Proper way to declare ExtAudioFileRef in swift 5 for macOS

Question

I have been working on an audio application where I can seek to a specific point in an ExtAudioFile and load a specific number of frames that represent a particular length (time) of playback into an AVAudioPCMBuffer and start playing it. If the user selects a checkbox during playback of that audio segment, the buffer is then fed the remaining contents of the audio file so it will play to the end.

However, I have hit a roadblock. I have found older examples of code that loads these resources. They way they're declaring the calls is not working in Swift 5 for me. I am getting errors. Specifically:

import Cocoa
import AVFoundation
import AudioToolbox

do {
   var err:OSStatus = noErr
   let url = URL(fileURLWithPath: "./audio files/myAudioFile.mp3")
   let track = try AVAudioFile(forReading: url)
   var trackRef = ExtAudioFileRef?
   err = try ExtAudioFileOpenURL(url as CFURL, trackRef)
} catch {
   print(error)
}

The first error I am getting is for trackRef. The editor is flagging this line as "Expected member name or constructor call after type name." But the example I was following only had the property declared as shown in the code above.

The next line err = try ExtAudioFileOpenURL(orl as CFURL, trackRef) has error "Cannot convert value of type 'ExtAudioFileRef?.Type' (aka 'Optional.Type') to expected argument type 'UnsafeMutablePointer<ExtAudioFileRef?>' (aka 'UnsafeMutablePointer<Optional>')."

The editor is suggesting I change trackRef declaration to ver trackRef = ExtAudioFileRef?() or var trackRef = ExtAudioFileRef?.self but neither of those are any help because if I try using the first suggestion I then get "Cannot invoke initializer for type 'ExtAudioFileRef?' with no arguments" and a gray note showing "1. Overloads for 'ExtAudioFileRef?' exist with these partially matching parameter lists: (Wrapped), (from: Decoder), (nilLiteral: ())." But the error for err = ExtAudioFileOpenURL(url as CFURL, trackRef) goes away. If I try using the second suggestion let trackRef = ExtAudioFileRef?.self there is no error on that line, but then I get an error on the err = ExtAudioFileOpenURL(url as CFURL, trackRef) line that reads "Cannot convert value of type 'ExtAudioFileRef?.Type' (aka 'Optional.Type') to expected argument type 'UnsafeMutablePointer<ExtAudioFileRef?>' (aka 'UnsafeMutablePointer<Optional>')"

I am not versed enough to know what these errors mean as I don't know what UnsafeMutablePointer is. I was just following the example code to try and achieve what I want to do. Unfortunately I've not been able to get any of the audio tools in Swift to do what I want to do and this is the next rabbit hole for me.

Thanks for any help.

Answer 1

I finally found some recent code that uses this in later Swift.

I do not need to initialize the trackRef property, which was what was causing the errors to appear in the declarations. I also didn't need the try method.

Here's the proper way to declare it:

var trackRef: ExtAudioFileRef?
err = ExtAudioFileOpenURL(url as CFURL, &trackRef)

Now for the next rabbit hole...