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# CFWriteStreamClientCallBack

Callback invoked when certain types of activity takes place on a writable stream.

```
typealias CFWriteStreamClientCallBack = (CFWriteStream?, CFStreamEventType, UnsafeMutableRawPointer?) -> Void
```

## Parameters

`stream`

The stream that experienced the event `eventType`.

`eventType`

The event that caused the callback to be called. The possible events are listed in [`CFStreamEventType`](/documentation/CoreFoundation/CFStreamEventType).

`clientCallBackInfo`

The `info` member of the [`CFStreamClientContext`](/documentation/CoreFoundation/CFStreamClientContext) structure that was used when setting the client for `stream`.

## Discussion

This callback is called only for the events requested when setting the client with [`CFWriteStreamSetClient(_:_:_:_:)`](/documentation/CoreFoundation/CFWriteStreamSetClient(_:_:_:_:)).

---

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