Should all [psobject] cmdlet parameters be changed to [object]? #5551
Description
From what I understand, [psobject] is an invisible helper type used behind the scenes.
However, some cmdlets do expose that type directly via their -InputObject parameters.
On a related note regarding output: When cmdlets write to the pipeline, the output objects are invariably [psobject]-wrapped:
# A number literal of type [int], for instance, is not [psobject]-wrapped
PS> 1 -is [psobject]
False
# Passing that number literal through Write-Output adds a [psobject] wrapper.
PS> (Write-Output 1) -is [psobject]
TrueThis extra [psobject] wrapper is typically benign, but on occasion does result in different behavior - see #5579.
Is there a good reason to declare parameters as [psobject] or [psobject[]] - thereby arguably leaking an implementation detail - when [object] and [object[]] should do?
Here's the list of cmdlets that have [psobject] / [psobject[]] parameters as of PowerShell Core v6.0.0-rc:
> $type = [psobject]; Get-Command -pv c | % { if ($_.Parameters) { $_.Parameters.GetEnumerator() } } | % Value | ? { $_.ParameterType -eq $type } | Select-Object @{ l='Command'; e={ $c }}, @{ l='Parameter'; e='Name'}, @{ l='Type'; e='ParameterType' }
Command Parameter Type
------- --------- ----
Format-Xml InputObject System.Management.Automation.PSObject
Get-TypeInfo InputObject System.Management.Automation.PSObject
Get-TypeName InputObject System.Management.Automation.PSObject
Write-ErrorString InputObject System.Management.Automation.PSObject
Write-StdErr InputObject System.Management.Automation.PSObject
Add-Member InputObject System.Management.Automation.PSObject
ConvertTo-Csv InputObject System.Management.Automation.PSObject
ConvertTo-Html InputObject System.Management.Automation.PSObject
ConvertTo-Xml InputObject System.Management.Automation.PSObject
Export-Clixml InputObject System.Management.Automation.PSObject
Export-Csv InputObject System.Management.Automation.PSObject
ForEach-Object InputObject System.Management.Automation.PSObject
Format-Custom InputObject System.Management.Automation.PSObject
Format-Hex InputObject System.Management.Automation.PSObject
Format-List InputObject System.Management.Automation.PSObject
Format-Table InputObject System.Management.Automation.PSObject
Format-Wide InputObject System.Management.Automation.PSObject
Get-Member InputObject System.Management.Automation.PSObject
Get-Unique InputObject System.Management.Automation.PSObject
Group-Object InputObject System.Management.Automation.PSObject
Invoke-Command InputObject System.Management.Automation.PSObject
Measure-Command InputObject System.Management.Automation.PSObject
Measure-Object InputObject System.Management.Automation.PSObject
New-Event Sender System.Management.Automation.PSObject
New-Event MessageData System.Management.Automation.PSObject
Out-Default InputObject System.Management.Automation.PSObject
Out-File InputObject System.Management.Automation.PSObject
Out-Host InputObject System.Management.Automation.PSObject
Out-Null InputObject System.Management.Automation.PSObject
Out-String InputObject System.Management.Automation.PSObject
Register-EngineEvent MessageData System.Management.Automation.PSObject
Register-ObjectEvent InputObject System.Management.Automation.PSObject
Register-ObjectEvent MessageData System.Management.Automation.PSObject
Select-Object InputObject System.Management.Automation.PSObject
Select-String InputObject System.Management.Automation.PSObject
Set-ItemProperty InputObject System.Management.Automation.PSObject
Sort-Object InputObject System.Management.Automation.PSObject
Start-Job InputObject System.Management.Automation.PSObject
Tee-Object InputObject System.Management.Automation.PSObject
Trace-Command InputObject System.Management.Automation.PSObject
Where-Object InputObject System.Management.Automation.PSObject
> $type = [psobject[]]; Get-Command -pv c | % { if ($_.Parameters) { $_.Parameters.GetEnumerator() } } | % Value | ? { $_.ParameterType -eq $type } | Select-Object @{ l='Command'; e={ $c }}, @{ l='Parameter'; e='Name'}, @{ l='Type'; e='ParameterType' }
Command Parameter Type
------- --------- ----
Add-History InputObject System.Management.Automation.PSObject[]
Compare-Object ReferenceObject System.Management.Automation.PSObject[]
Compare-Object DifferenceObject System.Management.Automation.PSObject[]
ConvertFrom-Csv InputObject System.Management.Automation.PSObject[]
New-Event EventArguments System.Management.Automation.PSObject[]
Write-Output InputObject System.Management.Automation.PSObject[]