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The Ultimate Showdown: Combine vs. Closures in Swift

Landscape of a developer’s workspace with a screen displaying code. Above the laptop, two floating icons are prominently labeled ‘Combine’ and ‘Closures’.
Credits: Dall-E

In the ever-evolving world of Swift, we developers are constantly bombarded with choices. With the introduction of Combine in recent years and the long-standing use of Closures, the debate has become heated, also in my current assignment ….: Which approach should we adopt for handling asynchronous operations? Having had my hands deep in both tools, I felt it was time for a comprehensive breakdown.

In my current assignment, we’ve leaned heavily into closures, employing them extensively to manage our asynchronous tasks. Their prevalence in our project got me pondering: When is it apt to use closures over Combine, or vice versa?

Join me as I try to venture into the realms of Combine and Closures, dissecting their nuances and guiding you to make an informed decision for your next project.

Combine: The Swift Way of Reactive Programming

When Combine made its debut1, it was clear that Apple was taking a serious shot at functional reactive programming, trying to catch up with RXSwift . The core elements of Combine are:

  • Publishers: The rockstars that emit values over time.
  • Subscribers: The eager audience waiting for those emitted values.
  • Operators: The maestros orchestrating the transformation of values.

With Combine, you’re embracing a declarative approach. No more messy callback code using delegates; just clean, chainable operations. For instance, to fetch data and subsequently update the UI, you might employ Combine in this fashion:

import Combine

let dataPublisher = SomeAPI.fetchData()
    .receive(on: DispatchQueue.main)

var cancellable: AnyCancellable?

cancellable = dataPublisher
    .sink(receiveCompletion: { completion in
        print("Data fetch status: \(completion)")
    }, receiveValue: { data in
        refreshUI(with: data)

Closures: Swift’s Trusty Old Companions

Closures, the self-contained chunks of logic, have been with us since the dawn of Swift. They capture and store references, making them incredibly versatile:

let fetchDataClosure = { (completion: @escaping (Data?, Error?) -> Void) in
    SomeAPI.fetchData { data, error in
        completion(data, error)

fetchDataClosure { data, error in
    guard let data = data else {
        print("Error: \(error)")
    refreshUI(with: data)

Combine vs. Closures: Drawing the Battle Lines

While both tools serve asynchronous needs, they each have their distinct flair:

  • Functionality: Combine is your weapon for functional reactive programming. Closures? They’re all about encapsulating functionality.
  • Complexity: While closures are relatively straightforward, Combine, with its vast array of operators, might require a steeper learning curve.
  • Code Aesthetics: Combine offer a declarative, chainable style. Closures, on the other hand, offer a more imperative approach.
  • Application: For async operations, especially when multiple data streams are in play, Combine is your go-to. For more direct, single-shot asynchronous tasks, closures might be the better pick.

When to Choose Which?

Use for Combine when:

  • You’re navigating a sea of asynchronous events.
  • You’re a fan of the declarative style.

Lean on closures when:

  • Your asynchronous tasks are straightforward.
  • You like simplicity in your coding patterns.

Ultimately, the choice boils down to your project’s needs and your personal coding preferences. Both Combine and closures have their merits, and understanding when to leverage each will elevate the quality of your code.

In conclusion, Swift offers a rich toolkit for asynchronous programming. Whether you’re on Team Combine or Team Closure, you’re equipped to craft efficient, elegant, and powerful applications.

Happy coding, folks!

  1. Combine was introduced as a new framework by Apple at WWDC-2019 ↩︎