powershell - Difference between PSObject, Hashtable, and PSCustomObject

Question

Can anybody explain the details? If I create an object using

$var = [PSObject]@{a=1;b=2;c=3}

and then I look for its type using getType() PowerShell tells me it's of type Hashtable.

When using Get-Member (alias gm) to inspect the object it's obvious that a hashtable has been created, since it has a keys and a values property. So what's the difference to a "normal" hashtable?

Also, what's the advantage of using a PSCustomObject? When creating one using something like this

$var = [PSCustomObject]@{a=1;b=2;c=3}

the only visible difference to me is the different datatype of PSCustomObject. Also instead of keys and value properties, a inspection with gm shows that now every key has been added as a NoteProperty object.

But what advantages do I have? I'm able to access my values by using its keys, just like in the hashtable. I can store more than simple key-value pairs (key-object pairs for example) in the PSCustomObject, JUST as in the hashtable. So what's the advantage? Are there any important differences?

Answer 1

One scenario where [PSCustomObject] is used instead of HashTable is when you need a collection of them. The following is to illustrate the difference in how they are handled:

$Hash = 1..10 | %{ @{Name="Object $_" ; Index=$_ ; Squared = $_*$_} }
$Custom = 1..10 | %{[PSCustomObject] @{Name="Object $_" ; Index=$_ ; Squared = $_*$_} }

$Hash   | Format-Table -AutoSize
$Custom | Format-Table -AutoSize

$Hash   | Export-Csv .Hash.csv -NoTypeInformation
$Custom | Export-Csv .CustomObject.csv -NoTypeInformation

Format-Table will result in the following for $Hash:

Name    Value
----    -----
Name    Object 1
Squared 1
Index   1
Name    Object 2
Squared 4
Index   2
Name    Object 3
Squared 9
...

And the following for $CustomObject:

Name      Index Squared
----      ----- -------
Object 1      1       1
Object 2      2       4
Object 3      3       9
Object 4      4      16
Object 5      5      25
...

The same thing happens with Export-Csv, thus the reason to use [PSCustomObject] instead of just plain HashTable.