Dynamically retrieve class information in Powershell

Question

So the question is fairly simple but I'm not sure how to word it in order to find the answer.

I'm trying to access a class i.e. [MyCustomClass] in order to check static properties but I need to do it dynamically. How do I inject the class name like [$className]?

Or are there any cmdlets or .NET class functions I can use for this purpose? I tried searching Get-Command *Class* and some similar commands but am not coming up with anything.

Answer 1

There are 2 primary options for resolving a given type by name, each with slightly different behavior:

1. Using a cast to [type]:

$className = 'MyCustomClass'
$myType = [type]$className

Attempting to cast a non-existing type name will throw an exception:

PS ~> [type]'Not actually a type'
Cannot convert the "Not actually a type" value of type "System.String" to type "System.Type".
At line:1 char:1
+ [type]'Not actually a type'
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvalidCastFromStringToType

2. Using the -as type conversion operator (introduced in PowerShell version 3.0):

$myType = 'MyCustomClass' -as [type]

Unlike casting, the -as operator never throws - it simply returns $null:

PS ~> $myType = 'this does not exist' -as [type]
PS ~> $null -eq $myType
True

Common for both of these is that you can now resolve the static members of [MyCucstomClass]:

$myType::MyProperty

---

The static member operator :: also works on instance references, so if you have an object of type [MyCustomClass], use that in place of a type literal:

class MyClass
{
  static [string] $StaticValue = 'Static string value'
}

PS ~> $instance = [MyClass]::new()
PS ~> $instance::StaticValue
Static string value

Answer 2

You can use Invoke-Expression to run something you still have to build:

$class = 'DateTime'
Invoke-Expression "[$class]::Now"