Created
September 29, 2020 11:23
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Swift combine StartWith
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extension Publisher { | |
func unwrap() -> Publishers.CompactMap<Self, Self.Output> { | |
return compactMap({ $0 }) | |
} | |
func startWith1(_ value: Self.Output) -> Publishers.Merge<AnyPublisher<Self.Output, Self.Failure>, Self> { | |
return Publishers.Merge(Just(value).setFailureType(to: Self.Failure.self).eraseToAnyPublisher(), self) | |
} | |
func startWith(_ value: Self.Output) -> Publishers.StartWith<Self> { | |
return Publishers.StartWith(upstream: self, output: value) | |
} | |
} |
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extension Publishers { | |
struct StartWith<Upstream>: Publisher where Upstream : Publisher { | |
typealias Output = Upstream.Output | |
typealias Failure = Upstream.Failure | |
let output: Output | |
/// The publisher from which this publisher receives elements. | |
let upstream: Upstream | |
public init(upstream: Upstream, output: Self.Output) { | |
self.upstream = upstream | |
self.output = output | |
} | |
func receive<S>(subscriber: S) where S : Combine.Subscriber, Self.Failure == S.Failure, Self.Output == S.Input { | |
let subs = Subscription(upstream: upstream, downstream: subscriber, output: output) | |
subscriber.receive(subscription: subs) | |
} | |
} | |
} | |
extension Publishers.StartWith { | |
class Subscription<Downstream: Combine.Subscriber>: Combine.Subscription where Downstream.Input == Output, Downstream.Failure == Failure { | |
private var sink: Subscriber<Upstream, Downstream>? | |
private let output: Upstream.Output | |
init(upstream: Upstream, downstream: Downstream, output: Upstream.Output) { | |
self.sink = Subscriber(upstream: upstream, downstream: downstream) | |
self.output = output | |
} | |
func request(_ demand: Subscribers.Demand) { | |
_ = sink?.receive(output) | |
} | |
func cancel() { | |
sink = nil | |
} | |
} | |
} | |
extension Publishers.StartWith { | |
class Subscriber<Upstream, Downstream>: Combine.Subscriber where | |
Upstream : Publisher, | |
Downstream : Combine.Subscriber, | |
Upstream.Output == Downstream.Input, | |
Upstream.Failure == Downstream.Failure { | |
typealias Input = Upstream.Output | |
typealias Failure = Upstream.Failure | |
private var downstream: Downstream | |
private var demand = Subscribers.Demand.unlimited | |
init(upstream: Upstream, downstream: Downstream) { | |
self.downstream = downstream | |
upstream.subscribe(self) | |
} | |
func receive(subscription: Combine.Subscription) { | |
subscription.request(.unlimited) | |
} | |
func receive(_ input: Upstream.Output) -> Subscribers.Demand { | |
return downstream.receive(input) | |
} | |
func receive(completion: Subscribers.Completion<Upstream.Failure>) { | |
downstream.receive(completion: completion) | |
} | |
} | |
} |
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final class IntSubscriber: Subscriber { | |
typealias Input = Int | |
typealias Failure = Never | |
func receive(subscription: Subscription) { | |
subscription.request(.max(2)) | |
} | |
func receive(_ input: Int) -> Subscribers.Demand { | |
print("Received value", input) | |
return .none | |
} | |
func receive(completion: Subscribers.Completion<Never>) { | |
print("Received completion", completion) | |
} | |
} | |
let publisher = PassthroughSubject<Int, Never>() | |
let subscriber = IntSubscriber() | |
publisher | |
.startWith(10) | |
.subscribe(subscriber) | |
publisher.send(7) | |
publisher.send(15) | |
publisher.send(20) |
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