dispatch-sync-safe.swift

func dispatch_sync<R> (queue: dispatch_queue_t, block: Void -> R ) -> R {
  var result: R!
  dispatch_sync(queue) {
    result = block()
  }
  return result
}

func result() -> String {
  return
    dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
      return "something"
  }
}