異步等待在F＃

Question

我重寫了一些C＃在這個實驗室中F＃：https://github.com/Microsoft/TechnicalCommunityContent/tree/master/IoT/Azure%20Stream%20Analytics/Session%202%20-%20Hands%20On

我在練習6，＃17 - 創建SimpleEventProcessor類型。
我要實現的CloseAsync方法

C＃

async Task IEventProcessor.CloseAsync(PartitionContext context, CloseReason reason) 
    { 
     Debug.WriteLine("Processor Shutting Down. Partition '{0}', Reason: '{1}'.", context.Lease.PartitionId, reason); 
     if (reason == CloseReason.Shutdown) 
     { 
      await context.CheckpointAsync(); 
     } 
    } 

，我開始是這樣的：

member this.CloseAsync(context, reason) = 
    Debug.WriteLine("Processor Shutting Down. Partition '{0}', Reason: '{1}'.", context.Lease.PartitionId, reason) 
    match reason with 
    | CloseReason.Shutdown -> await context.CheckpointAsync() 
    | _ ->() 

，但我有2個問題：

1. 我怎麼回在F＃世界等待？
2. 如何返回NOT情況 - > C＃只是忽略這種可能性。

Answer 1

1. 如果值的類型Async<'T>，你可以只返回它沒有任何關鍵字。如果它有Task或Task<'T>，則可以執行|> Async.AwaitTask。

2. 您可以返回async { return() }。

所以，你得到這樣的：

member this.CloseAsync(context, reason) = 
    Debug.WriteLine("Processor Shutting Down. Partition '{0}', Reason: '{1}'.", context.Lease.PartitionId, reason) 
    match reason with 
    | CloseReason.Shutdown -> context.CheckpointAsync() |> Async.AwaitTask 
    | _ -> async { return() } 

另一種可能是把整個塊在async工作流程，並使用return! 1和return 2：

member this.CloseAsync(context, reason) = 
    async { 
     Debug.WriteLine("Processor Shutting Down. Partition '{0}', Reason: '{1}'.", context.Lease.PartitionId, reason) 
     match reason with 
     | CloseReason.Shutdown -> return! context.CheckpointAsync() |> Async.AwaitTask 
     | _ -> return() 
    } 

在事實上，使用異步工作流程允許您類似於C＃刪除()的情況：

member this.CloseAsync(context, reason) = 
    async { 
     Debug.WriteLine("Processor Shutting Down. Partition '{0}', Reason: '{1}'.", context.Lease.PartitionId, reason) 
     if reason = CloseReason.Shutdown then 
      return! context.CheckpointAsync() |> Async.AwaitTask 
    }