Showing how `PassthroughSubject` drops value if there isn’t demand.

passthrough_subject_dropped_values.swift

final class ManualSubscriber: Subscriber {
	var subscription: Subscription?

	func receive(subscription: Subscription) { self.subscription = subscription }
	func receive(_ input: Int) -> Subscribers.Demand { print(input); return .none }
	func receive(completion: Subscribers.Completion<Never>) {}
}

let subscriber = ManualSubscriber()
let subject = PassthroughSubject<Int, Never>()

subject
	.subscribe(subscriber)

subscriber.subscription?.request(.max(1))
subject.send(1)
subject.send(2)
subscriber.subscription?.request(.max(1))
subject.send(3)

// Outputs:
// ```
// 1
// 3
// ```