$this object reference for nested custom objects in Powershell - powershell

Question

There's something that I can't quite seem to wrap my head around when trying to do object references in Powershell. Not sure if there's something that I am missing out on.
A sample code illustrating this problem is as follows:
function Create-Custom-Object {
$oResult = New-Object -TypeName PSObject -Property (#{
"Test" = $(Get-Date);
})
Add-Member -memberType ScriptMethod -InputObject $oResult -Name "GetTest" -Value {
return $this.Test;
}
return $oResult
}
function Create-Wrapper-Object {
$oObject = $(Create-Custom-Object)
$oResult = New-Object -TypeName PSObject -Property (#{
"Object" = $oObject;
"Test" = $(Get-Date);
})
Add-Member -MemberType ScriptMethod -InputObject $oResult -Name "WrapTest" -Value {
return $this.Object.GetTest()
}
return $oResult
}
$oCustom = Create-Custom-Object
sleep 5
$oWrapper = Create-Wrapper-Object
echo "Custom-Test: $($oCustom.Test)"
echo "Wrapper-Test: $($oWrapper.Test)"
echo "GetTest: $($oCustom.GetTest())"
echo "WrapTest: $($oWrapper.WrapTest())"
When run, the output is as per below:
>powershell -file test.ps1
Custom-Test: 11/20/2017 16:10:19
Wrapper-Test: 11/20/2017 16:10:24
GetTest: 11/20/2017 16:10:19
WrapTest: 11/20/2017 16:10:24
What puzzled me is that the call to WrapTest() on the wrapper object returns the "Test" attribute value from the wrapper object instead of the embedded custom object. Why is Powershell behaving like this?

Answer 1

I suspect that the problem here (based on the assumed intent of the sleep 5) is that $oCustom is assigned a Custom-Object and then 5 seconds later $oWrapper is assigned a Wrapper-Object which contains a new Custom-Object with essentially the same [DateTime] value (to the nearest second), not the (intended?) previously created $oCustom. WrapTest() is not returning the Test member of $oWrapper but the indistinguishable Test member of its own Custom-Object in $oWrapper.Object. In order to create a (generic) wrapper object, you need something to wrap, otherwise it's really just a (specific) nested object. Something like this:
function Create-Wrapper-Object {
param ($ObjectToWrap)
$oResult = New-Object -TypeName PSObject -Property (#{
"Object" = $ObjectToWrap; # presumably with a GetTest() method
"Test" = $(Get-Date); # remember the time of wrapping
})
Add-Member -MemberType ScriptMethod -InputObject $oResult -Name "WrapTest" -Value {
return $this.Object.GetTest()
}
return $oResult
}
With the (assumed to be) desired result:
$oCustom = Create-Custom-Object
sleep 5
$oWrapper = Create-Wrapper-Object $oCustom
echo "Custom-Test: $($oCustom.Test)"
Custom-Test: 05/31/2021 08:52:30
echo "Wrapper-Test: $($oWrapper.Test)"
Wrapper-Test: 05/31/2021 08:52:35
echo "GetTest: $($oCustom.GetTest())"
GetTest: 05/31/2021 08:52:30
echo "WrapTest: $($oWrapper.WrapTest())"
WrapTest: 05/31/2021 08:52:30