# Create a [System.Management.Automation.PSCustomObject]
# Note that you cannot create a System.Management.Automation.PSCustomObject
# instance with `New-Object System.Management.Automation.PSCustomObject ...`.
# [pscustomobject] is actually [psobject] ([System.Management.Automation.PSObject])
$co = [pscustomobject] @{ foo = 'bar' }

$co.GetType().FullName

'---'

# This should be and is $True.
# Note that using `-is [pscustomobject]` is NOT equivalent and while it also returns $True,
# it does so for any object that has an (invisible) extra [psobject] wrapper, due to the identity
# of [pscustomobject] and [psobject]. All objects returned from *cmdlets* have that extra
# wrapper; e.g., `(Get-Item /) -is [pscustomobject]` yields $True also, while the seemingly
# equivalent  `[System.IO.DirectoryInfo]::new('/') -is [pscustomobject]`  doesn't - see #5579
$co -is [System.Management.Automation.PSCustomObject]

'---'

# The $co -as ... expression should effectively pass $co through, but doesn't.
# Note that using `-as [pscustomobject]` is NOT equivalent - and pointless, because 
# it passes *any* object through, given that it is the same as `-as [psobject]`, which  is what ALL 
# objects in PowerShell are (semi-secretly) wrapped in.
$null -ne ($co -as [System.Management.Automation.PSCustomObject])

PowerShell Core v6.0.0-beta.4 on macOS 10.12.5
PowerShell Core v6.0.0-beta.4 on Ubuntu 16.04.2 LTS
PowerShell Core v6.0.0-beta.4 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)
Windows PowerShell v5.1.15063.413 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)