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

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

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2 min read

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:


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.

πŸ”Ή 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
}

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.

πŸ”Ή 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
}
AspectCallbackCompletion Handler
DefinitionA general term for passing functions as arguments.A type of callback used to signal task completion.
Typical UsageSynchronous or asynchronous operations.Specifically for asynchronous tasks (e.g., APIs).
FocusFlexible; can be used for intermediate or final steps.Always indicates the end of a task.
Error HandlingError handling is optional.Often uses the Result type or optional error.
TerminologyBroader programming concept.Specific to task completion, commonly used in Swift.

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

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