保留PowerShell函数的返回类型 [英] Preserving PowerShell function return type

问题描述

在PowerShell脚本中，我需要使用以下签名调用.NET方法：

In my PowerShell script I need to call a .NET method with the following signature:

class CustomList : System.Collections.Generic.List<string> { }

interface IProcessor { void Process(CustomList list); }

我做了一个辅助函数来生成列表：

I made a helper function to generate the list:

function ConvertTo-CustomList($obj)
{
    $list = New-Object CustomList
    if ($obj.foo) {$list.Add($obj.foo)}
    if ($obj.bar) {$list.Add($obj.bar)}
    return $list
}

然后我调用该方法：

$list = ConvertTo-CustomList(@{'foo'='1';'bar'='2'})
$processor.Process($list)

但是，调用失败，出现以下错误：

However, the call fails with the following error:

Cannot convert argument "list", with value: "System.Object[]", for "Process" to type "CustomList"
+ CategoryInfo          : NotSpecified: (:) [], MethodException
+ FullyQualifiedErrorId : MethodArgumentConversionInvalidCastArgument

因此PowerShell出于某种原因会转换为 CustomList ，其中两个项目分别指向 obje ct [] 有两个项目，无法在方法调用时将其转换回原样。如果我调用 ConvertTo-CustomList（@ {'foo'='1'}），则仅返回 string

So PowerShell by some reason converts a CustomList with two items to an object[] with two items and cannot convert it back at method call. If I call ConvertTo-CustomList(@{'foo'='1'}), just a string is returned.

我试图在此处进行强制转换，但这无济于事，函数返回后的强制转换执行失败。

I tried to put a cast here and there, but this does not help, the execution fails at the point of cast after function return.

那么如何强制 ConvertTo-CustomList 函数返回原始的 CustomList ？我不想就地初始化 CustomList ，因为在实际代码中，初始化比本例中的更为复杂。

So how can force the ConvertTo-CustomList function to return the original CustomList? I would not like to initialize the CustomList in-place because in real code the initialization is more complex than in this example.

一种可能的解决方法是使用 Add-Type Commandlet在C＃中实现辅助函数，但我希望将代码保留为单一语言。

A possible workaround is to implement the helper function in C# using the Add-Type commandlet, but I would prefer to keep my code in single language.

推荐答案

return $list

导致集合拆散并逐一吸取。这就是PowerShell的本质。

causes the collection to unravel and get "piped" out one by one. Such is the nature of PowerShell.

您可以通过使用一元数组运算符，：

You can prevent this, by wrapping the output variable itself in a 1-item array, using the unary array operator ,:

return ,$list

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