Combine: One-shot subscriptions

OneShotSubscription.swift

// Credit: https://www.apeth.com/UnderstandingCombine/subscribers/subscribersoneshot.html

var cancellable: AnyCancellable? 
cancellable = pub.sink(receiveCompletion: {_ in 
    cancellable?.cancel()
}) { image in
    self.imageView.image = image
}

// Or just subscribe to the Subscribers.Sink: 
// https://stackoverflow.com/questions/61216852/whats-the-difference-between-sink-and-subscribers-sink
pub.subscribe(
    Subscribers.Sink(
        receiveCompletion: { _ in },
        receiveValue: { _ in }
    )
)