A `Publisher.collect(_:)` example.

publisher_collect.swift

import CombineExt

let delayedIntPublishers = (0...12).map { index in
	AnyPublisher<Int, Never>.create { subscriber in
		print("Subscribed to \(index)")

		DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
			subscriber.send(index)
			subscriber.send(completion: .finished)
		}

		return AnyCancellable {}
	}
}

let cancellable = delayedIntPublishers
	.publisher
	.flatMap { $0 }
	.collect(5)
	.sink(receiveValue: { batch in print(batch) })

// Outputs:
// ```
// Subscribed to 0
// Subscribed to 1
// Subscribed to 2
// Subscribed to 3
// Subscribed to 4
// Subscribed to 5
// Subscribed to 6
// Subscribed to 7
// Subscribed to 8
// Subscribed to 9
// Subscribed to 10
// Subscribed to 11
// Subscribed to 12
// ```
// and then two seconds later,
// ```
// [0, 1, 2, 3, 4]
// [5, 6, 7, 8, 9]
// [10, 11, 12]
// ```