Combine takes a bit more time to learn, especially if you're new to functional reactive programming..or especially if you are new to Swift and come straight from Objective-C:-)

??Code Style: Combine's declarative code is concise and expressive, while async/await keeps things simple and linear.

??Use Cases: Combine shines when you're dealing with lots of async data streams and complex event handling. Async/await is perfect for simpler async tasks, like downloading data or running a single background operation.

Now that you know the differences between Combine and async/await, you'll be ready to tackle questions or tasks that come your way plus, you'll be able to choose the right approach for your projects, making your code more efficient and easier to maintain.

But wait, there's more! To make the habit hole a little deeper, consider exploring these additional topics:

??Task Groups: In Swift Concurrency, task groups allow you to run multiple async tasks concurrently and wait for their completion.

??Custom Executors: Executors handle the scheduling and running of tasks in Swift Concurrency. Learning about custom executors can help you optimize your code to run on specific hardware or system resources, giving you greater control over performance.

??Error Handling: Both Combine and async/await have ways to handle errors that arise during asynchronous operations. Understanding how to handle errors effectively in both approaches will demonstrate your ability to write robust, fault-tolerant code.

When should one be used over the other?

Go for Combine when:

• You've got lots of async stuff and events to handle.
• You like the declarative coding way.

Pick async/await when:

• You're handling simple async tasks, like fetching data.
• You like to keep coding simple and straightforward.

Just choose what feels right for your project and coding style, and you'll be all set with efficient and easy-to-read code.

So there you have it, folks! You're now armed with the knowledge to make an informed decision about when to use Combine and async/await in your projects...Happy coding!