New-Object vs [type]::New(), script vs ISE

Question

Sigh. Another day, another PowerShell method interaction with .NET I just don't understand. This time with signed XML, but it's an issue with how to create a new object.

$signedXml = New-Object system.security.cryptography.xml.signedXml -argumentList:$xml works. But where possible I have been moving to [type]::New(). And... $signedXml = [System.Security.Cryptography.Xml.SignedXml]::New($xml) doesn't work. In a script. Works fine in the ISE, but when run as a script I get

Unable to find type [System.Security.Cryptography.Xml.SignedXml].

So, what is going on under the hood such that using a constructor only works in the ISE, while New-Object works in a script also. And, how does one grok what is going to fail? I have plenty of other things I have moved to [type]::New() with no issues. Is my only option to fall back on the commandlet when the constructor fails me? That results in less consistent, readable code in my view.

Answer 1

Try:

Using namespace System.Security.Cryptography.Xml;

Powershell has the ability to call namespaces like C#.

The below code seemed to work with for me fine in Powershell Core:

Using namespace System.Security.Cryptography.Xml;

$xml = [xml]::New()
$signed = [SignedXml]::New($xml)

Answer 2

It didn't work for me in the ISE either, until I did this. Maybe you loaded some module in the ISE that did something like it.

using assembly system.security