Powershell - how to declare an array for use with += operator - arrays

Question

I can intuitively figure out most languages, but apparently not Powershell.
I want to create an array of arrays (this will contain disk directories and a count so later I can verify we have at least that many files).
From that array of arrays, I want to pull out a single array of just the directory names so I can pass it to Get-ChildItem.
$DirInfo = #('d:\Work',2),
('d:\Temp',3)
$DirNameArray=#() #declare empty array
foreach ($item in $DirInfo)
{
$DirNameArray += , $item[0] #tried with and without the comma here
Write-Host 'Loop1 ' $item[0]
}
write-host $DirNameArray.count
#Let's Verify what we got so we know how many items we have in our array
Write-Host "Verify with a loop"
foreach ($dir in $DirNameArray)
{
Write-Host 'Loop2:' $dir
}
Write-Host "Verify the other way"
Write-Host $DirNameArray
Actual Results:
Loop1 d:\Work
Loop1 d:\Temp
1
Verify with a loop
Loop2: d:\Workd:\Temp
Verify the other way
d:\Workd:\Temp
What I don't understand is why Loop2 didn't execute twice.
It looks like the =+ is just stringing together the values instead of adding a new item to my array called $DirNameArray.
I'm still utterly baffled, one file I created does this and gives me the expected results:
$a = "one","two"
Write-Host $a.count
$a += "three"
Write-Host $a.count
Results:
2
3
So if the above worked, why didn't my code work?
A second file I created does this - and I don't understand the results. I even made the variable name different so I wouldn't be dealing with any prior definition or values of that variable:
$DirNameArray5="abc","def"
write-host $DirNameArray5.count
$DirNameArray5 += "xyz"
write-host $DirNameArray5.count
$DirNameArray5 += #("opq")
write-host $DirNameArray5.count
Results:
1
1
1
$DirNameArray7="abc","def"
write-host $DirNameArray7.count
$DirNameArray7 += "xyz"
write-host $DirNameArray7.count
$DirNameArray7 += #("opq")
write-host $DirNameArray7.count
Results:
2
3
4
So apparently, if you once define a variable as a string, it's hard to get Powershell to redefine it as an array.
But I still have my original question. How to define an empty array so I can add to it in a loop using the += operator.
$DirNameArray=#()
I finally used the .GetType() method to see what my variables actually were:
PS C:\Users\nwalters> $DirNameArray5.GetType()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True String System.Object
PS C:\Users\nwalters> $DirNameArray7.GetType()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True Object[] System.Array
Bottom line - this is what I want to do - in as few lines of code as possible with no loop:
[string]$x=#() # declare empty array
Write-Host $x.GetType()
$x += "one"
$x += "two"
Write-Host $x.count
Write-Host $x
Actual Results
System.String
1
onetwo
Desired Results:
object[] or string[]???
2
one two

Answer 1

Powershell will not let you create an empty array, or let you empty an array down to nothing (with one exception). There are two ways I have discovered to work around this issue:
Method 1: Use -OutVariable to a new variable name to create an array with your input
Example: gci C:\TestDir1 -OutVariable test
Using the .GetType() method returns:
$test.GetType()
Directory: C:\TestDir1
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a---- 4/20/2020 11:36 AM 8015 Test1.xls
-a---- 6/26/2020 12:59 PM 0 test2.txt
Module : CommonLanguageRuntimeLibrary
Assembly : mscorlib, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089
TypeHandle : System.RuntimeTypeHandle
DeclaringMethod :
BaseType : System.Object
UnderlyingSystemType : System.Collections.ArrayList
FullName : System.Collections.ArrayList
This will create a new variable named $test that is an array (since there are multiple items in it). $test.gettype() shows the object as an array.
Method 2: Explicitly declare an array with two dummy objects and then remove both dummy objects.
[System.Collections.ArrayList]$array = "value1", "value2"
$array.remove("value1")
$array.remove("value2")
Using the gettype method will still show $test is an array even though it is empty:
> $test.GetType()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True ArrayList System.Object
The array will now be completely empty and can be used to store any new input. This doesn't work unless you explicitly name the variable type like I did in my example (not sure why). Example shown below:
$test = "value1", "value2"
$test.Remove("value1")
Exception calling "Remove" with "1" argument(s): "Collection was of a fixed size."
At line:3 char:1
+ $test.Remove("value1")
+ ~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : NotSupportedException
P.S. I know this is an old thread, but it is unanswered and I just came upon this issue myself so I am answering it for anyone else that searches this issue.

Answer 2

The following code is tested on two different computers, both with PowerShell 2.0. Can you try this and post results.
# declare an empty array
$var = #()
write-host "var.count = '$($var.count)' var.type ='$($var.GetType())' var.type.BaseType = '$($var.GetType().BaseType)'"
# add a single item
$var += "single item"
write-host "var.count = '$($var.count)' var.type ='$($var.GetType())' var.type.BaseType = '$($var.GetType().BaseType)'"
# add an array
$var += , #("array 1 - item 1","array 1 - item 2")
write-host "var.count = '$($var.count)' var.type ='$($var.GetType())' var.type.BaseType = '$($var.GetType().BaseType)'"
# display the 'single item'
write-host "single item = '$($var[0])'"
# display first element of array item
write-host "first element of array item = '$($var[1][0])'"
gives me
var.count = '0' var.type ='System.Object[]' var.type.BaseType = 'array'
var.count = '1' var.type ='System.Object[]' var.type.BaseType = 'array'
var.count = '2' var.type ='System.Object[]' var.type.BaseType = 'array'
single item = 'single item'
first element of array item = 'array 1 - item 1'