Hi /r/powershell,

I came across a behavior that I can't explain. I think it has something to do with referencial variables, but I'm not sure. I tried to narrow it down to a simple example, and I hope I can explain it. I am very confused ...

Let's say I have a refernce object. I compare it to a difference object using a function. In that function I copy the values from the reference object to the difference object, and output a new custom object that contains both objects.

Function New-ReferenceObject {
    Param (
        [String]$value1,
        [String]$value2
    )

    [PsCustomObject] @{
        'Prop1' = $value1
        'Prop2' = $value2
    }

}

Function New-DifferenceObject {
    Param (
        [String]$value1
    )

    [PsCustomObject] @{
        'Prop1' = $null
        'Prop2' = $null
        'Prop3' = $value1
    }

}

Function New-Evaluation{
    Param (
        [PsCustomObject]$Reference,
        [PsCustomObject]$Difference
    )

    $Difference.Prop1 = $Reference.Prop1
    $Difference.Prop2 = $Reference.Prop2

    [PsCustomObject] @{
        'Reference' = $Reference
        'Evaluated' = $Difference
    }

}

So I create two objects $Reference1 and $Difference ...

$Reference1 = New-ReferenceObject -value1 5 -value2 10 
$Difference = New-DifferenceObject -value1 5

PS C:\Windows\system32> $Reference1

Prop1 Prop2
----- -----
5     10   

PS C:\Windows\system32> $Difference

Prop1 Prop2 Prop3
----- ----- -----
            5    

and save the output of the evaluation in Evaluated1:

$Evaluated1 = New-Evaluation-Reference $Reference1 -Difference $Difference

PS C:\Windows\system32> $Evaluated1

Reference            Evaluated                    
---------            ---------                    
@{Prop1=5; Prop2=10} @{Prop1=5; Prop2=10; Prop3=5}

So far, everything is as expected. However, if I create a second reference object, evaluate it against the same difference object, and store it in $Evaluated2, the content of $Evaluated1 is changed:

$Reference2 = New-ReferenceObject -value1 20 -value2 30

PS C:\Windows\system32> $Reference2 

Prop1 Prop2
----- -----
20    30   

$Evaluated2 = New-Evaluation-Reference $Reference2 -Difference $Difference

PS C:\Windows\system32> $Evaluated1 

Reference            Evaluated                     
---------            ---------                     
@{Prop1=5; Prop2=10} @{Prop1=20; Prop2=30; Prop3=5} 

The Evaluated property of $Evaluated1 now contains the values of $Reference2, although I never altered it.

What is going on here?