I was debugging why a powershell script started failing and it looked like it was using Hashset without referencing the System.Core assembly, so the fix is to end up with something like this:
Add-Type -AssemblyName System.Core
$hash = new-object 'System.Collections.Generic.HashSet[string]'
What I can't figure out is how it was working before, and still runs just fine on some machines, without the add-type line. What am I missing here?
To continue from David's thought, and because code in comments is horrid, you should check to see if the assembly is loaded. A small blog about checking assemblies is here
If (!(([appdomain]::currentdomain.GetAssemblies()).FullName -match "System\.Core")){
Add-Type -AssemblyName System.Core
}
$hash = new-object 'System.Collections.Generic.HashSet[string]'
I have this assembly loaded by default. Curious what the affected systems have. What is the Dot.Net framework versions on affected machines? I had some of my 3.5 code stop working after Windows updates and need to reinstall framework.
Comment from Jeroen Mostert
If you want to be really precise about it, you should verify you've got .NET's very own
System.Core, not any old impostor, and then there is no need to check that's already happened.Add-Type -AssemblyName "System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
System.Core, not any old impostor, and then there is no need to check that's already happened. Add-Type -AssemblyName "System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" on its own is enough (version policies will take care of loading a later version if necessary).
System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 not sure which one the op needs. Thanks. I'm still not sure if I should just delete this or not.HashSet exists in 3.5, I'd go with that to maximize the chance of the script running. Unless you specifically need .NET 4.0, of course, but then that won't be because of HashSet.
System.Core, Version=4.0.0.0, ... loaded -- and that assembly should load automatically if you have PowerShell 4.0, AFAIK -- then Add-Type will fail: "The type name and namespace must be unique within a session. You cannot unload a type or change it. If you need to change the code for a type, you must change the name or start a new Windows PowerShell session. Otherwise, the command fails." (See -Name parameter)Add-Type does not fail at all when attempting to load version 3.5 of System.Core is version 4.0 is already loaded (Powershell 3.0). This makes sense, since asking for 3.5 on .NET 4.0 will just get you 4.0, courtesy of versioning policy.