2nd/10_Wiki/Topics/Coding/iOS_Combine_Patterns.md

id, title, category, status, source_trust_level, verification_status, created_at, updated_at, tags, tech_stack, applied_in, aliases

id	title	category	status	source_trust_level	verification_status	created_at	updated_at	tags	tech_stack	applied_in	aliases
ios-combine-patterns	Combine — 비동기 stream / 변환 / cancel	Coding	draft	B	conceptual	2026-05-09	2026-05-09	ios combine swift async vibe-coding	language applicable_to Swift / Combine iOS 13+		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)

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

Publishers.CombineLatest3($email, $password, $agreedToTerms)
    .map { e, p, a in e.contains("@") && p.count >= 8 && a }
    .assign(to: &$canSubmit)

Cancel

let task = publisher.sink(receiveValue: { ... })
// 화면 disappear
task.cancel()
// 또는 bag.removeAll()

async/await 와 통합

let value = try await publisher.values.first { _ in true }!

// Or convert async to publisher
extension Publisher {
    func toAsync() async throws -> Output { ... }
}

NotificationCenter — Combine

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