PowerShell: Add a function with a parameter to an object

add-function-with-param.ps1

$result | Add-Member -MemberType ScriptMethod ExpandString -Value {
    [cmdletbinding()]
    param(
        [Parameter(
            Mandatory=$true)]
        [string]
        $unexpandedValue
    )
    process{
        if($this.ProjectInstance){
            return $this.ProjectInstance.ExpandString($unexpandedValue)
        }
        else{
            'project is null'
        }
    }
}

@aaroncalderon, you have added the scriptmethod to $result but you're trying to invoke it on ProjectInstance.