Modern iOS Architecture: Swift Concurrency and the Composable Architecture (TCA) in 2026

The Composable Architecture (TCA) has emerged as one of the most prominent architecture paradigms in the iOS ecosystem. As Swift Concurrency has matured in Swift 6, TCA has adapted, integrating first-class support for structured concurrency, actors, and compiler-enforced data isolation.

In this article, we’ll build a state-of-the-art TCA feature using modern macros, strict concurrency limits, and async-first effects.

The Modern TCA Feature Stack

With modern TCA releases, boilerplate has been dramatically reduced. Reducers are declared using macros like @Reducer and state structures are initialized with direct property observers.

Let’s look at a complete implementation of a search-as-you-type feature that integrates debounce and asynchronous network calls using Swift Concurrency:

import ComposableArchitecture
import Foundation

@Reducer
struct SearchFeature {
    @ObservableState
    struct State: Equatable {
        var query = ""
        var results: [String] = []
        var isLoading = false
    }
    
    enum Action {
        case queryChanged(String)
        case searchResponse(Result<[String], Error>)
    }
    
    @Dependency(\.searchClient) var searchClient
    
    var body: some ReducerOf<Self> {
        Reduce { state, action in
            switch action {
            case let .queryChanged(query):
                state.query = query
                guard !query.isEmpty else {
                    state.results = []
                    return .none
                }
                state.isLoading = true
                
                return .run { [query = state.query] send in
                    // Debounce using native Task.sleep
                    try await Task.sleep(for: .seconds(0.3))
                    
                    let results = try await searchClient.search(query)
                    await send(.searchResponse(.success(results)))
                } catch: { error, send in
                    await send(.searchResponse(.failure(error)))
                }
                
            case let .searchResponse(.success(results)):
                state.isLoading = false
                state.results = results
                return .none
                
            case .searchResponse(.failure):
                state.isLoading = false
                state.results = []
                return .none
            }
        }
    }
}

Actor Isolation & Dependency Injection

One of TCA’s primary strengths is its dependency system. In 2026, dependencies should isolate asynchronous work onto custom actors to maintain strict concurrency safety.

Here is the search client interface conforming to dependency requirements:

struct SearchClient: Sendable {
    var search: @Sendable (String) async throws -> [String]
}

extension SearchClient: DependencyKey {
    static let liveValue = Self(
        search: { query in
            let url = URL(string: "https://api.portfolio.dev/search?q=\(query)")!
            let (data, _) = try await URLSession.shared.data(from: url)
            return try JSONDecoder().decode([String].self, from: data)
        }
    )
}

extension DependencyValues {
    var searchClient: SearchClient {
        get { self[SearchClient.self] }
        set { self[SearchClient.self] = newValue }
    }
}

Architectural Takeaways

By combining TCA with Swift Concurrency, you build codebases that are:

1. Statically Safe: The Swift 6 compiler guarantees no concurrent read/writes to the state.
2. Highly Testable: Reducer state transitions are completely deterministic and can be verified with TestStore.
3. Decoupled: Clean separation between side-effects (networking, disk access) and presentation layers.