异步等待在F＃

Question

我重写了一些C＃在这个实验室中F＃：https://github.com/Microsoft/TechnicalCommunityContent/tree/master/IoT/Azure%20Stream%20Analytics/Session%202%20-%20Hands%20On

我在练习6，＃17 - 创建SimpleEventProcessor类型。
我要实现的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(); 
     } 
    } 

，我开始是这样的：

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个问题：

1. 我怎么回在F＃世界等待？
2. 如何返回NOT情况 - > C＃只是忽略这种可能性。

Answer 1

1. 如果值的类型Async<'T>，你可以只返回它没有任何关键字。如果它有Task或Task<'T>，则可以执行|> Async.AwaitTask。

2. 您可以返回async { return() }。

所以，你得到这样的：

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() } 

另一种可能是把整个块在async工作流程，并使用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() 
    } 

在事实上，使用异步工作流程允许您类似于C＃删除()的情况：

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 
    }