`ReplaySubject` with filled-in `.send(subscription:)` requirement.

replay_subject_send_subscription.swift

final class ReplaySubject<Output, Failure: Error>: Subject {
	typealias Output = Output
	typealias Failure = Failure

	private let bufferSize: Int

	init(bufferSize: Int) {
		self.bufferSize = bufferSize
	}

	func send(subscription: Combine.Subscription) {
		subscription.request(.unlimited)
	}

	func send(completion: Subscribers.Completion<Failure>) { /* … */ }

	func send(_ value: Output) { /* … */ }

	func receive<Subscriber: Combine.Subscriber>(
		subscriber: Subscriber
	) where Failure == Subscriber.Failure, Output == Subscriber.Input { /* … */ }
}

extension ReplaySubject {
	final class Subscription: Combine.Subscription {
		func request(_ demand: Subscribers.Demand) { /* … */ }

		func cancel() { /* … */ }
	}
}