---
title: IOAsyncCallback1
framework: iokit
role: symbol
role_heading: Type Alias
path: iokit/ioasynccallback1
---

# IOAsyncCallback1

standard callback function for asynchronous I/O requests with one extra argument beyond a refcon and result code. This is often a count of the number of bytes transferred

## Declaration

```swift
typealias IOAsyncCallback1 = (UnsafeMutableRawPointer?, IOReturn, UnsafeMutableRawPointer?) -> Void
```

## Parameters

- `refcon`: The refcon passed into the original I/O request
- `result`: The result of the I/O operation
- `arg0`: Extra argument

## See Also

### Callbacks

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