How to set PowerShell OutputType for a list of named properties

Question

Consider this function which returns a table of string values, each row having two string properties with names DisplayName and DisplayVersion:

function Get-InstalledDotNetPacks{
  [CmdletBinding()]
  Param()
  Get-ItemProperty `
      -Path "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*", `
            "HKLM:\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*" |
       Where {$_.DisplayName -like '*.NET*'} |
       Select-Object DisplayName, DisplayVersion |
       Sort -Property DisplayName
}

What can I do with OutType() to reveal the two property names that the function will return?

Answer 1

Easiest way would be to define a class that serves as a property bag and allows discovery of those two properties:

class DotNetPack {
    [string] $DisplayName
    [string] $DisplayVersion
}

Then you get rid of Select-Object, cause that one returns PSCustomObject, and replace it with instances of your class instead:

function Get-InstalledDotNetPacks {
    [OutputType([DotNetPack])]
    [CmdletBinding()]
    param(
        [ValidateNotNullOrEmpty()]
        [string[]] $Path = @(
            'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*'
            'HKLM:\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*'
        )
    )

    Get-ItemProperty -Path $Path |
        Where-Object { $_.DisplayName -like '*.NET*' } |
        Sort-Object -Property DisplayName |
        ForEach-Object {
            [DotNetPack]@{
                DisplayName    = $_.DisplayName
                DisplayVersion = $_.DisplayVersion
            }
        }
}

And completion works fine after: