Combine Code Review

Reviews Combine framework code for memory leaks, operator misuse, and error handling. Use when reviewing code with import Combine, AnyPublisher, @Published, PassthroughSubject, or CurrentValueSubject.

Quick Reference

Issue Type	Reference
Publishers, Subjects, AnyPublisher	references/publishers.md
map, flatMap, combineLatest, switchToLatest	references/operators.md
AnyCancellable, retain cycles, [weak self]	references/memory.md
tryMap, catch, replaceError, Never	references/error-handling.md

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.

Review Questions

1. Are all subscriptions being retained? (Check for discarded AnyCancellables)
2. Could any sink or assign create a retain cycle with self?
3. Does flatMap need to be switchToLatest for search/autocomplete?
4. What happens when this publisher fails? (Will it kill the main chain?)
5. Are error types preserved or properly mapped after try* operators?