Powershell Call Base Class Function From Overidden Function

Question

I want to make a call to the parent function from its overidden function, i isolated my problem in the following code:

class SomeClass{
  [type]GetType(){
    write-host 'hooked'
    return $BaseClass.GetType() # how do i call the BaseClass GetType function??
  }
}
SomeClass::new().GetType()

i am expecting an output like this:

hooked
IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     SomeClass                                System.Object

Object.GetType() is non-virtual and cannot be overridden (although you can hide it in various ways). What exactly are you trying to accomplish? — Mathias R. Jessen
– Mathias R. Jessen, Commented Mar 11, 2022 at 14:42

mklement0 · Accepted Answer · 2023-01-03 18:42:19Z

In oder to call a method on the base class, cast $this to it (([object] $this).GetType(), in your case, given that your class implicitly derives from [object](System.Object)):

class SomeClass  {
  [type]GetType(){
    Write-Verbose -Verbose hooked!
    # Casting to [object] calls the original .GetType() method.
    return ([object] $this).GetType()
  }
}

[SomeClass]::new().GetType()

As an aside re referring to the base class in PowerShell custom classes:

PowerShell only allows you to reference the base class via the abstract base identifier in base-class constructor calls:

class Foo { [int] $Num; Foo([int] $Num) { $this.Num = $Num } }
class FooSub : Foo { FooSub() : base(42) { } } # Note the `: base(...)` part
[FooSub]::new().Num # -> 42

In methods, the only (non-reflection-based) way to refer to the base class is via a type literal (cast), which in essence requires you to hard-code the base-class name (as also shown with ([object] $this) above):

class Foo { [string] Method() { return 'hi' } }
# Note the need to name the base class explicitly, as [Foo].
class FooSub : Foo { [string] Method() { return ([Foo] $this).Method() + '!' } }
[FooSub]::new().Method() # -> 'hi!'

Caveat: There appears to be a bug in Windows PowerShell (no longer present in PowerShell (Core) 7+), where calling a base class' method fails if the base class is a generic type that is constructed with type argument [pscustomobject] aka [psobject]. Use a reflection-based workaround in that case; e.g.:

class Foo : System.Collections.ObjectModel.Collection[pscustomobject] {
  [void] Add([pscustomobject] $item) {
    Write-Verbose -Verbose hooked!
    # Use reflection to call the base class' .Add() method.
    # Note: In *PowerShell Core*, this workaround isn't necessary, and the usual would work:
    #         ([System.Collections.ObjectModel.Collection[pscustomobject]] $this).Add($item)
    # Note the use of .GetMethod() and .Invoke()
    [System.Collections.ObjectModel.Collection[pscustomobject]].GetMethod('Add').Invoke($this, [object[]] $item)
  }
}

Would it be worthwhile to add in the GetMethod of the base type from your answer here?

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