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# Subject

A publisher that exposes a method for outside callers to publish elements.

```
protocol Subject<Output, Failure> : AnyObject, Publisher
```

## Overview

A subject is a publisher that you can use to ”inject” values into a stream, by calling its [`send(_:)`](/documentation/Combine/Subject/send(_:)) method. This can be useful for adapting existing imperative code to the Combine model.

## Topics

### Delivering elements to subscribers

[`send(_:)`](/documentation/Combine/Subject/send(_:))

Sends a value to the subscriber.

[`send()`](/documentation/Combine/Subject/send())

Sends a void value to the subscriber.

### Delivering life cycle events to subscribers

[`send(subscription:)`](/documentation/Combine/Subject/send(subscription:))

Sends a subscription to the subscriber.

[`send(completion:)`](/documentation/Combine/Subject/send(completion:))

Sends a completion signal to the subscriber.


---

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