且构网

分享程序员开发的那些事...
且构网 - 分享程序员编程开发的那些事

使用存储在变量中的类型进行PowerShell类型转换

更新时间:2023-11-29 09:56:04

您可以使用以下方法粗略地模拟类型转换:

  [System.Management.Automation.LanguagePrimitives] :: ConvertTo($ Value,$ TargetType)

对于提供自己转换的动态对象,真正的强制转换的行为可能不同于上述方法。否则,我唯一能想到的其他区别就是性能-由于ConvertTo静态方法不提供优化,因此真正的转换可能会更好。



精确地模拟转换,您将需要生成类似以下内容的脚本块:

  function GenerateCastScriptBlock 
{
param ([type] $ Type)

[scriptblock] :: Create('param($ Value)[{0}] $ Value'-f
[Microsoft.PowerShell.ToStringCodeMethods]: :Type($ Type))
}

然后可以将此脚本块分配给函数或直接调用它,例如:

 (&(GenerateCastScriptBlock([int])) 42)。GetType( )


I'd like to cast a .NET object to another .NET type, but:

  • The target .NET type (class) is stored in a variable
  • I don't want to use the -as PowerShell operator
  • I am using complex, non-primitive types

How would you achieve this?

For example, this is the "PowerShell" way to do it, but I don't want to use -as:

$TargetType = [System.String]; # The type I want to cast to
1 -as $TargetType;             # Cast object as $TargetType

Unfortunately, this does not work:

$TargetType = [System.String];
[$TargetType]1;

.. because PowerShell does not allow the use of variables inside the square brackets, in this scenario.

I am imagining something like:

$TargetType = [System.String];
$TargetType.Cast(1); # Does something like this exist in the .NET framework?

Can it be done with .NET method syntax? Is there a static method that does this?

You can roughly emulate a cast using the following method:

[System.Management.Automation.LanguagePrimitives]::ConvertTo($Value, $TargetType)

A true cast may behave differently than the above method for dynamic objects that provide their own conversions. Otherwise, the only other difference I can think of is performance - a true cast may perform better because of optimizations not available in the ConvertTo static method.

To precisely emulate a cast, you'll need to generate a script block with something like:

function GenerateCastScriptBlock
{
    param([type]$Type)

    [scriptblock]::Create('param($Value) [{0}]$Value' -f
        [Microsoft.PowerShell.ToStringCodeMethods]::Type($Type))
}

You can then assign this script block to a function or invoke it directly, e.g.:

(& (GenerateCastScriptBlock ([int])) "42").GetType()