如何动态设置 PowerShell 变量的类型? [英] How do I dynamically set the type of PowerShell variables?

问题描述

是否可以从字符串中获取 System.Type，然后将其应用于变量?

以下是我尝试转换以使其更安全的函数(即不涉及调用字符串):

函数 ParseLine($Type, $VariableName, $Value){调用表达式[$Type] `$$VariableName = $Value"}

我查看了New-Variable和Set-Variable，但定义中没有与类型设置相关的参数.

我希望得到如下所示的内容，但我找不到参数 Type 或等效参数:

函数 ParseLine($Type, $VariableName, $Value){新变量 -Name $VariableName -Value $Value -Type ([type] $Type)}

上下文:我正在尝试创建一个简单的解析器定义，如下所示:

$ResponseLogFormat = New-InputFormat {ParseLine -Type int -VariableName RecordLengthRepeatedSection -RepeatCount $RecordLength {ParseLine 字符串 +ComputerNameParseLine double +AverageResponse}}$ResponseLogFormat.Parse( $FilePath )

解决方案

您可以使用 -as 运算符将变量转换为特定类型:

函数 ParseLine($Type, $VariableName, $Value){Set-Variable $VariableName -Scope 1 -Value ($Value -as ($Type -as [type]))}

这将使用 -as 从 $Type 字符串创建一个类型，然后使用它来转换 $Value.

我不确定你对这个变量的意图，但是如果你想在函数完成后持久化它，你需要在父作用域中设置它.

Is it possible to get a System.Type from a string and then apply it to a variable?

The following is the function that I tried to convert to make it safer (i.e. not involve invoking a string):

Function ParseLine($Type, $VariableName, $Value){
    Invoke-Expression "[$Type] `$$VariableName = $Value"
}

I looked at New-Variable and Set-Variable, but there is no type-setting-related parameter in the definition.

I expected something that looks like below, but I couldn't find the parameter Type or equivalent:

Function ParseLine($Type, $VariableName, $Value){
    New-Variable -Name $VariableName -Value $Value -Type ([type] $Type)
}

Context: I am experimenting to create a simple parser definition that looks like:

$ResponseLogFormat = New-InputFormat {
    ParseLine -Type int -VariableName RecordLength
    RepeatedSection -RepeatCount $RecordLength {
        ParseLine string +ComputerName
        ParseLine double +AverageResponse
    }
}

$ResponseLogFormat.Parse( $FilePath )

解决方案

You can cast variables to a specific type using the -as operator:

Function ParseLine($Type, $VariableName, $Value){
    Set-Variable $VariableName -Scope 1 -Value ($Value -as ($Type -as [type]))
}

That will use -as to create a type from the $Type string, and then use that to cast $Value.

I am not sure of your intent with the variable, but if you want to persist it after the function is finished, you need to set it in the parent scope.

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