<!--
{
  "availability" : [
    "iOS: 13.0.0 -",
    "iPadOS: 13.0.0 -",
    "macCatalyst: 13.0.0 -",
    "macOS: 10.15.0 -",
    "tvOS: 13.0.0 -",
    "visionOS: 1.0.0 -",
    "watchOS: 6.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "Combine",
  "identifier" : "/documentation/Combine/Publishers/Multicast/init(upstream:createSubject:)",
  "metadataVersion" : "0.1.0",
  "role" : "Initializer",
  "symbol" : {
    "kind" : "Initializer",
    "modules" : [
      "Combine"
    ],
    "preciseIdentifier" : "s:7Combine10PublishersO9MulticastC8upstream13createSubjectAEy_xq_Gx_q_yctcfc"
  },
  "title" : "init(upstream:createSubject:)"
}
-->

# init(upstream:createSubject:)

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

```
init(upstream: Upstream, createSubject: @escaping () -> SubjectType)
```

## Parameters

`createSubject`

A closure that returns a [`Subject`](/documentation/Combine/Subject) each time a subscriber attaches to the multicast publisher.

---

Copyright &copy; 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)