Adding a property that is hidden unless it has a value

Question

I'm adding a class related to software packages. Here is a barebones version for the purposes of this question:

class Package {
    $Name; $Latest; $Prerelease
    [string]ToString(){ return $this.Name }
}
$test = [Package]::new()
$test.Name = 'Example'
$test.Latest = '0.1'

When I perform the command $test or $test | Format-Table, I want the $Prerelease property to be hidden unless it's been given a value.

And, while this next part isn't a requirement, I also want it to be exposed when something like Format-Table -Force is used.

I swear I've witnessed other objects in PowerShell behave similarly, but I haven't been able to recall what they were. If this isn't doable for an object made with pure PowerShell, I wouldn't mind something using C# via Add-Type.

P.S. In regards to suggesting an alternative, bear in mind I want quoting the object to output the $Name property as it does in the class I posted above, e.g. "$test"

Answer 1

As mentioned in the comments, this is easier achieved by simply using a [PSCustomObject] expression after conditionally adding properties to the target hashtable/dictionary.

You can then add an override for the ToString() method to the resulting object:

function New-VopelPackage {
  param(
    [Parameter(Mandatory = $true)]
    [string]$Name,

    [Parameter(Mandatory = $true)]
    [string]$Latest,

    [Parameter(Mandatory = $false)]
    [switch]$Prerelease
  )

  # Collect the mandatory properties
  $newPackageProperties = [ordered]@{
    Name = $Name
    Latest = $Latest
  }

  # Conditionally add the optional one
  if ($PSBoundParameters.ContainsKey('Prerelease')) {
    $newPackageProperties['Prerelease'] = $Prerelease.IsPresent
  }

  # Create the object
  $package = [PSCustomObject]$newPackageProperties 

  # ... and override ToString()
  $toStringMemberParams = @{
    Name       = 'ToString'
    MemberType = 'ScriptMethod'
    Value      = { return $this.Name }
    Force      = $true
    PassThru   = $true
  }

  return $package |Add-Member @toStringMemberParams
}

Now you can create package objects with the behavior described:

PS ~> $package = New-VopelPackage Example 0.1
PS ~> $package

Name    Latest
----    ------
Example 0.1

PS ~> "$package"
Example
PS ~> $prereleasePackage = New-VopelPackage Example 0.1 -Prerelease
PS ~> $prereleasePackage

Name    Latest Prerelease
----    ------ ----------
Example 0.1          True

PS ~> "$prereleasePackage"
Example