Task cancellation.swift

cancellation.swift

// original code, intermediate variable
class SomeViewModel1: ObservableObject {
    @Published var searchResults: [String] = []
    private var currentSearchTask: Task<Void, Never>?
    @MainActor
    func search(_ query: String) {
        currentSearchTask?.cancel()
        let newTask = Task {
            do {
                try await Task.sleep(for: .milliseconds(500))
                print("Starting to search!")
                searchResults = Self.articleTitlesDatabase
                    .filter { $0.lowercased().contains(query.lowercased()) }
            } catch {
                print("Search was cancelled!")
            }
        }
        currentSearchTask = newTask
    }
    static var articleTitlesDatabase: [String] {
        []
    }
}

// revised code, direct assignment
class SomeViewModel2: ObservableObject {
    @Published var searchResults: [String] = []
    private var currentSearchTask: Task<Void, Never>?
    @MainActor
    func search(_ query: String) {
        currentSearchTask?.cancel()
        currentSearchTask = Task {
            do {
                try await Task.sleep(for: .milliseconds(500))
                print("Starting to search!")
                searchResults = Self.articleTitlesDatabase
                    .filter { $0.lowercased().contains(query.lowercased()) }
            } catch {
                print("Search was cancelled!")
            }
        }
    }
    static var articleTitlesDatabase: [String] {
        []
    }
}

// preferred code, called from .task(id: text) { await viewModel.search(text) }
class SomeViewModel3: ObservableObject {
    @Published var searchResults: [String] = []
    @MainActor
    func search(_ query: String) async {
        do {
            try await Task.sleep(for: .milliseconds(500))
            print("Starting to search!")
            searchResults = Self.articleTitlesDatabase
                .filter { $0.lowercased().contains(query.lowercased()) }
        } catch {
            print("Search was cancelled!")
        }
    }
    static var articleTitlesDatabase: [String] {
        []
    }
}