Transformation class example

Test-TransformationClasses.ps1

# transformation class that transforms string to service controller object
class ServiceSingleTransformation : System.Management.Automation.ArgumentTransformationAttribute {

    [object] Transform([System.Management.Automation.EngineIntrinsics]$EngineIntrinsics, [object] $InputData) {
        $item = $InputData
        if ($item -is [string]) {
            $item = Get-Service -name "$item"
        }elseif ($item -is [System.ServiceProcess.ServiceController]) {
            $item = $item
        }else {
            throw "Invalid type"
        }
        return ($item)
    }
}

function Test-TransformationClasses {
#add comment based help
<#
.SYNOPSIS
    This function demonstrates how transformation classes work
.DESCRIPTION
    This function demonstrates how transformation classes work
.PARAMETER Service
    This is the service you want to query
.EXAMPLE
    Test-TransformationClasses -Service "w32time"
.EXAMPLE
    Test-TransformationClasses -Service (Get-Service -name "w32time")
#>
    [CmdletBinding()]

    Param (
        # Param1 help description
        [Parameter()]
        [ServiceSingleTransformation()]
        [System.ServiceProcess.ServiceController]
        $Service

    )

    begin {}

    process {
        # returns service as System.ServiceProcess.ServiceController
        $Service

        # throws an error because transformation class only accepts string or System.ServiceProcess.ServiceController
        # every time you assign $service a value the transformation class is called
        $Service = $null
    }

    end {}
}