gistfile1.swift

import Foundation

let notification  = "MyNotification"

struct DontCopy {
    var value = false
    
    mutating func whatever(#callback:() -> ()) {
        self.value = true
        NSNotificationCenter.defaultCenter().addObserverForName(notification, object: nil, queue: nil) { (noti) -> Void in
            self.value = false
            callback()
        }
    }
}

var dc = DontCopy()
assert(dc.value == false)

dc.whatever { () -> () in
    println("Value in callback is \(dc.value)")
}

assert(dc.value == true)

NSNotificationCenter.defaultCenter().postNotificationName(notification, object: nil)

println("Value out of callback is \(dc.value)")