Introduction

Yesterday at the gym I was listening to the PModem show of the PowerScripting Podcast and suddenly I noticed that I rolled my own version of the Select-Object cmdlet for a blog post that I published a few days ago: Using Partial Clones for TDD and Polymorphism in PowerShell. In this blog post I replace my version of cloning selected properties with the Select-Object cmdlet.

Figure 1: Never roll your own roller coaster

Changes

Figure 2: This screenshot shows the diff report generated with Winmerge

New Version

Here is the new version of the script that uses the Select-Object cmdlet

set-debugmode

function Clone-AsStub()
{
    [CmdletBinding(DefaultParameterSetName="Full")]
    param
    (
        [Parameter(Position=0, Mandatory=$true, ValueFromPipeline=$true)]
        [ValidateNotNull()]
        [PSObject] $ObjectToClone,

        [Parameter(Position=1, Mandatory=$false, ValueFromPipeline=$false)]
        [ValidateNotNullOrEmpty()]
        [string[]] $PropertiesToClone,
        
        [Parameter(Position=2, Mandatory=$false, ValueFromPipeline=$false)]
        [switch] $PreserveTypeInfo,
        
        [Parameter(Position=3, Mandatory=$false, ValueFromPipeline=$false, ParameterSetName="Magic")]
        [ValidateNotNull()]
        [ScriptBlock] $RevertScriptBlock

    )
    process
    {

        $Clone = $ObjectToClone | Select-Object -Property $PropertiesToClone
        
        if($PreserveTypeInfo)
        {
            $Clone = Add-Member -InputObject $Clone -MemberType "NoteProperty" -Name "TypeName" -Value $ObjectToClone.GetType().FullName -PassThru
        }
        
        if( $PsCmdlet.ParameterSetName -eq "Magic")
        {
            $Clone = Add-Member -InputObject $Clone -MemberType "ScriptMethod" -Name "Revert" -Value $RevertScriptBlock -PassThru
        }
        return $Clone
    }
}

Download

The new version of the script can be downloaded here: NewVersionWithSelectObject.zip

Ausblick

Rolling your own version of Select-Object is a good exercise, but at the end I would rather use Select-Object in production.