combine-code-review

Combine Code Review

Quick Reference

Review Checklist

• All sink closures use [weak self] when self owns cancellable
• No assign(to:on:self) usage (use assign(to: &$property) or sink)
• All AnyCancellables stored in Set or property (not discarded)
• Subjects exposed as AnyPublisher via eraseToAnyPublisher()
• flatMap used correctly (not when map + switchToLatest needed)
• Error handling inside flatMap to keep main chain alive
• tryMap followed by mapError to restore error types
• receive(on: DispatchQueue.main) before UI updates
• PassthroughSubject for events, CurrentValueSubject for state
• Future wrapped in Deferred when used with retry

When to Load References

• Reviewing Subjects or publisher selection → publishers.md
• Reviewing operator chains or combining publishers → operators.md
• Reviewing subscriptions or memory issues → memory.md
• Reviewing error handling or try* operators → error-handling.md

Hard gates (before you report findings)

Complete in order. Do not skip ahead while a prior gate is open.

1. Scope — Pass: You name at least one file or type under review that imports Combine or uses APIs from the Quick Reference (e.g. AnyPublisher, @Published, PassthroughSubject). If none apply, stop with “out of scope.”
2. Subscription retention — Pass: For each sink, assign, and store(in:) in scope, you state where the AnyCancellable is retained (property, Set, task lifetime) or mark ephemeral with a one-line reason (e.g. synchronous one-shot that cannot outlive caller). If you cannot tell from the snippet, say unknown and ask for surrounding storage, do not assume safe.
3. Retain-cycle claim — Pass: Confirmed leak findings state the capture chain (e.g. self → stored cancellable → closure strongly capturing self). Label suspected cases risk / verify, not confirmed leaks. When arguing safety, cite [weak self], [unowned self], or non-capturing patterns you relied on.
4. UI / main thread — Pass: For updates to UIKit/SwiftUI from a chain, you either point to receive(on: DispatchQueue.main), @MainActor, or equivalent before the UI work, or flag missing scheduling with file:line.
5. Severity and checklist — Pass: Every high or critical item includes file:line (or exact pasted lines) and names which Review Checklist row it breaks. Lower-severity notes may omit line numbers but must still be reproducible from named files.