In this article, we will explore six handy combining operators in Combine. We will do so by quickly experimenting with each of them in an Xcode Playground.

The source code is available at the bottom of the article.

Without further ado, let’s get started.

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1. prepend

This group of operators allows us to prepend events, values, or other publishers to our source publisher:

import Foundation
	import Combine

	var subscriptions = Set<AnyCancellable>()

	func prependOutputExample() {
	    let stringPublisher = ["World!"].publisher

	    stringPublisher
	        .prepend("Hello")
	        .sink(receiveValue: { print($0) })
	        .store(in: &subscriptions)
	}

The result is Hello and World! printed in sequential order:

Let’s now prepend another publisher of the same type:

func prependPublisherExample() {
	    let subject = PassthroughSubject<String, Never>()
	    let stringPublisher = ["Break things!"].publisher

	    stringPublisher
	        .prepend(subject)
	        .sink(receiveValue: { print($0) })
	        .store(in: &subscriptions)

	    subject.send("Run code")
	    subject.send(completion: .finished)
	}

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