Passing Powershell Arrays by-reference not working as intended - arrays

Question

Arrays by reference
Working fine!
The normal way to pass an Array by-reference in PowerShell seems to work fine:
Function Swap-Array ($theArray, $theArrayB, [int]$indexToSwap) {
$temp = $theArrayA[$indexToSwap];
$theArrayA[$indexToSwap] = $theArrayB[$indexToSwap];
$theArrayB[$indexToSwap] = $temp;
}
$a = #(1,2,3,4)
$b = #(3,2,4,1)
$a
$b
Swap-Array $a, $b, 2
$a
$b
Output:
a
-
1
2
3
4
b
-
3
2
4
1
a
-
1
2
4
3
b
-
3
2
3
1
The problem
Adding Objects
The issue arises when the array by-refernece is a container of PSObjects that's not static, and I am attempting to add a new record. Modifying the existing records seems to be fine!
Function Swap-Apples($objectA, $objectB, $indexToSwap) {
$temp = $objectA[$indexToSwap].Apples;
$objectA[$indexToSwap].Apples = $objectB[$indexToSwap].Apples;
$objectB[$indexToSwap].Apples = $temp;
}
Function Swap-Oranges($objectA, $objectB, $indexToSwap) {
$temp = $objectA[$indexToSwap].Oranges;
$objectA[$indexToSwap].Oranges = $objectB[$indexToSwap].Oranges;
$objectB[$indexToSwap].Oranges = $temp;
}
<# heres the problematic bit #>
Function Add-Fruit ($object, [int]$howManyApples, [int]$howManyOranges) {
$hAdd = #{
Apples=$howManyApples
Oranges=$howManyOranges
}
$hToAdd = New-Object -TypeName PSObject -Property $hAdd;
$object += $hToAdd;
}
$a = #();
$b = #();
$a1 = #{
Apples=3
Oranges=2
}
$b1 = #{
Apples=5
Oranges=7
}
$a2 = #{
Apples=6
Oranges=3
}
$b2 = #{
Apples=1
Oranges=5
}
$aObject1 = New-Object -TypeName PSObject -Property $a1;
$bObject1 = New-Object -TypeName PSObject -Property $b1;
$aObject2 = New-Object -TypeName PSObject -Property $a2;
$bObject2 = New-Object -TypeName PSObject -Property $b2;
$a += $aObject1; $a += $aObject2;
$b += $bObject1; $b += $aObject2;
Write-Host "Values of A";
$a | Format-List
Write-Host "Values of B";
$b | Format-List
Write-Host "Now lets make a trade`!";
Swap-Apples $a $b 0
Swap-Oranges $a $b 1
Write-Host "Values of A";
$a | Format-List
Write-Host "Values of B";
$b | Format-List
Write-Host "Hey, I brought more fruit for A`!";
Add-Fruit -object $a -howManyApples 5 -howManyOranges 2
Write-Host "Values of A";
$a | Format-List
Write-Host "I brought more fruit for B too`!";
Add-Fruit -object $b -howManyApples 5 -howManyOranges 3
Write-Host "Values of B";
$b | Format-List
Output
Values of A
Oranges : 2
Apples : 3
Oranges : 3
Apples : 6
Values of B
Oranges : 7
Apples : 5
Oranges : 3
Apples : 6
Now lets make a trade!
Values of A
Oranges : 2
Apples : 5
Oranges : 3
Apples : 6
Values of B
Oranges : 7
Apples : 3
Oranges : 3
Apples : 6
Hey, I brought more fruit for A!
Values of A
Oranges : 2
Apples : 5
Oranges : 3
Apples : 6
I brought more fruit for B too!
Values of B
Oranges : 7
Apples : 3
Oranges : 3
Apples : 6
The Swap-Apples and Swap-Oranges Functions seem to work fine. The program falls apart at the last segment, trying to give both A and B more fruit ! This would otherwise normally work in Local Scope. I feel like this is falling apart due to by-reference passing.
How would I go about fixing the problem at the end of this program ?

Answer 1

The Solution
Dynamic ArrayLists
In PowerShell, you can create arrays of both fixed-size and dynamically allocated. If I would like to give both A and B more objects, I have to tell PowerShell that this is an ArrayList and not the typical standard Array.
This means I cannot declare my array like this:
$a = #();
$b = #();
This type in .NET is called System.Collections.ArrayList and can be passed by-reference in a PowerShell program, like so:
$a = New-Object -TypeName 'System.Collections.ArrayList';
$b = New-Object -TypeName 'System.Collections.ArrayList';
Now its not fixed-size, so I can add records anywhere in my program at my leasure, even by reference!
Here is the solution:
Function Swap-Apples($objectA, $objectB, $indexToSwap) {
$temp = $objectA[$indexToSwap].Apples;
$objectA[$indexToSwap].Apples = $objectB[$indexToSwap].Apples;
$objectB[$indexToSwap].Apples = $temp;
}
Function Swap-Oranges($objectA, $objectB, $indexToSwap) {
$temp = $objectA[$indexToSwap].Oranges;
$objectA[$indexToSwap].Oranges = $objectB[$indexToSwap].Oranges;
$objectB[$indexToSwap].Oranges = $temp;
}
<# ArrayList! #>
Function Add-Fruit ([System.Collections.ArrayList]$object, [int]$howManyApples, [int]$howManyOranges) {
$hAdd = #{
Apples=$howManyApples
Oranges=$howManyOranges
}
$hToAdd = New-Object -TypeName PSObject -Property $hAdd;
<# We have to call the ArrayList Add method to add to our dynamic object #>
$object.Add($hToAdd);
}
$a = New-Object -TypeName 'System.Collections.ArrayList';
$b = New-Object -TypeName 'System.Collections.ArrayList';
$a1 = #{
Apples=3
Oranges=2
}
$b1 = #{
Apples=5
Oranges=7
}
$a2 = #{
Apples=6
Oranges=3
}
$b2 = #{
Apples=1
Oranges=5
}
$aObject1 = New-Object -TypeName PSObject -Property $a1;
$bObject1 = New-Object -TypeName PSObject -Property $b1;
$aObject2 = New-Object -TypeName PSObject -Property $a2;
$bObject2 = New-Object -TypeName PSObject -Property $b2;
<# Here we call the ArrayList Add method #>
$a.Add($aObject1); $a.Add($aObject2);
$b.Add($bObject1); $b.Add($aObject2);
Write-Host "Values of A";
$a | Format-List
Write-Host "Values of B";
$b | Format-List
Write-Host "Now lets make a trade`!";
Swap-Apples $a $b 0
Swap-Oranges $a $b 1
Write-Host "Values of A";
$a | Format-List
Write-Host "Values of B";
$b | Format-List
Write-Host "Hey, I brought more fruit for A`!";
Add-Fruit -object $a -howManyApples 5 -howManyOranges 2
Write-Host "Values of A";
$a | Format-List
Write-Host "I brought more fruit for B too`!";
Add-Fruit -object $b -howManyApples 5 -howManyOranges 3
Write-Host "Values of B";
$b | Format-List
And the (somewhat) intended output (see below):
0
1
0
1
Values of A
Oranges : 2
Apples : 3
Oranges : 3
Apples : 6
Values of B
Oranges : 7
Apples : 5
Oranges : 3
Apples : 6
Now lets make a trade!
Values of A
Oranges : 2
Apples : 5
Oranges : 3
Apples : 6
Values of B
Oranges : 7
Apples : 3
Oranges : 3
Apples : 6
Hey, I brought more fruit for A!
Values of A
Oranges : 2
Apples : 5
Oranges : 3
Apples : 6
Oranges : 2
Apples : 5
I brought more fruit for B too!
Values of B
Oranges : 7
Apples : 3
Oranges : 3
Apples : 6
Oranges : 3
Apples : 5
Extra output ?
If you observed in the output:
0
1
0
1
The Add Method of ArrayList returns the index of the record you Added. Since it returns this value it drops out of your pipe into Std-Out, so make sure you direct it accordingly.
If you don't need this output in your program like I don't here, pipe it to the null device, like so:
$a.Add($aObject1) | Out-Null; $a.Add($aObject2) | Out-Null;
$b.Add($bObject1) | Out-Null; $b.Add($aObject2) | Out-Null;
And here's the final program/output:
Code: (Arraytest.ps1)
Function Swap-Apples($objectA, $objectB, $indexToSwap) {
$temp = $objectA[$indexToSwap].Apples;
$objectA[$indexToSwap].Apples = $objectB[$indexToSwap].Apples;
$objectB[$indexToSwap].Apples = $temp;
}
Function Swap-Oranges($objectA, $objectB, $indexToSwap) {
$temp = $objectA[$indexToSwap].Oranges;
$objectA[$indexToSwap].Oranges = $objectB[$indexToSwap].Oranges;
$objectB[$indexToSwap].Oranges = $temp;
}
<# ArrayList! #>
Function Add-Fruit ([System.Collections.ArrayList]$object, [int]$howManyApples, [int]$howManyOranges) {
$hAdd = #{
Apples=$howManyApples
Oranges=$howManyOranges
}
$hToAdd = New-Object -TypeName PSObject -Property $hAdd;
<# We have to call the ArrayList Add method to add to our dynamic object #>
$object.Add($hToAdd) | Out-Null;
}
$a = New-Object -TypeName 'System.Collections.ArrayList';
$b = New-Object -TypeName 'System.Collections.ArrayList';
$a1 = #{
Apples=3
Oranges=2
}
$b1 = #{
Apples=5
Oranges=7
}
$a2 = #{
Apples=6
Oranges=3
}
$b2 = #{
Apples=1
Oranges=5
}
$aObject1 = New-Object -TypeName PSObject -Property $a1;
$bObject1 = New-Object -TypeName PSObject -Property $b1;
$aObject2 = New-Object -TypeName PSObject -Property $a2;
$bObject2 = New-Object -TypeName PSObject -Property $b2;
<# Here we call the ArrayList Add method #>
$a.Add($aObject1) | Out-Null; $a.Add($aObject2) | Out-Null;
$b.Add($bObject1) | Out-Null; $b.Add($aObject2) | Out-Null;
Write-Host "Values of A";
$a | Format-List
Write-Host "Values of B";
$b | Format-List
Write-Host "Now lets make a trade`!";
Swap-Apples $a $b 0
Swap-Oranges $a $b 1
Write-Host "Values of A";
$a | Format-List
Write-Host "Values of B";
$b | Format-List
Write-Host "Hey, I brought more fruit for A`!";
Add-Fruit -object $a -howManyApples 5 -howManyOranges 2
Write-Host "Values of A";
$a | Format-List
Write-Host "I brought more fruit for B too`!";
Add-Fruit -object $b -howManyApples 5 -howManyOranges 3
Write-Host "Values of B";
$b | Format-List
Output:
Values of A
Oranges : 2
Apples : 3
Oranges : 3
Apples : 6
Values of B
Oranges : 7
Apples : 5
Oranges : 3
Apples : 6
Now lets make a trade!
Values of A
Oranges : 2
Apples : 5
Oranges : 3
Apples : 6
Values of B
Oranges : 7
Apples : 3
Oranges : 3
Apples : 6
Hey, I brought more fruit for A!
Values of A
Oranges : 2
Apples : 5
Oranges : 3
Apples : 6
Oranges : 2
Apples : 5
I brought more fruit for B too!
Values of B
Oranges : 7
Apples : 3
Oranges : 3
Apples : 6
Oranges : 3
Apples : 5

Answer 2

It works to me:
Function Swap-Array ($theArrayA, $theArrayB, [int]$indexToSwap)
{
$temp = $theArrayA[$indexToSwap]
$theArrayA[$indexToSwap] = $theArrayB[$indexToSwap]
$theArrayB[$indexToSwap] = $temp
}
$a = #(1,2,3,4)
$b = #(3,2,4,1)
$a
$b
Swap-Array $a $b 2
$a
$b
Just remove the comas.