<!--
{
  "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/Future/Promise",
  "metadataVersion" : "0.1.0",
  "role" : "Type Alias",
  "symbol" : {
    "kind" : "Type Alias",
    "modules" : [
      "Combine"
    ],
    "preciseIdentifier" : "s:7Combine6FutureC7Promisea"
  },
  "title" : "Future.Promise"
}
-->

# Future.Promise

A type that represents a closure to invoke in the future, when an element or error is available.

```
typealias Promise = (Result<Output, Failure>) -> Void
```

## Discussion

The promise closure receives one parameter: a `Result` that contains either a single element published by a [`Future`](/documentation/Combine/Future), or an error.

---

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)