Using Swift CFunctionPointer to pass a callback to CoreMIDI API

Question

It may be that this is actually not possible currently, which would be unfortunate. I\'m trying to call the CoreMIDI API to set up a MIDI input. This is what I\'m trying to

Answer 1

Swift 1.x (Old Way)

There's a way to do that - Objective-C Runtime is the trick.

import CoreMIDI

let block : @objc_block
(UnsafePointer,
UnsafeMutablePointer,
UnsafeMutablePointer) -> Void =
{ (pktlist,readProcRefCon,srcConnRefCon) in

    //Your code goes here...
}

let imp : COpaquePointer =
    imp_implementationWithBlock(unsafeBitCast(block, AnyObject.self))

let callback : MIDIReadProc = unsafeBitCast(imp, MIDIReadProc.self)

Works with CoreFoundation callbacks. Should work for CoreMIDI too.

---

Swift 2.x (New Way)

In Swift 2 the process becomes "less hacky" (and slightly more readable).

import CoreMIDI

let callback : @convention(c) (pktlist : UnsafePointer,
                               readProcRefCon : UnsafeMutablePointer,
                               srcConnRefCon : UnsafeMutablePointer) -> Void =

{ (pktlist, readProcRefCon, srcConRefCon) in

}

let usableCallback = unsafeBitCast(callback, MIDIReadProc.self)