# breakpointOnError() Raises a debugger signal upon receiving a failure. ``` func breakpointOnError() -> Publishers.Breakpoint ``` ## Return Value A publisher that raises a debugger signal upon receiving a failure. ## Discussion When the upstream publisher fails with an error, this publisher raises the `SIGTRAP` signal, which stops the process in the debugger. Otherwise, this publisher passes through values and completions as-is. In this example a [`PassthroughSubject`](/documentation/Combine/PassthroughSubject) publishes strings, but its downstream [`tryMap(_:)`](/documentation/Combine/Publisher/tryMap(_:)) operator throws an error. This sends the error downstream as a [`Subscribers.Completion.failure(_:)`](/documentation/Combine/Subscribers/Completion/failure(_:)). The [`breakpointOnError()`](/documentation/Combine/Publisher/breakpointOnError()) operator receives this completion and stops the app in the debugger. ``` struct CustomError : Error {} let publisher = PassthroughSubject() cancellable = publisher .tryMap { stringValue in throw CustomError() } .breakpointOnError() .sink( receiveCompletion: { completion in print("Completion: \(String(describing: completion))") }, receiveValue: { aValue in print("Result: \(String(describing: aValue))") } ) publisher.send("TEST DATA") // Prints: "error: Execution was interrupted, reason: signal SIGTRAP." // Depending on your specific environment, the console messages may // also include stack trace information, which is not shown here. ``` --- 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)