Global array, feed from a function does not preserve content [duplicate]

Question

I have a loop over data that call a local function.

In this function, I feed an global scoped array.

However, at the end, the array is empty. Why ? and how to fix ?

To reproduce the behavior, try this :

$myArray = @() # Global array

function Invoke-SomeAction{
    param(
        [Parameter()]
        [int]$Val
    )

    $myArray += $Val
}

1..10 | % {

    Invoke-SomeAction -Val $_

}

$myArray.Count # Expect 10, got 0

If I remove the function call like this:

$myArray = @() # Global array

1..10 | % {

    $myArray += $_

}

$myArray.Count # Expect 10, got 10

It behaves as expected.

PS: if it matters, here's my $PSVersionTable:

Name                           Value                                                                                                                           
----                           -----                                                                                                                           
PSVersion                      5.1.14393.3053                                                                                                                  
PSEdition                      Desktop                                                                                                                         
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}                                                                                                         
BuildVersion                   10.0.14393.3053                                                                                                                 
CLRVersion                     4.0.30319.42000                                                                                                                 
WSManStackVersion              3.0                                                                                                                             
PSRemotingProtocolVersion      2.3                                                                                                                             
SerializationVersion           1.1.0.1

Karolina Ochlik · Accepted Answer · 2021-06-02 08:11:22Z

1

The reason is scopes are different. You are trying to add to $myArray in function scope, yet you need to add in script scope. Try this:

$myArray = @() # Global array

function Invoke-SomeAction{
    param(
        [Parameter()]
        [int]$Val
    )
#this sets a variable scope to script 
    $script:myArray += $Val
}

1..10 | % {

    Invoke-SomeAction -Val $_

}

$myArray.Count

More on this here: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_scopes?view=powershell-7.1

edited Jun 2, 2021 at 8:11

answered Jun 2, 2021 at 8:04

Karolina Ochlik

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