---
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]]
