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# Publishers.MapError

A publisher that converts any failure from the upstream publisher into a new error.

```
struct MapError<Upstream, Failure> where Upstream : Publisher, Failure : Error
```

## Topics

### Creating an error-mapping publisher

[`init(upstream:_:)`](/documentation/Combine/Publishers/MapError/init(upstream:_:))

[`init(upstream:transform:)`](/documentation/Combine/Publishers/MapError/init(upstream:transform:))

Creates a publisher that converts any failure from the upstream publisher into a new error.

### Declaring supporting types

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

The kind of values published by this publisher.

### Inspecting publisher properties

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

The publisher from which this publisher receives elements.

[`transform`](/documentation/Combine/Publishers/MapError/transform)

The closure that converts the upstream failure into a new error.


---

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