"Could not construct Closed Type using the provided arguments" error creating a generic list in Powershell

Question

I have a Powershell script where I would like to create a generic List of a type that is defined in a custom (C++/CLI) assembly.

If I run new-object My.Namespace.MyClass, I can create objects all day. However, if I run new-genericobject System.Collections.Generic.List -Of My.Namespace.MyClass, I get the below error:

New-GenericObject : Could not construct Closed Type using the provided arguments.
At line:1 char:18
+ new-genericobject <<<<  System.Collections.Generic.List -Of My.Namespace.MyClass
    + CategoryInfo          : NotSpecified: (:) [New-GenericObject], ArgumentException
    + FullyQualifiedErrorId : System.ArgumentException,Pscx.Commands.NewGenericObjectCommand

I can create lists of strings, so the basic functionality of new-genericobject is fine. Does anyone have ideas on what this error means and how it can be resolved?

x0n · Accepted Answer · 2011-11-04 15:40:02Z

2

Can you try this instead:

$list = new-object 'collections.generic.list[my.namespace.myclass]'

btw, what version of powershell are you using? what operating system?

Update

This might be a long running bug where if the element type is in a third party assembly and the collection is not in the same assembly, you must fully qualify the element type. Try this:

$list = new-object ("collections.generic.list[[{0}]]" `
    -f [MyClass].AssemblyQualifiedName)

edited Nov 4, 2011 at 15:40

answered Nov 4, 2011 at 3:26

x0n

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3 Comments

zdv Over a year ago

That results in the below error:

New-Object : Cannot find type [system.collections.generic.list[My.Namespace.MyClass]]: make sure the assembly containing this type is loaded.     At line:1 char:11     + new-object <<<<  'system.collections.generic.list[My.Namespace.MyClass]'         + CategoryInfo          : InvalidType: (:) [New-Object], PSArgumentException         + FullyQualifiedErrorId : TypeNotFound,Microsoft.PowerShell.Commands.NewObjectCommand

This is using Powershell version 2.0 on WinXP SP3.

x0n Over a year ago

Ah, I think this is a long existing bug in powershell where if the element type is in a different assembly than the collection and it is not part of the BCL, you must use a fully qualified type name. I've updated the answer.

zdv Over a year ago

Hmm, I can't seem to get that to work no matter what. I tried several variations of that approach (your approach, using it without the formatted string, etc) and I always get the above error about making sure the assembly is loaded. After doing some Googling, I found the below approach which does work but is rather verbose:

function CreateGenericList {     $dummy = New-Object My.Namespace.MyClass     $generic = [System.Collections.Generic.List``1]     $gt = $base.MakeGenericType(@($dummy.GetType()))     ,[Activator]::CreateInstance($gt) }

zdv · Accepted Answer · 2011-11-22 00:47:44Z

1

I don't really like this solution, but it is the only thing I've found to work:

function CreateGenericList
{
    $dummy = New-Object My.Namespace.MyClass
    $generic = [System.Collections.Generic.List``1]
    $gt = $generic.MakeGenericType(@($dummy.GetType()))
    ,[Activator]::CreateInstance($gt)
}

answered Nov 22, 2011 at 0:47

zdv

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