Array and array member methods

Question

The following PowerShell code:

class MyClass { }
class MyClass1 : MyClass {
    [void] OutMsg([string] $Str) {
        Write-Host -Object "MyClass1: $Str"
    }
}
class MyClass2 : MyClass {
    [void] OutMsg([string] $Str) {
        Write-Host -Object "MyClass2: $Str"
    }
}
[MyClass[]] $ClassArray = @([MyClass1]::new(), [MyClass2]::new())
$ClassArray.OutMsg('TestString')

outputs:

MyClass1: TestString
MyClass2: TestString

Calling

Get-Member -InputObject $ClassArray

shows me that the array object itself has no OutMsg method.

Why can I call $ClassArray.OutMsg('') though (looks like this calls the OutMsg method of each array member in turn)?

Mureinik · Accepted Answer · 2025-07-02 11:03:34Z

5

That is actually a well defined behavior of arrays in PowerShell.

To quote the documentation:

Starting in PowerShell 3.0, when you use the member-access operator to access a member that doesn't exist on a list collection, PowerShell automatically enumerates the items in the collection and attempts to access the specified member on each item.

You can find additional details in the about member-access enumeration page.

answered Jul 2 at 11:03

Mureinik

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