Callbacks Vs Completion Handlers in Swift: What’s the Difference? 🚀

As I dive deeper into Swift and modern concurrency, I realized how crucial understanding callbacks and completion handlers is for writing robust and clean code. While both seem similar, here’s a quick differentiation:

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What are Callbacks?

Callbacks are functions passed as arguments to another function and executed later. They’re versatile and can be used for both synchronous and asynchronous tasks.

🔹 Example:

func calculate(a: Int, b: Int, callback: (Int) -> Void) {
    let result = a + b
    callback(result)
}

calculate(a: 3, b: 5) { sum in
    print("Sum: \(sum)")  // Sum: 8
}

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What about Completion Handlers?

Completion handlers are a specific type of callback used in asynchronous tasks to signal the end of an operation, often returning a result or an error.

🔹 Example:

func fetchData(completion: @escaping (String) -> Void) {
    DispatchQueue.global().async {
        sleep(2)
        DispatchQueue.main.async {
            completion("Data fetched")
        }
    }
}

fetchData { result in
    print(result)  // Data fetched
}

Key Differences Between Callbacks and Completion Handlers:

This understanding bridges the gap between writing basic Swift code and creating scalable, high-performance apps. 💻

💡 Pro Tip: Whether using callbacks or completion handlers, ensure you handle errors and always execute UI updates on the main thread!