---
title: IOAsyncCallback
framework: iokit
role: symbol
role_heading: Type Alias
path: iokit/ioasynccallback
---

# IOAsyncCallback

standard callback function for asynchronous I/O requests with lots of extra arguments beyond a refcon and result code.

## Declaration

```swift
typealias IOAsyncCallback = (UnsafeMutableRawPointer?, IOReturn, UnsafeMutablePointer<UnsafeMutableRawPointer?>?, UInt32) -> Void
```

## Parameters

- `refcon`: The refcon passed into the original I/O request
- `result`: The result of the I/O operation
- `args`: Array of extra arguments
- `numArgs`: Number of extra arguments

## See Also

### Callbacks

- [IOAsyncCallback0](iokit/ioasynccallback0.md)
- [IOAsyncCallback1](iokit/ioasynccallback1.md)
- [IOAsyncCallback2](iokit/ioasynccallback2.md)
- [IOServiceInterestCallback](iokit/ioserviceinterestcallback.md)
- [IOServiceMatchingCallback](iokit/ioservicematchingcallback.md)