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April 20, 2020 16:00
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Final `ReplaySubject` and `.Subscription` cancellation handling.
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final class ReplaySubject<Output, Failure: Error>: Subject { | |
typealias Output = Output | |
typealias Failure = Failure | |
private let bufferSize: Int | |
private var completion: Subscribers.Completion<Failure>? | |
private var isActive: Bool { /* … */ } | |
private var buffer = [Output]() | |
private var subscriptions = [Subscription<AnySubscriber<Output, Failure>>]() | |
init(bufferSize: Int) { /* … */ } | |
func send(subscription: Combine.Subscription) { /* … */ } | |
func send(completion: Subscribers.Completion<Failure>) { /* … */ } | |
func send(_ value: Output) { /* … */ } | |
func receive<Subscriber: Combine.Subscriber>( | |
subscriber: Subscriber | |
) where Failure == Subscriber.Failure, Output == Subscriber.Input { | |
guard !subscriptions.contains( | |
where: { $0.innerSubscriberIdentifier == subscriber.combineIdentifier } | |
) else { | |
subscriber.receive(subscription: Subscriptions.empty) | |
return | |
} | |
let subscription = Subscription(subscriber: AnySubscriber(subscriber)) { [weak self] in | |
guard | |
let self = self, | |
let subscriptionIndex = self.subscriptions | |
.firstIndex(where: { $0.innerSubscriberIdentifier == subscriber.combineIdentifier }) | |
else { return } | |
self.subscriptions.remove(at: subscriptionIndex) /// (2) The `cancellationHandler` should first | |
/// promote a `weak`ly-captured `self`, check if our subscriber is in `subscriptions` and if so, remove it. | |
} | |
subscriptions.append(subscription) | |
subscriber.receive(subscription: subscription) | |
buffer.forEach(subscription.forward) | |
if let completion = completion { subscription.forward(completion: completion) } | |
} | |
} | |
extension ReplaySubject { | |
final class Subscription<Subscriber: Combine.Subscriber>: Combine.Subscription | |
where Subscriber.Input == Output, Subscriber.Failure == Failure { | |
private var buffer: DemandBuffer<Subscriber>? | |
private var cancellationHandler: (() -> Void)? | |
fileprivate let innerSubscriberIdentifier: CombineIdentifier | |
init( | |
subscriber: Subscriber, | |
cancellationHandler: (() -> Void)? /// (1) I always wondered why _captured_, optional closures | |
/// didn’t need to be tagged `@escaping`—well, it turns out that since `Optional.some` tucks it away | |
/// in an associated value, it’s implicitly escaping. Jesse Squires has [a post with more details](https://www.jessesquires.com/blog/2018/06/10/why-optional-swift-closures-are-escaping/). | |
) { | |
buffer = DemandBuffer(subscriber: subscriber) | |
innerSubscriberIdentifier = subscriber.combineIdentifier | |
self.cancellationHandler = cancellationHandler | |
} | |
func request(_ demand: Subscribers.Demand) { /* … */ } | |
func cancel() { | |
cancellationHandler?() | |
cancellationHandler = nil | |
buffer = nil | |
} | |
func forward(completion: Subscribers.Completion<Failure>) { /* … */ } | |
func forward(value: Output) { /* … */ } | |
} | |
} |
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