MIDIClientPOC.swift

import XCPlayground
import CoreMIDI

XCPSetExecutionShouldContinueIndefinitely(true)

func notifyProc(a: UnsafePointer<MIDINotification>, b: UnsafeMutablePointer<Void>) -> Void {
    let notification = a[0]
    notification.messageID
    notification.messageSize
}

var client = MIDIClientRef()
let status = withUnsafeMutablePointer(&client) {
    return MIDIClientCreate("SwiftMIDI", notifyProc, nil, $0)
}