VBscript Public Property Set/Get equivalent in PowerShell

Question

I'm trying to add elements to a Powershell variable with Add-Member. I have no problem adding static properties with NoteProperty, and methods with ScriptMethod, like that :

$variable = New-Object PSObject
$variable | Add-Member NoteProperty Key "Value"
$variable | Add-Member ScriptMethod DoSomething { // code }

Now I'm stuck on this :

I want to add a property that has a getter and a setter and does a bunch of things via code block.

The VBScript equivalent would be this :

Class MyClass
  Public Property Get Item(name)
    // Code to return the value of Item "name"
  End Property
  Public Property Let Item(name,value)
    // Code to set the value of Item "name" to value "value"
  End Property
End Class

Note that the code sections I need to write do more than just set/get the value, they're more complex than that (set other related variables, access external data, etc...).

I failed to find anything this easy in PowerShell and ended up adding instead 2 scriptmethods, GetItem and SetItem.

What would be the best way to implement this get/let functionnality in a member of a PSObject in PowerShell ?

Thanks in advance

Answer 1

You should add -MemberType ScriptProperty and use -Value and -SecondValue:

# Make an object with the script property MyProperty
$variable = New-Object PSObject

# “internal” value holder
$variable | Add-Member -MemberType NoteProperty _MyProperty -Value 42

# get/set methods
$get = {
    Write-Host "Getting..."
    $this._MyProperty
}
$set = {
    Write-Host "Setting..."
    $this._MyProperty = $args[0]
}

# the script property
$variable | Add-Member -MemberType ScriptProperty MyProperty -Value $get -SecondValue $set

Test:

Write-Host "Original value: $($variable.MyProperty)"
$variable.MyProperty = 123
Write-Host "After assignment: $($variable.MyProperty)"

It prints:

Getting...
Original value: 42
Setting...
Getting...
After assignment: 123

Unfortunately I do not know how to make “protected/private” internal value holders like the note property _MyProperty in our example (or whether it is possible at all).

UPDATE: Apparently it’s the answer to what more or less the title asks. But the question is in fact about parameterized property, not just get/set methods implemented via script blocks. My attempt to use this type of property (ParameterizedProperty) with Add-Member has failed, perhaps it is not yet supported.