[G1-Sync] Manual knowledge update

10_Wiki/Topics/Coding/iOS_Combine_Patterns.md

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+---
+id: ios-combine-patterns
+title: Combine — 비동기 stream / 변환 / cancel
+category: Coding
+status: draft
+source_trust_level: B
+verification_status: conceptual
+created_at: 2026-05-09
+updated_at: 2026-05-09
+tags: [ios, combine, swift, async, vibe-coding]
+tech_stack: { language: "Swift / Combine", applicable_to: ["iOS 13+"] }
+applied_in: []
+aliases: [Publisher, Subscriber, AnyCancellable, sink]
+---
+
+# Combine — 비동기 stream
+
+> Apple 의 reactive framework. async/await 가 더 단순하지만, Combine 은 **변환 체인 / 동시 source 결합 / 자동 cancel** 에서 강함. SwiftUI 와 자연스럽게 통합.
+
+## 📖 핵심 개념
+- Publisher: 값 stream emit.
+- Subscriber: 값 받기.
+- Operator: map / filter / debounce / combineLatest / merge.
+- AnyCancellable: subscription handle. dispose 시 자동 cancel.
+
+## 💻 코드 패턴
+
+### Search debounce (typical)
+```swift
+import Combine
+
+final class SearchViewModel: ObservableObject {
+    @Published var query: String = ""
+    @Published var results: [Item] = []
+    private var bag = Set<AnyCancellable>()
+
+    init() {
+        $query
+            .debounce(for: .milliseconds(300), scheduler: DispatchQueue.main)
+            .removeDuplicates()
+            .filter { $0.count >= 2 }
+            .map { q in
+                URLSession.shared.dataTaskPublisher(for: searchURL(q))
+                    .map(\.data)
+                    .decode(type: [Item].self, decoder: JSONDecoder())
+                    .replaceError(with: [])
+            }
+            .switchToLatest() // 이전 검색 cancel
+            .receive(on: DispatchQueue.main)
+            .assign(to: &$results)
+    }
+}
+```
+
+### combineLatest
+```swift
+Publishers.CombineLatest3($email, $password, $agreedToTerms)
+    .map { e, p, a in e.contains("@") && p.count >= 8 && a }
+    .assign(to: &$canSubmit)
+```
+
+### Cancel
+```swift
+let task = publisher.sink(receiveValue: { ... })
+// 화면 disappear
+task.cancel()
+// 또는 bag.removeAll()
+```
+
+### async/await 와 통합
+```swift
+let value = try await publisher.values.first { _ in true }!
+
+// Or convert async to publisher
+extension Publisher {
+    func toAsync() async throws -> Output { ... }
+}
+```
+
+### NotificationCenter — Combine
+```swift
+NotificationCenter.default.publisher(for: UIApplication.didBecomeActiveNotification)
+    .sink { _ in self.refresh() }
+    .store(in: &bag)
+```
+
+## 🤔 의사결정 기준
+| 상황 | Combine | async/await |
+|---|---|---|
+| 한 번 호출 | ❌ | ✅ |
+| Stream of values (search, websocket) | ✅ | AsyncSequence |
+| 여러 source 결합 | ✅ — combineLatest | 직접 await |
+| SwiftUI @Published / assign | ✅ | manual setState |
+| iOS 13 호환성 | ✅ | iOS 15+ |
+| Time-based (debounce, throttle) | ✅ | 직접 구현 |
+
+## ❌ 안티패턴
+- **AnyCancellable 무시**: `_ = publisher.sink(...)` — 즉시 deallocate. store(in: &bag).
+- **메인 스레드에서 무거운 변환**: receive(on: DispatchQueue.global()) 으로 분기.
+- **switchToLatest 안 씀**: 검색 결과 race. 이전 결과가 새 결과 덮어씀.
+- **assign 후 weak self 안 함**: cycle. assign(to: &$x) 또는 sink + [weak self].
+- **error 처리 누락**: .sink 의 receiveCompletion 무시 → silent failure.
+- **모든 곳 Combine**: async/await 가 더 단순한 경우 많음.
+
+## 🤖 LLM 활용 힌트
+- 검색 / 스트림 / SwiftUI binding = Combine 적합.
+- 한 번 호출 = async/await.
+
+## 🔗 관련 문서
+- [[iOS_Swift_Concurrency_async_await]]
+- [[iOS_SwiftUI_State_Property_Wrappers]]