Swift Combine

This skill covers Apple’s Combine framework for reactive programming and handling asynchronous events.

Overview

Combine is a declarative Swift API for processing values over time. It provides a unified approach to handling asynchronous events, user interface updates, and data streams.

Available References

• Publishers & Subscribers – Core concepts and lifecycle
• Operators – Transforming, filtering, and combining streams
• Integration – Using Combine with UIKit, SwiftUI, and Foundation

Quick Reference

Basic Publisher

import Combine

// Published property
@Published var username: String = ""

// CurrentValueSubject
let subject = CurrentValueSubject<String, Never>("initial")

// PassthroughSubject
let passthrough = PassthroughSubject<Int, Never>()

// Just publisher
let just = Just("value")

// Future publisher
let future = Future<String, Error> { promise in
    promise(.success("result"))
}

Subscribing

// Sink
let cancellable = publisher.sink(
    receiveCompletion: { completion in
        switch completion {
        case .finished:
            print("Completed")
        case .failure(let error):
            print("Error: \(error)")
        }
    },
    receiveValue: { value in
        print("Value: \(value)")
    }
)

// Assign
let cancellable = publisher
    .assign(to: \.text, on: label)

Storing Subscriptions

private var cancellables = Set<AnyCancellable>()

publisher
    .sink { value in
        print(value)
    }
    .store(in: &cancellables)

Common Operators

publisher
    .filter { $0 > 0 }
    .map { $0 * 2 }
    .debounce(for: .seconds(0.5), scheduler: RunLoop.main)
    .removeDuplicates()
    .sink { value in
        print(value)
    }

Combine vs Async/Await

Best Practices

1. Store cancellables – Prevent memory leaks
2. Use weak self – Avoid retain cycles
3. Handle errors – Always handle completion
4. Thread safety – Use receive(on:) for UI
5. Cancel properly – Clean up subscriptions
6. Avoid overuse – Combine is powerful but not for everything
7. Test pipelines – Use expectations for async

For More Information

Visit https://swiftzilla.dev for comprehensive Combine documentation.