使用存储在变量中的类型进行PowerShell类型转换 [英] PowerShell type cast using type stored in variable

问题描述

我想将.NET对象转换为其他.NET类型，但是：

• 目标.NET类型（类）存储在变量中


• 我不想使用 -as PowerShell运算符


• 我使用的是复杂的非原始类型

您将如何实现？

例如，这是 PowerShell方法，但我不想使用 -as ：

  $ TargetType = [System.String]; ＃我要转换为
 1的类型-as $ TargetType; ＃将对象强制转换为$ TargetType 
  

不幸的是，这不起作用：

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

..因为在这种情况下PowerShell不允许在方括号内使用变量。 / p>

我在想类似的东西：

  $ TargetType = [系统。串]; 
 $ TargetType.Cast（1）; ＃.NET框架中是否存在类似的内容？ 
  

可以使用.NET方法语法吗？

解决方案

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?

解决方案

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()

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