Strange behavior in PowerShell function returning DataSet/DataTable

Question

This is driving me crazy. I have a library I source from multiple scripts, which contains the following function:

function lib_open_dataset([string] $sql) {
         


        

Answer 1

PowerShell special-cases the DataTable internally. It does not implement any of the usual suspect interfaces like ICollection, IList or IEnumerable which normally trigger the unrolling. You can dig into this a bit with:

PS> $dt = new-object data.datatable
PS> $dt -is [collections.ienumerable]
False

Yet:

PS> $e = [management.automation.languageprimitives]::GetEnumerator($dt)
PS> $e.gettype()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
False    False    RBTreeEnumerator                         System.ValueType

-Oisin