Combine - Remove pipeline from container - swift

Question

Assume the following simplified code-snippet
import Foundation
import Combine
public class NetworkFetch {
fileprivate var networkPipelines : Set<AnyCancellable> = []
public func loadDataFor(url : URL)
{
URLSession.shared.dataTaskPublisher(for: url)
.map { $0.data }
.decode(type: City.self, decoder: JSONDecoder())
.eraseToAnyPublisher()
.sink(receiveCompletion: {_ in print("Finish")},
receiveValue: { v in
print("\(c)\n")
}
)
.store(in: &networkPipelines)
}
}
For each call of loadDataFor a new combine-pipeline is generated and added to the networkPipelines container. This container grows over time.
What is the correct way to remove such an URLSession-pipeline from this container as soon as all data is fetched by the URLSession-pipeline?

Answer 1

One thing you could do is remove your own subscription from inside sink:
But perhaps the better approach is to subscribe to a PassthroughSubject one time and send the requested URL and the callback through it:
private let subject = PassthroughSubject<(URL, (City) -> Void)), Never>()
private var c: Set<AnyCancellable> = []
init() {
subject
.flatMap { (url, callback) in
URLSession.shared.dataTaskPublisher(for: url)
.map(\.data)
.decode(type: City.self, decoder: JSONDecoder())
.zip(Just(callback).setFailureType(to: Error.self))
}
.sink(receiveCompletion: {_ in print("Finish")},
receiveValue: { (city, callback) in
callback(city)
}
)
.store(in: &c)
}
public func loadDataFor(url : URL, callback: #escaping (City) -> Void) {
subject.send(url, callback)
}
So, a single subscription can handle multiple requests by sending a pair of the requested URL and the callback through the subject.