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Type-erased Swift Task that cancels itself on deinit
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| /// A type-erased task that you can store in a collection | |
| /// to allow you to cancel at a later date. | |
| /// | |
| /// Upon deinit of the task, the task will be cancelled | |
| /// automatically. Similar to Combine's AnyCancellable. | |
| final class AnyTask { | |
| /// Call this cancellation block to cancel the task manually. | |
| let cancel: () -> Void | |
| /// Checks whether the task is cancelled. | |
| var isCancelled: Bool { isCancelledBlock() } | |
| private let isCancelledBlock: () -> Bool | |
| deinit { | |
| // On deinit, if the task is not cancelled then cancel it | |
| if !isCancelled { cancel() } | |
| } | |
| /// Constructs an AnyTask from the provided Task. | |
| /// The provided task is held strongly until AnyTask is | |
| /// deinitted. | |
| /// - Parameter task: The task to construct with. | |
| init<S, E>(_ task: Task<S, E>) { | |
| cancel = task.cancel | |
| isCancelledBlock = { task.isCancelled } | |
| } | |
| } | |
| extension Task { | |
| var eraseToAnyTask: AnyTask { .init(self) } | |
| } | |
| extension Array where Element == Task<Void, Never> { | |
| var erased: [AnyTask] { map(\.eraseToAnyTask) } | |
| } |
For usage convenience…
Task {
// ...
}.store(in: &tasks)extension Task {
func store<C>(in collection: inout C) where C: RangeReplaceableCollection, C.Element == AnyTask {
collection.append(eraseToAnyTask)
}
}
Nice! Thanks for that!
I've turned this into a Swift Package with test coverage: https://github.com/KaneCheshire/AnyTask
Perfect. I appreciate the effort @KaneCheshire. I’ll be switching to the package.
You can also take advantage of the flexibility of AnyCancellable and conform Task to the Cancellable protocol:
extension Task: Cancellable {} This offers all of the same functionality:
let task = Task { ... }
// Wrap task in AnyCancellable:
let cancellable = AnyCancellable(task)
// Or use the store(in:) extension method, which we get for free:
var cancellables = Set<AnyCancellable>()
task.store(in: &cancellables)This works because Task already implements a cancel method, which is the only requirement of the Cancellable protocol.
Here's some Playground code if you want to mess around with this:
import UIKit
import Combine
extension Task: Cancellable {}
let emitter = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
let task = Task {
for await value in emitter.values {
print("tick: \(value)")
}
}
var cancel: AnyCancellable? = AnyCancellable(task)
DispatchQueue.main.asyncAfter(deadline: .now() + 4) {
// The print statements will stop after 4 seconds when the cancellable is deallocated.
cancel = nil
}
RunLoop.main.run() // Playground will run until stopped.
That’s nice! But means there’s a dependency on Combine which is a system library and not a language library right?
Yes, that’s correct!
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I dunno why the indentation is so large, GitHub keeps reverting is 🤷