Question

我正在将本实验中的一些C＃重写为F＃：https://github.com/Microsoft/TechnicalCommunityContent/tree/master/IoT/Azure%20Stream%20Analytics/Session%202%20-%20Hands%20On

我正在练习6，＃17 - 创建SimpleEventProcessor类型我想实现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()
    | _ -> ()

但我有两个问题：

如何在F＃world中返回等待？
如何退回NOT案例 - ＆gt; C＃只是忽略了这种可能性。

Answer 1

如果值的类型为Async<'T>，则可以不带任何关键字返回。如果类型为Task或Task<'T>，则可以|> Async.AwaitTask。
您可以返回async { return () }。

所以你明白了：

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 () }

另一种可能性是将整个块放在async工作流程中，并将return!用于1，将return用于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 ()
    }

事实上，使用异步工作流可以让您放弃{C}的()案例：

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
    }

F＃中的异步等待

1 个答案: