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Discover how to effectively handle output from PowerShell functions to avoid `Object[]` casting issues with PSObjects.
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This video is based on the question https://stackoverflow.com/q/63902886/ asked by the user 'moutonjr' ( https://stackoverflow.com/u/1716568/ ) and on the answer https://stackoverflow.com/a/63903267/ provided by the user 'Mike Shepard' ( https://stackoverflow.com/u/36429/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Weird Object[] Casting from PSObject in PowerShell

When coding in PowerShell, encountering unexpected output types can be disruptive to your workflow. One common problem users face is the casting of a PSObject into an Object[] unexpectedly. In this guide, we will dive into a specific case where this occurs, particularly when dealing with ADO and EML attachments. We will also provide clear solutions to avoid such situations in your scripts.

The Problem: Unexpected Object[] Return Type

Let’s begin by outlining the situation presented by a user trying to create a PowerShell function that retrieves attributes from an EML email attachment. The user defined a function called Get-OriginalMailAttributes, which successfully creates and returns a PSObject containing email attributes. However, when retrieving the From property, the user is surprised to find that the output is not as expected — it results in an Object[] type.

Here’s the characteristic behavior noticed by the user:

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The output is an empty array rather than the anticipated value of the From property. The key to resolving this issue lies in understanding the source of extra values returned by functions in PowerShell.

The Root Cause of the Issue

When PowerShell functions generate output, they can sometimes return additional "extra" values. This often happens when methods are invoked that have return values. For instance, the .Add() method is notorious for returning the index of the added item, leading to the wrapping of expected outputs within an array instead of returning a single object as anticipated.

In this instance, although the code does not explicitly invoke an .Add() method, other operations may inadvertently cause this behavior, leading to the return of an Object[] type instead of a single PSObject.

Solutions to Prevent Object[] Casting Issues

To resolve the unexpected behavior and ensure the function returns just the desired PSObject, you can adopt one of several approaches outlined below:

Method 1: Cast to Void

One effective approach is to ensure that any method calls that could return extra output are cast to [void]:

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This method signifies that you are intentionally disregarding the output of the operation.

Method 2: Assign to Null

Another straightforward method is to assign the output to $null:

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This effectively ignores any returned values while keeping your code clean.

Method 3: Pipe to Out-Null

If you're looking to suppress output, you may also pipe the command to Out-Null:

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This method discards the output completely without impacting the function's behavior.

Debugging Tips

To further diagnose where the extra object output may be originating from, you can use debugging statements effectively. Insert simple output commands throughout your function, like so:

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This technique helps pinpoint specific lines generating unintended outputs and allows for more accurate troubleshooting.

Conclusion

Casting issues with PSObjects in PowerShell can lead to confusion, particularly when dealing with method outputs inadvertently returning extra values. By applying methods to suppress or discard unwanted output, you can maintain a clean and expected return from your functions. Embrace these solutions to streamline your PowerShell coding process and reduce the potential for similar casting issues in the future.

With these insights, you are now equipped to tackle Weird Object[] casting from PSObject issues confidently in your PowerShell scripts.