Swift Concurrency is more than just a feature—it’s a revolution in how we write asynchronous code. But to truly understand its impact, we need to look back at where it all began. The journey to Swift’s modern async/await system wasn’t an overnight decision. It was born out of years of experience, challenges, and a vision for a better way to handle concurrency.

The Problem: Managing Complexity in Concurrent Code

Before Swift Concurrency, handling asynchronous operations in Swift required a tangled web of completion handlers, delegation patterns, and third-party solutions like Grand Central Dispatch (GCD) or Operation Queues. While these tools were powerful, they often led to deeply nested code—commonly known as “callback hell”—which made reasoning about program flow incredibly difficult.

Moreover, writing concurrent code safely was a challenge. Data races, thread explosion, and synchronization issues were common pitfalls. Developers had to manually ensure thread safety, often leading to hard-to-debug issues and unpredictable behavior.

A Vision for a Better Future

In 2017, Chris Lattner, the original creator of Swift, proposed the Swift Concurrency Manifesto. His vision was clear: Swift needed a modern concurrency model that was easy to use, highly performant, and safe by design.

The manifesto laid out several key goals:

• Structured Concurrency – A way to model asynchronous operations hierarchically, making it easier to manage their lifecycle.
• Safer Data Access – Eliminating data races through compiler-enforced rules and actor-based isolation.
• Simplicity – Reducing boilerplate and making async code as readable as synchronous code.
• Compatibility – Ensuring smooth integration with existing Swift codebases and APIs.

Enter async/await

The async/await model, inspired by languages like JavaScript and C#, was the natural evolution for Swift. It allows developers to write asynchronous code that looks and behaves just like synchronous code, making it easier to follow and debug.

Consider the difference:

Before (Completion Handlers):

fetchData { result in
    switch result {
    case .success(let data):
        processData(data) { processedData in
            displayData(processedData)
        }
    case .failure(let error):
        handleError(error)
    }
}

After (Async/Await):

let data = try await fetchData()
let processedData = try await processData(data)
displayData(processedData)

With async/await, we eliminate callback nesting and make the flow of execution much clearer.

The Road to Today

It took years of refinement, collaboration, and iteration to bring Swift Concurrency to life. Swift 5.5 introduced async/await, task-based concurrency, and actors—ushering in a new era for Swift development. We’re now getting familiar with Swift 6 and there’s more enhancements to be expected.

By embracing these features, we can write safer, more readable, and more maintainable concurrent code. Structured concurrent code—but what does Structured Concurrency actually mean? We’ll discuss that in the next lesson.