# multicast(_:) Applies a closure to create a subject that delivers elements to subscribers. ``` func multicast(_ createSubject: @escaping () -> S) -> Publishers.Multicast where S : Subject, Self.Failure == S.Failure, Self.Output == S.Output ``` ## Parameters `createSubject` A closure to create a new [`Subject`](/documentation/Combine/Subject) each time a subscriber attaches to the multicast publisher. ## Discussion Use a multicast publisher when you have multiple downstream subscribers, but you want upstream publishers to only process one [`receive(_:)`](/documentation/Combine/Subscriber/receive(_:)) call per event. This is useful when upstream publishers are doing expensive work you don’t want to duplicate, like performing network requests. In contrast with [`multicast(subject:)`](/documentation/Combine/Publisher/multicast(subject:)), this method produces a publisher that creates a separate [`Subject`](/documentation/Combine/Subject) for each subscriber. The following example uses a sequence publisher as a counter to publish three random numbers, generated by a [`map(_:)`](/documentation/Combine/Publisher/map(_:)-99evh) operator. It uses a [`multicast(_:)`](/documentation/Combine/Publisher/multicast(_:)) operator whose closure creates a [`PassthroughSubject`](/documentation/Combine/PassthroughSubject) to share the same random number to each of two subscribers. Because the multicast publisher is a [`ConnectablePublisher`](/documentation/Combine/ConnectablePublisher), publishing only begins after a call to [`connect()`](/documentation/Combine/ConnectablePublisher/connect()). ``` let pub = ["First", "Second", "Third"].publisher .map( { return ($0, Int.random(in: 0...100)) } ) .print("Random") .multicast { PassthroughSubject<(String, Int), Never>() } cancellable1 = pub .sink { print ("Stream 1 received: \($0)")} cancellable2 = pub .sink { print ("Stream 2 received: \($0)")} pub.connect() // Prints: // Random: receive value: (("First", 9)) // Stream 2 received: ("First", 9) // Stream 1 received: ("First", 9) // Random: receive value: (("Second", 46)) // Stream 2 received: ("Second", 46) // Stream 1 received: ("Second", 46) // Random: receive value: (("Third", 26)) // Stream 2 received: ("Third", 26) // Stream 1 received: ("Third", 26) ``` In this example, the output shows that the [`print(_:to:)`](/documentation/Combine/Publisher/print(_:to:)) operator receives each random value only one time, and then sends the value to both subscribers. --- 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)