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# Publishers.Multicast

A publisher that uses a subject to deliver elements to multiple subscribers.

```
final class Multicast<Upstream, SubjectType> where Upstream : Publisher, SubjectType : Subject, Upstream.Failure == SubjectType.Failure, Upstream.Output == SubjectType.Output
```

## Overview

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.

## Topics

### Creating a multicast publisher

[`init(upstream:createSubject:)`](/documentation/Combine/Publishers/Multicast/init(upstream:createSubject:))

Creates a multicast publisher that applies a closure to create a subject that delivers elements to subscribers.

### Declaring supporting types

[`Publishers.Multicast.Output`](/documentation/Combine/Publishers/Multicast/Output)

The kind of values published by this publisher.

[`Publishers.Multicast.Failure`](/documentation/Combine/Publishers/Multicast/Failure)

The kind of errors this publisher might publish.

### Inspecting publisher properties

[`upstream`](/documentation/Combine/Publishers/Multicast/upstream)

The publisher from which this publisher receives its elements.

[`createSubject`](/documentation/Combine/Publishers/Multicast/createSubject)

A closure that returns a subject each time a subscriber attaches to the multicast publisher.


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