# setFailureType(to:) Changes the failure type declared by the upstream publisher. ``` func setFailureType(to failureType: E.Type) -> Publishers.SetFailureType where E : Error ``` ## Parameters `failureType` The `Failure` type presented by this publisher. ## Return Value A publisher that appears to send the specified failure type. ## Discussion Use [`setFailureType(to:)`](/documentation/Combine/Publisher/setFailureType(to:)) when you need set the error type of a publisher that cannot fail. Conversely, if the upstream can fail, you would use [`mapError(_:)`](/documentation/Combine/Publisher/mapError(_:)) to provide instructions on converting the error types to needed by the downstream publisher’s inputs. The following example has two publishers with mismatched error types: `pub1`’s error type is , and `pub2`’s error type is . Because of the mismatch, the [`combineLatest(_:)`](/documentation/Combine/Publisher/combineLatest(_:)) operator requires that `pub1` use [`setFailureType(to:)`](/documentation/Combine/Publisher/setFailureType(to:)) to make it appear that `pub1` can produce the type, like `pub2` can. ``` let pub1 = [0, 1, 2, 3, 4, 5].publisher let pub2 = CurrentValueSubject(0) let cancellable = pub1 .setFailureType(to: Error.self) .combineLatest(pub2) .sink( receiveCompletion: { print ("completed: \($0)") }, receiveValue: { print ("value: \($0)")} ) // Prints: "value: (5, 0)". ``` --- 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)