如何定义函数的返回类型/输出类型 [英] How to define the return type / OutputType of a function

问题描述

为什么下面是变化的类型?

Why is the following changing type?

function SomeFunction($SomeParameter){
    return $SomeParameter
}

我想我需要设置返回类型，但如何设置?

I guess I need to set a return type, but how?

一个例子是:

$NewFolder=Join-Path $CurrentFolder -ChildPath $FolderName
$Tmp=SomeFunction($NewFolder)

现在 $Tmp 是一个数组而不仅仅是一个路径

Now $Tmp is an array and not just a path

推荐答案

您的问题与设计"有关.PowerShell 将分块返回一个数组，以便可以将其转发到 PowerShell 管道.

Your issue is per "design". PowerShell will return an array in chunks so that it can be forwarded the PowerShell pipeline.

示例:

 SomeFunction -SomeParameter @(1,2,3,4) | Where-Object { $_ -gt 2 }

如果没有这种行为，就不可能将函数的输出流水线化到另一个函数/cmdlet.

Without this behavior pipelining the output of the function to another function/cmdlet won't be possible.

如果你想返回一个数组，你可以将代码改为:

If you want to return an array you can change to code to:

 function SomeFunction($SomeParameter){
    <#
     # Through the unary operator we can return an array with one entry.
     # This entry contains the original array.
     #>
    ,$SomeParameter
}

另一种选择是在调用端使用 @():

Another option would be the use of @() when at the calling side:

function SomeFunction($SomeParameter){
    # return to pipelin
    $SomeParameter
}

$array = @(SomeFunction -SomeParameter 1,2,3,4)

还有这个 reddit answer 解释了更多细节.

There is also this reddit answer explaining the behavior in more detail.

希望有所帮助.

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