Question

I am building an automation system using Powershell and I would like to define custom .Net types so that I can structure my application in a similar way to the other code I write.

At first, I tried using ‘Add-Type’ to import types from c# files into my application but I found this to be extremely painful to debug as a .net type can only be loaded once during per Powershell session. This means that when there are errors a single change to my code requires me to restart my app (I might as well be using C#).

At the moment I am simulating types in Powershell by using factory functions that dynamically generate PSObjects with the semantics I need. This does work but it is very verbose and I don’t seem to be able to declare private variables or methods for encapsulation.

Is there an easier way to achieve what I want?

If not….

Am I somehow barking up the wrong tree by wanting to write my Powershell code using abstract data types?

Is there a better way to structure my system that I should know about?

Can I achieve some encapsulation with what I am doing now?

Answer 1

1) I haven’t tried it, but this project looks promising: PSClass – Object Oriented Scripting in Powershell. Some features it offers:

PsClass is currently implemented in
Powershell in a single file. Makes it
simple to use. It supports the
following OO concepts.

• Inheritance
• Polymorphism
• Encapsulation
• Constructors with parameters
• Notes – read-write variables
• Methods – scriptblocks
• Properties with Get scriptblocks and optional Set scriptblocks
• Static and Private Notes and Methods

2) You could use custom modules like this:

$o = New-Module -AsCustomObject -Function GetVar, AddToVar {
    $script:var = 1
    function checkRange { if ($var -gt 3 -or $var -lt 0) { throw 'not in range <0,3>' } }
    function GetVar { $script:var }
    function AddToVar { param($add) checkRange; $script:var += $add; $script:var }
}
$o.GetVar()
$o.AddToVar(2)
$o.AddToVar(1)
$o.GetVar()
$o.checkRange()
$o | gm

Try to copy it to your ide/console and run it. $script:var is private member that can be used only from functions GetVar,AddToVar. checkRange is private as well.

---

Personally I wouldn’t use PowerShell for such a task if I needed real OOP (available in C#). PowerShell has some support for objects, but very poor for OOP.