Cast a Swift struct to UnsafeMutablePointer<Void>

Question

Is there a way to cast a Swift struct's address to a void UnsafeMutablePointer?
I tried this without success:

struct TheStruct {
    var a:Int = 0
}

var myStruct = TheStruct()
var address = UnsafeMutablePointer<Void>(&myStruct)

Thanks!

EDIT: the context
I am actually trying to port to Swift the first example in Learning CoreAudio.
This is what I have done until now:

func myAQInputCallback(inUserData:UnsafeMutablePointer<Void>,
    inQueue:AudioQueueRef,
    inBuffer:AudioQueueBufferRef,
    inStartTime:UnsafePointer<AudioTimeStamp>,
    inNumPackets:UInt32,
    inPacketDesc:UnsafePointer<AudioStreamPacketDescription>)
 { }

struct MyRecorder {
    var recordFile:     AudioFileID = AudioFileID()
    var recordPacket:   Int64       = 0
    var running:        Boolean     = 0
}

var queue:AudioQueueRef = AudioQueueRef()
AudioQueueNewInput(&asbd,
    myAQInputCallback,
    &recorder,  // <- this is where I *think* a void pointer is demanded
    nil,
    nil,
    UInt32(0),
    &queue)

I am doing efforts to stay in Swift, but if this turns out to be more a problem than an advantage, I will end up linking to a C function.

EDIT: bottome line
If you came to this question because you are trying to use a CoreAudio's AudioQueue in Swift... don't. (read the comments for details)

Answer 1

As far as I know, the shortest way is:

var myStruct = TheStruct()
var address = withUnsafeMutablePointer(&myStruct) {UnsafeMutablePointer<Void>($0)}

But, why you need this? If you want pass it as a parameter, you can (and should):

func foo(arg:UnsafeMutablePointer<Void>) {
    //...
}

var myStruct = TheStruct()
foo(&myStruct)

Answer 2

Most of the method prototypes have been changed as Swift evolved over the years. Here is the syntax for Swift 5:

var struct = TheStruct()

var unsafeMutablePtrToStruct = withUnsafeMutablePointer(to: &struct) {
    $0.withMemoryRebound(to: TheStruct.self, capacity: 1) {
        (unsafePointer: UnsafeMutablePointer<TheStruct>) in

        unsafePointer
    }
}