我如何等待F#中的异步方法 [英] How do I await an async method in F#

问题描述

如何等待F#中的异步方法?

How do I await an async method in F#?

我有以下代码:

 type LegoExample() = 

    let brick = Brick(BluetoothCommunication("COM3"))
    let! result = brick.ConnectAsync();

错误:

成员定义中出现意外的活页夹关键字

Unexpected binder keyword in member definition

请注意，我查看了以下链接:

Note, I reviewed the following link:

但是，我只观察功能技术而不是OOP技术.

However, I only observe the functional technique and not the OOP technique.

推荐答案

，您会收到错误消息，因为let!构造(就像do!一样)需要放置在计算工作流程中(像async { ...}一样，但还有其他-它基本上是F#为单子提供的语法糖-在C#中，这是LINQ附带的from ... select ...东西，在Haskell中则是do ...块)

you get the error because the let! construct (just like the do!) needs to be placed inside a computational workflow (like async { ...} but there are others - it's basically the syntactic sugar F# gives you for monads - in C# it would be the from ... select ... stuff LINQ came with and in Haskell it would be do ... blocks)

因此，假设brick.ConnectAsync()确实会返回某些Async<...>，那么您可以像这样使用Async.RunSynchronously wait :

so assuming brick.ConnectAsync() will return indeed some Async<...> then you can wait for it using Async.RunSynchronously like this:

let brick = Brick(BluetoothCommunication("COM3"))
let result = brick.ConnectAsync() |> RunSynchronously

遗憾的是，在您链接的页面上进行的快速浏览器搜索未找到ConnectAsync，因此我无法确切告诉您代码段的缩进位置，但是您很可能希望将其包含在这样的async { ... }块中:

sadly a quick browser search on the page you linked did not find ConnectAsync so I cannot tell you exactly what the indent of the snippet was here but most likely you wanted to have this inside a async { ... } block like this:

let myAsyncComputation =
    async {
        let brick = Brick(BluetoothCommunication "COM3")
        let! result = brick.ConnectAsync()
        // do something with result ...
    }

(请注意，我删除了一些不必要的括号等)

(note that I remove some unnecessary parentheses etc.)

，然后您可以使用此myAsyncComputation

• 在另一个async { .. }工作流程中
• 使用Async.RunSynchronously运行并等待它
• 与Async.Start一起在后台运行(为此，您的代码块必须输入Async<unit>类型
• 使用Async.StartAsTask启动并从中获取Task<...>
• ...

• inside yet another async { .. } workflow
• with Async.RunSynchronously to run and await it
• with Async.Start to run it in background (your block needs to have type Async<unit> for this
• with Async.StartAsTask to start and get a Task<...> out of it
• ...

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