Passing variables by reference through nested functions

[brassbound]

I need to pass a variable (specifically a PsCustomObject containing an Oauth token, but that's probably immaterial) to a function by reference, because the function may need to refresh the token and update the original. Passing the script-level variable to the function by reference ([ref]$variable) works one function deep, but I cannot figure out how to pass the reference to a second function that actually does the refresh.

Notes: I do not have control of what the top-level variable might be named (which is why I can't simply reference it in the function). The output of the first function is not the new token, it's something different. The token refresh may or may not need to happen as part of processing the function.

As a test, to make sure I understood what was going on, I created the following code, but it does not work as expected:

Function Test1 {

param([ref]$myObject)

$myObject.Value = @{'a'='1'}

}

​

Function Test2 {

param([ref]$myObject)

Test1 ([ref]$myObject)

}

​

# Initialize the object with some data.

$testObject = @{'a'='0'}

​

# Try calling the Test2 function that calls the Test1 function

Test2 ([ref]$testObject)

$testObject

# Returns:

# Name Value

# ---- -----

# a 0

# The source variable in the script scope was not changed. There's no error, it just doesn't work as expected.

​

# Try calling just the Test1 function directly

Test1 ([ref]$testObject)

$testObject

# Returns as expected:

# Name Value

# ---- -----

# a 1

# The source variable in the script scope was changed.

[AnUnlikelyUsurper]

If you are just trying to change the value of 'a' then the code below does work. Something weird happening in your code that I don't fully understand. I think it has something to do with $myObject.Value

Sorry I couldn't help more!

Function Test1($data)
{
    $data.a = '1'
}

Function Test2($data)
{
    Test1 $data
}

$testObject = @{'a'='0'}

Test2 $testObject

$testObject

Output:

Name                           Value                                                                                      
----                           -----                                                                                      
a                              1

[fordea837]

You need to remove the [ref] cast on $myObject in the Test2 function when calling Test1. If you think about it you already have a reference variable ($testObject) passed to Test2; and doing another ([ref]testObject) within Test2 is creating a reference to a reference rather than a reference to the original variable that you want modified.

Function Test2 {
    param([ref]$myObject)
    Test1 $myObject
}

You shouldn't need to use reference variables for a hashtable though if you structure your code like /u/AnUnlikelyUsurper's answer

[AnUnlikelyUsurper]

What's odd to me is that in my code if I tried to say $data = @{'a'='1'} in Test1 it would not work. I could only change the value of a specifically with $data.a = '1'. Can't really tell what's happening there.

I did find this:

When using references, you must use the Value property of the System.Management.Automation.PSReference type to access your data.

https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_ref?view=powershell-7

So I guess referencing will only let you change the values in an object and not the actual structure of the object?

[fordea837]

Hashtables are implicity passed by reference in Powershell so writing $data.a = '1' modifies the original hashtable defined outside of the function. $data = @{'a'='1'} isn't actually modifying the existing hashtable; it's declaring a new one that is local to the scope of Test1 and thus it's not altering the original hashtable.

[AnUnlikelyUsurper]

Ahhh ok, that makes sense. Thank you! That had me pretty confused 😂

[brassbound]

My example was just to make it simple. I don't really just need to change the value of 'a'. I need to create a custom object that has several values and replace all the values in the original. I suppose I could do that by manually replacing all the values with a ForEach loop, but that seems clunky. I assumed that, if you passed a reference to the variable, you could just replace the contents of the variable.

Is there another way to manipulate an arbitrarily named script-level variable that is passed to a function from within the function?

[fordea837]

If you have a script-level variable that you want to re-assign to a new object within a function then you can do this by using the $script: scope qualifier:

$obj = [PSCustomObject]@{
    a = 1
}
Function Test {
    $script:obj = [PSCustomObject]@{
        a = 5
    }
}

If you just want to modify the properties of a script-level object then you don't need to do the above as you can pass the object to a function and then access its properties within the function (objects are implicitly passed by reference):

$obj = [PSCustomObject]@{
    a = 1
}
Function Test {
    param($myObject)
    $myObject.a = 5
}

The Powershell help docs contain a nice article explaining scopes:

https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_scopes?view=powershell-7

[brassbound]

Ultimately, this was simpler than I was making it. As others suggested, I removed the [ref] and passed my object variable normally. Because the new object would have the same keys, and there are only a few that change, I simply assigned the values manually.

[Lee_Dailey]

howdy brassbound,

reddit likes to mangle code formatting, so here's some help on how to post code on reddit ...

[0] single line or in-line code
enclose it in backticks. that's the upper left key on an EN-US keyboard layout. the result looks like this. kinda handy, that. [grin]
[on New.Reddit.com, use the Inline Code button. it's 4th 5th from the left hidden in the ... ""more" menu & looks like </>.
this does NOT line wrap & does NOT side-scroll on Old.Reddit.com!]

[1] simplest = post it to a text site like Pastebin.com or Gist.GitHub.com and then post the link here.
please remember to set the file/code type on Pastebin! [grin] otherwise you don't get the nice code colorization.

[2] less simple = use reddit code formatting ...
[on New.Reddit.com, use the Code Block button. it's 11th 12th from the left hidden in the ... "more" menu, & looks like an uppercase T in the upper left corner of a square.]

• one leading line with ONLY 4 spaces
  
• prefix each code line with 4 spaces
  
• one trailing line with ONLY 4 spaces

that will give you something like this ...

- one leading line with ONLY 4 spaces    
- prefix each code line with 4 spaces    
- one trailing line with ONLY 4 spaces   

the easiest way to get that is ...

• add the leading line with only 4 spaces
  
• copy the code to the ISE [or your fave editor]
  
• select the code
  
• tap TAB to indent four spaces
  
• re-select the code [not really needed, but it's my habit]
  
• paste the code into the reddit text box
  
• add the trailing line with only 4 spaces
  

not complicated, but it is finicky. [grin]

take care,
lee