Embracing Tradition: Swift's Asynchronous Evolution

In the realm of software development, we often encounter situations where adherence to a specific programming paradigm is not merely a choice but a necessity. Whether driven by project requirements, legacy system constraints, or organizational preferences, developers frequently find themselves compelled to adopt particular approaches, even if they initially seem restrictive. However, such constraints can sometimes lead to unexpected benefits, offering opportunities to deepen our understanding of fundamental concepts.

My recent journey through Swift's concurrency approach took us through the comparison of Combine and async/await in a previous exploration. Today, I delve into the... bedrock of Swift's asynchronous programming: Completion blocks, comparing them with the more modern paradigms.

But first ...Understanding Completion Blocks

Before the Combine and async/await was just a distant idea, there were completion blocks. These allowed developers to execute code after a task was completed, passing results through parameters in a closure. Consider a simple network request:

func fetchData(from url: URL, completion: @escaping (Data?, Error?) -> Void) {
    let task = URLSession.shared.dataTask(with: url) { data, response, error in
        completion(data, error)
    }
    task.resume()
}        

BUT.....Limitations of Completion Blocks

While completion blocks served us well, they weren't without their drawbacks. Callback hell, became a common sight in complex asynchronous flows. Managing multiple nested callbacks could quickly turn your code into an unreadable mess.

..Then...Transition to Modern Concurrency: Combine and Async/Await

As Swift evolved, so did its approach to handling asynchronous tasks. Combine and async/await were introduced as elegant solutions to the limitations of completion blocks, offering a declarative and imperative approach, respectively. These modern paradigms provide Swift developers with tools to write cleaner, more maintainable asynchronous code.

A basic Comparative Analysis

When we place completion blocks side by side with Combine and async/await, several differences emerge:

- Syntax and Readability: Completion blocks often lead to nested code that can be hard to follow, whereas Combine and async/await offer more linear and expressive syntax.

- Error Handling: Combine and async/await introduce structured error handling, allowing developers to manage errors more effectively compared to the manual checks required with completion blocks.

- Use Cases: While completion blocks are still useful for simple tasks or when working within APIs that require them, Combine and async/await shine in handling more complex asynchronous operations and streams of data.

Some Practical Examples...

Let's refactor our earlier fetchData function first using async/await:

func fetchAipopsData() async throws -> Data {
    let url = URL(string: "https://api.example.com/data")!
    let (data, _) = try await URLSession.shared.data(from: url)
    return data
}        

And now with Combine:

import Combine

func fetchAipopsDataPublisher() -> AnyPublisher<Data, URLError> {
    let url = URL(string: "https://api.example.com/data")!
    return URLSession.shared.dataTaskPublisher(for: url)
        .map(\.data)
        .eraseToAnyPublisher()
}        

Both examples (even if I venture into pseudo-territory and use a bit of forced unpacking, the core message should remain crystal clear to the reader) demonstrate how this modern concurrency approach can offer more streamlined approaches compared to the traditional completion block method.

But But.....

But, now imagine that your project contract specifically asks you to hold on to that trusty hammer. It may not have the latest tool era, but it has a proven track record for getting shit done.

Often a developer is in a position where we are told to follow a certain paradigm, and here it's not just about following rules - but it's also an opportunity to showcase the versatility and ongoing effectiveness of old but proven tools, eg completion blocks.

So while we can try to navigate Swift's array of asynchronous programming options with our "hammer" in hand, we're reminded that sometimes the traditional tools are exactly what we need to build something robust and reliable.

// Thomas