LINQ 可以在 PowerShell 中使用吗? [英] Can LINQ be used in PowerShell?

问题描述

我正在尝试在 PowerShell 中使用 LINQ.看起来这应该是完全可能的，因为 PowerShell 是建立在 .NET Framework 之上的，但我无法让它工作.例如，当我尝试以下(人为的)代码时:

$data = 0..10[System.Linq.Enumerable]::Where($data, { param($x) $x -gt 5 })

我收到以下错误:

<块引用>

找不到Where"和参数计数的重载:2".

没关系，这可以通过 Where-Object 来完成.这个问题的重点不是要找到在 PowerShell 中执行此操作的惯用方法.如果我可以使用 LINQ，那么在 PowerShell 中完成某些任务会轻松数光年.

解决方案

您的代码的问题是 PowerShell 无法决定 ScriptBlock 实例 ({ ...}) 应该被强制转换.因此，它无法为 Where 方法.而且它也没有明确指定泛型参数的语法.要解决此问题，您需要自己将 ScriptBlock 实例强制转换为正确的委托类型:

$data = 0..10[System.Linq.Enumerable]::Where($data, [Func[object,bool]]{ param($x) $x -gt 5 })

<块引用>

为什么 [Func[object, bool]] 有效，而 [Func[int, bool]] 无效?

因为您的 $data 是 [object[]]，而不是 [int[]]，因为 PowerShell 创建了 [object[]] 默认为数组；但是，您可以显式构造 [int[]] 实例:

$intdata = [int[]]$data[System.Linq.Enumerable]::Where($intdata, [Func[int,bool]]{ param($x) $x -gt 5 })

I am trying to use LINQ in PowerShell. It seems like this should be entirely possible since PowerShell is built on top of the .NET Framework, but I cannot get it to work. For example, when I try the following (contrived) code:

$data = 0..10

[System.Linq.Enumerable]::Where($data, { param($x) $x -gt 5 })

I get the following error:

Cannot find an overload for "Where" and the argument count: "2".

Never mind the fact that this could be accomplished with Where-Object. The point of this question is not to find an idiomatic way of doing this one operation in PowerShell. Some tasks would be light-years easier to do in PowerShell if I could use LINQ.

解决方案

The problem with your code is that PowerShell cannot decide to which specific delegate type the ScriptBlock instance ({ ... }) should be cast. So it isn't able to choose a type-concrete delegate instantiation for the generic 2nd parameter of the Where method. And it also does't have syntax to specify a generic parameter explicitly. To resolve this problem, you need to cast the ScriptBlock instance to the right delegate type yourself:

$data = 0..10
[System.Linq.Enumerable]::Where($data, [Func[object,bool]]{ param($x) $x -gt 5 })

Why does [Func[object, bool]] work, but [Func[int, bool]] does not?

Because your $data is [object[]], not [int[]], given that PowerShell creates [object[]] arrays by default; you can, however, construct [int[]] instances explicitly:

$intdata = [int[]]$data
[System.Linq.Enumerable]::Where($intdata, [Func[int,bool]]{ param($x) $x -gt 5 })

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