Combine Patterns

Combine reactive programming patterns for production iOS codebases — decision-making, pitfall prevention, and async/await bridging.

When to Use

Use this skill when:

• Deciding between Combine and async/await for a data flow
• Debugging silent pipeline failures or AnyCancellable leaks
• Working with @Published properties or ObservableObject
• Bridging Combine publishers with async/await code
• Using Subjects, operators, or reactive patterns

Example Prompts

• "Should I use Combine or async/await for this?"
• "My Combine pipeline silently stops producing values"
• "How do I convert a publisher to an async sequence?"
• "AnyCancellable is leaking — where do I store it?"
• "What's the difference between debounce and throttle?"
• "How do I bridge a Combine publisher into async/await code?"
• "My @Published property update isn't reaching the view"

What This Skill Provides

• Combine vs async/await decision tree — When each is the right tool, with specific use cases
• AnyCancellable lifecycle rules — Why Set not Array, 4 memory leak patterns with fixes (including assign(to🔛) retain cycle)
• Essential operators — One canonical example per group (transform, combine, time, error)
• @Published traps — willSet timing, nested ObservableObject, thread safety
• Bridging patterns — .values for Publisher → AsyncSequence, Future for async → Publisher
• Subject patterns — PassthroughSubject vs CurrentValueSubject, send-after-completion pitfall
• Cold vs hot publishers — share()/multicast() gotchas, when to use each
• Silent pipeline diagnosis — Checklist for when pipelines stop producing values

Related

• Swift Concurrency — Modern async/await patterns; use for new code on iOS 17+
• Timer Patterns (routed via axiom-ios-concurrency) — Dedicated Timer/DispatchSourceTimer lifecycle; use for Timer.publish patterns
• Memory Debugging (routed via axiom-ios-performance) — Instruments-based leak diagnosis when Combine pipelines cause retain cycles