zip(_:_:_:)
Combines elements from three other publishers and delivers groups of elements as tuples.
Declaration
func zip<P, Q, R>(_ publisher1: P, _ publisher2: Q, _ publisher3: R) -> Publishers.Zip4<Self, P, Q, R> where P : Publisher, Q : Publisher, R : Publisher, Self.Failure == P.Failure, P.Failure == Q.Failure, Q.Failure == R.FailureParameters
- publisher1:
A second publisher.
- publisher2:
A third publisher.
- publisher3:
A fourth publisher.
Return Value
A publisher that emits groups of elements from the upstream publishers as tuples.
Discussion
Use zip(_:_:_:) to return a new publisher that combines the elements from three other publishers to publish a tuple to the downstream subscriber. The returned publisher waits until all four publishers have emitted an event, then delivers the oldest unconsumed event from each publisher as a tuple to the subscriber.
In this example, several PassthroughSubject instances emit values; zip(_:_:_:) receives the oldest unconsumed value from each publisher and combines them into a tuple that it republishes to the downstream:
let numbersPub = PassthroughSubject<Int, Never>()
let lettersPub = PassthroughSubject<String, Never>()
let emojiPub = PassthroughSubject<String, Never>()
let fractionsPub = PassthroughSubject<Double, Never>()
cancellable = numbersPub
.zip(lettersPub, emojiPub, fractionsPub)
.sink { print("\($0)") }
numbersPub.send(1) // numbersPub: 1 lettersPub: emojiPub: fractionsPub: zip output: <none>
numbersPub.send(2) // numbersPub: 1,2 lettersPub: emojiPub: fractionsPub: zip output: <none>
numbersPub.send(3) // numbersPub: 1,2,3 lettersPub: emojiPub: fractionsPub: zip output: <none>
fractionsPub.send(0.1) // numbersPub: 1,2,3 lettersPub: "A" emojiPub: fractionsPub: 0.1 zip output: <none>
lettersPub.send("A") // numbersPub: 1,2,3 lettersPub: "A" emojiPub: fractionsPub: 0.1 zip output: <none>
emojiPub.send("😀") // numbersPub: 2,3 lettersPub: "A" emojiPub: "😀" fractionsPub: 0.1 zip output: (1, "A", "😀", 0.1)
lettersPub.send("B") // numbersPub: 2,3 lettersPub: "B" emojiPub: fractionsPub: zip output: <none>
fractionsPub.send(0.8) // numbersPub: 2,3 lettersPub: "B" emojiPub: fractionsPub: 0.8 zip output: <none>
emojiPub.send("🥰") // numbersPub: 3 lettersPub: "B" emojiPub: fractionsPub: 0.8 zip output: (2, "B", "🥰", 0.8)
// Prints:
// (1, "A", "😀", 0.1)
// (2, "B", "🥰", 0.8)If any upstream publisher finishes successfully or fails with an error, so too does the zipped publisher.