private static IEnumerator<Int32> FetchStockQuotesAsyncEnumerator(AsyncEnumerator ae, WebService svc)
 {
     svc.BeginFetchStockQuotes(ae.End(), null);
     yield return 1;
     IStockQuote qt = svc.EndFetchStockQuotes(ae.DequeueAsyncResult());
 }
        // IAsyncResult interface (APM).
#if AsyncEnumerator
        private static void FetchStockQuotesApm(WebService svc)
        {
            // This never blocks. Your code returns immediately.
            svc.BeginFetchStockQuotes(FetchStockQuotesApmCallback, svc);
        }