Swift 2 – UnsafeMutablePointer to object

by

This should work: pass the object pointer as an opaque unmanaged pointer
to the callback:

context.info = UnsafeMutablePointer(Unmanaged.passUnretained(myObject).toOpaque())
SCNetworkReachabilitySetCallback(reachability, callback, &context)

and retrieve in the callback via:

func callback(reachability:SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutablePointer<Void>) {

    let myObject = Unmanaged<MyObject>.fromOpaque(COpaquePointer(info)).takeUnretainedValue()

}

Of course this assumes that some strong reference to the object exists
as long as the callback is installed, so that the object is not
deallocated.

Update: Note that both conversions from object pointer to void pointer
and back can be simplified if you are willing to use “unsafe” functions:

context.info = unsafeAddressOf(myObject)
// ...
myObject = unsafeBitCast(info, MyObject.self)

The generated assembly code is – as far as I can see – identical.

Update 2: See also How to cast self to UnsafeMutablePointer<Void> type in swift for more information
about the “bridging” and some helper functions which can be used here.

Swift 3 update (Xcode 8 beta 6): 

var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
context.info = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())

// ...

func callback(reachability:SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutableRawPointer?) {
    if let info = info {
        let myObject = Unmanaged<MyObject>.fromOpaque(info).takeUnretainedValue()
        // ...
    }
}

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