Batch subscribing and outputting in Combine.

batch_subscribing_and_outputting.swift

import CombineExt

extension Collection where Element: Publisher {
	func batchedSubscribe(by limit: Int) -> AnyPublisher<[Element.Output], Element.Failure> {
		let indexBreaks = sequence(
			first: startIndex,
			next: {
				$0 == endIndex ?
					nil :
					index($0, offsetBy: limit, limitedBy: endIndex)
						?? endIndex
			}
		)

		return Swift.zip(indexBreaks, indexBreaks.dropFirst())
			.map(..<)
			.publisher
			.setFailureType(to: Element.Failure.self)
			.flatMap(maxPublishers: .max(1)) { self[$0].zip() }
			.eraseToAnyPublisher()
	}
}