为什么我不能在语句中将 Await 括在括号中? [英] Why can't I wrap Await in parenthesis in a statement?

问题描述

在 C# 中，我有一些代码如下:

In C#, I have some code that looks like:

(await GetBoolAsync()).ShouldBeTrue();

ShouldBeTrue() 是来自 Shouldly 库的扩展方法关于布尔值.

ShouldBeTrue() is an extension method from the Shouldly library that operates on Booleans.

VB.NET 似乎不喜欢将 Await 关键字括在括号中:

VB.NET doesn't seem to like wrapping the Await keyword in parenthesis:

(Await GetBoolAsync()).ShouldBeTrue()

编译器在行首的左括号中报告语法错误.我可以通过声明一个中间变量来解决这个问题，但是有没有办法像 C# 这样在一行中实现这一点?

The compiler reports a syntax error on the opening parenthesis at the beginning of the line. I can work around it by declaring an intermediate variable, but is there a way to achieve this in one line like C#?

一个完整的控制台应用程序来重现这个:

A full console application to reproduce this:

Imports System.Runtime.CompilerServices

Module Module1

    Sub Main
    End Sub

    Async Function Test() As Task
        (Await GetBoolAsync()).ShouldBeTrue()
    End Function

    Function GetBoolAsync() As Task(Of Boolean)
        Return Task.FromResult(True)
    End Function

    <Extension()>
    Public Sub ShouldBeTrue(x As Boolean)
    End Sub

End Module

该错误非常无用:

错误 BC30035:语法错误.

error BC30035: Syntax error.

推荐答案

这样做有一个特殊的语法 - 你应该使用 Call 关键字:

There is a special syntax for doing so - you should use the Call keyword:

Async Function Test() As Task
    Call (Await GetBoolAsync()).ShouldBeTrue()
End Function

那是因为您不能像在 C# 中那样在 Visual Basic 中直接调用非文字表达式的成员:

That's because you cannot directly call a member of non-literal expression in Visual Basic, like you would in C#:

(5).ToString() 'It is wrong!

在这种特殊情况下，这包括 Await 的结果.

And in this particular case this includes the result of Await.

希望有帮助！

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