axiom-combine-patterns

Combine Patterns

Overview

Combine remains embedded in massive production codebases — UIKit delegates, NotificationCenter bridging, KVO observation, and @Published properties are everywhere. New code prefers async/await, but interop and maintenance of existing Combine pipelines is daily work. This skill covers the decisions and pitfalls that matter: when to use Combine vs async/await, how to avoid memory leaks, and how to bridge between the two paradigms.

Core principle: Combine is not dead — it's mature. The question isn't "should I use Combine?" but "is Combine the right tool for THIS specific data flow?"

When to Use This Skill

• Working with existing Combine pipelines
• Deciding between Combine and async/await for a new data flow
• Debugging AnyCancellable memory leaks or silent pipeline failures
• Using @Published or ObservableObject
• Bridging Combine publishers with async/await code
• Working with Subjects (PassthroughSubject, CurrentValueSubject)

When NOT to Use This Skill

• Timer.publish patterns → route via axiom-ios-concurrency to timer-patterns skill (dedicated timer lifecycle coverage)
• @Observable migration from ObservableObject → use axiom-swift-concurrency (modern observation)
• UIKit ↔ SwiftUI bridging → route via axiom-ios-ui (view wrapping, not data flow)
• General async/await patterns → use axiom-swift-concurrency

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 combineLatest and zip?"
• "How do I debounce a text field with Combine?"
• "My @Published property update isn't reaching the view"
• "How do I bridge a Combine publisher into async/await code?"

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Part 1: Combine vs async/await Decision Tree

Use Case	Combine	async/await	Why
One-shot network call	No	Yes	async/await is simpler, no cancellable management
Stream of values over time	Yes	AsyncStream	Combine's operators (debounce, combineLatest) are richer
Debounce/throttle user input	Yes	Awkward	Combine has built-in debounce/throttle; AsyncStream requires manual implementation
Merge multiple sources	Yes	TaskGroup	Combine's merge/combineLatest handle heterogeneous streams naturally
Existing UIKit KVO/Notification	Yes	Bridge	publisher(for:) and NotificationCenter.default.publisher are idiomatic Combine
New project iOS 17+	No	Yes	@Observable + async/await is the modern pattern
Existing codebase with Combine	Maintain	Migrate incrementally	Don't rewrite working pipelines — bridge at boundaries