# combineLatest(_:_:_:) Subscribes to two additional publishers and invokes a closure upon receiving output from any of the publishers. ``` func combineLatest(_ publisher1: P, _ publisher2: Q, _ transform: @escaping (Self.Output, P.Output, Q.Output) -> T) -> Publishers.Map, T> where P : Publisher, Q : Publisher, Self.Failure == P.Failure, P.Failure == Q.Failure ``` ## Parameters `publisher1` A second publisher to combine with the first publisher. `publisher2` A third publisher to combine with the first publisher. `transform` A closure that receives the most-recent value from each publisher and returns a new value to publish. ## Return Value A publisher that receives and combines elements from this publisher and two other publishers. ## Discussion Use `combineLatest(_:,_:)` to combine the current and two additional publishers and transform them using a closure you specify to publish a new value to the downstream. > Tip: The combined publisher doesn’t produce elements until each of its upstream publishers publishes at least one element. The combined publisher passes through any requests to *all* upstream publishers. However, it still obeys the demand-fulfilling rule of only sending the request amount downstream. If the demand isn’t `.unlimited`, it drops values from upstream publishers. It implements this by using a buffer size of 1 for each upstream, and holds the most-recent value in each buffer. All upstream publishers need to finish for this publisher to finish. If an upstream publisher never publishes a value, this publisher never finishes. If any of the combined publishers terminates with a failure, this publisher also fails. In the example below, `combineLatest()` receives the most-recent values published by three publishers, multiplies them together, and republishes the result: ``` let pub = PassthroughSubject() let pub2 = PassthroughSubject() let pub3 = PassthroughSubject() cancellable = pub .combineLatest(pub2, pub3) { firstValue, secondValue, thirdValue in return firstValue * secondValue * thirdValue } .sink { print("Result: \($0).") } pub.send(1) pub.send(2) pub2.send(2) pub3.send(10) pub.send(9) pub3.send(4) pub2.send(12) // Prints: // Result: 40. // pub = 2, pub2 = 2, pub3 = 10 // Result: 180. // pub = 9, pub2 = 2, pub3 = 10 // Result: 72. // pub = 9, pub2 = 2, pub3 = 4 // Result: 432. // pub = 9, pub2 = 12, pub3 = 4 ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)