---
title: CFWriteStreamClientCallBack
framework: corefoundation
role: symbol
role_heading: Type Alias
path: corefoundation/cfwritestreamclientcallback
---

# CFWriteStreamClientCallBack

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

## Declaration

```swift
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 doc://com.apple.corefoundation/documentation/CoreFoundation/CFStreamEventType.
- `clientCallBackInfo`: The info member of the doc://com.apple.corefoundation/documentation/CoreFoundation/CFStreamClientContext structure that was used when setting the client for stream.

## Discussion

Discussion This callback is called only for the events requested when setting the client with CFWriteStreamSetClient(_:_:_:_:).