---
title: "multicast(_:)"
framework: combine
role: symbol
role_heading: Instance Method
path: "combine/publisher/multicast(_:)"
---

# multicast(_:)

Applies a closure to create a subject that delivers elements to subscribers.

## Declaration

```swift
func multicast<S>(_ createSubject: @escaping () -> S) -> Publishers.Multicast<Self, S> where S : Subject, Self.Failure == S.Failure, Self.Output == S.Output
```

## Parameters

- `createSubject`: A closure to create a new doc://com.apple.Combine/documentation/Combine/Subject each time a subscriber attaches to the multicast publisher.

## Discussion

Discussion Use a multicast publisher when you have multiple downstream subscribers, but you want upstream publishers to only process one 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:), this method produces a publisher that creates a separate Subject for each subscriber. The following example uses a sequence publisher as a counter to publish three random numbers, generated by a map(_:) operator. It uses a multicast(_:) operator whose closure creates a PassthroughSubject to share the same random number to each of two subscribers. Because the multicast publisher is a ConnectablePublisher, publishing only begins after a call to 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:) operator receives each random value only one time, and then sends the value to both subscribers.

## See Also

### Working with multiple subscribers

- [multicast(subject:)](combine/publisher/multicast(subject:).md)
- [share()](combine/publisher/share().md)