Unary comma.

Have you ever had a problem that you wanted to do something with a collection as a whole and you couldn’t? I had this issue several times. Most obvious and most common problem is discovering collection properties. Is there a length property on the collection? Let’s see:

PowerShell, using GeSHi 1.0.8.8

1. (1,2,3,4) | gm -MemberType Property

It returns literally nothing. Why? Because PowerShell assumes you want to get member of elements rather than whole collection. So what should you do? Use unary comma:

PowerShell, using GeSHi 1.0.8.8

1. ,(1,2,3,4) | gm -MemberType Property
4. TypeName: System.Object[]
6. Name           MemberType Definition
7. —- ———- ———-
8. IsFixedSize    Property   System.Boolean IsFixedSize {get;}
9. IsReadOnly     Property   System.Boolean IsReadOnly {get;}
10. IsSynchronized Property   System.Boolean IsSynchronized {get;}
11. Length         Property   System.Int32 Length {get;}
12. LongLength     Property   System.Int64 LongLength {get;}
13. Rank           Property   System.Int32 Rank {get;}
14. SyncRoot       Property   System.Object SyncRoot {get;}

I had problem with that when I was completing my Inventory module. In this module I create two collection types: one is build on top of System.Collections.Hashtable and second is based on System.Collections.ArrayList. I’ve created functions within module to return both types. It was quite easy with hashtable:

PowerShell, using GeSHi 1.0.8.8

1. Import-Csv $Path | ForEach-Object -Begin {
2. $InventoryHash = New-Object PXL.Hash
3. Write-Host -ForegroundColor Yellow “Processing file: $Path”
4. } -Process {
5. $InventoryHash.Add($_.Name,$(New-Object PXL.PC -Property @{
6. Name=$_.Name
7. SN=$_.SN
8. User=$_.User
9. Last=$_.Last
10. Model=$_.Model
11. SP=$_.SP
12. Batt=$_.Batt
13. MAC = $_.MAC
14. tel = $_.tel
15. InvDate=$_.InvDate
16. PhysicalMemory=$([double]($_.RAM -replace ‘ GB’) * 1GB)
17. FreeSpace=$([double]($_.Free -replace ‘ GB’) * 1GB)
18. HDsize=$([double]($_.HD -replace ‘ GB’) * 1GB)
19. })
20. ) | Out-Null
21. } -end {
22. Write-Host -ForegroundColor Cyan ‘Done!’
23. $InventoryHash
24. }

With PXL.List I had to use unary comma, otherwise it would return System.Object[] – and that would not contain any of ScriptMethods I had prepared for my type.

PowerShell, using GeSHi 1.0.8.8

1. # return object without unary comma….
2. -end {
3. Write-Host -ForegroundColor Cyan ‘Done!’
4. $InventoryList
5. }
7. $inv = Import–InventoryList
8. Processing file: A:\Inventory\Full.csv
9. Done!
10. $inv.GetType().FullName
11. System.Object[]
13. # same object, this time using unary comma
15. -end {
16. Write-Host -ForegroundColor Cyan ‘Done!’
17. ,$InventoryList
18. }
21. $inv = Import–InventoryList
22. Processing file: A:\Inventory\Full.csv
23. Done!
24. $inv.GetType().FullName
25. PXL.List

Object preserved, methods there were I need them – all happy. 🙂 All thanks to unary comma. So if you are fighting with collection and banging your head against the desk – what I did wrong – maybe unary comma is all you need to move on. 🙂