Powershell error returning hashtable

Question

Anyone have any ideas why the following code would produce an error, see additional comments after the function for more details

function callee    ([Hashtable]$arg0) {
    [Hashtable]$hashtable = @{}
    $hashtable = $arg0
    $hashtable.add('passed', $True)
    # $hashtable                            ######## toggle this line
    $type = $hashtable.GetType()
    Write-Host "$type"
    return $hashtable
}

function caller {
    [Hashtable]$hashtable = @{'00'='0'}
    $hashtable = callee $hashtable        ##### returns error here
    $hashtable.add('returned', $True)
    $hashtable
}
caller

error message: Cannot convert the "System.Object[]" value of type "System.Object[]" to type "System.Collections.Hashtable".

I receive the error on a variety of instances, I tried to narrow it down to an example that is easy to reproduce. It looks like it is changing the hashtable to an object array and that is why it won't return it? It allows me to modify the hashtable and return it but when I try to display it it changes it? This is the same effect I get when I start adding code to the callee function?

Sean Fausett · Accepted Answer · 2010-09-19 03:53:10Z

10

When you uncomment # $hashtable you're outputting two things from the function. The result of the function is everything 'output' from it, and PowerShell will automatically wrap multiple outputs into an array. The return statement is a short-circuit convenience and should not be confused with the only way to return a value from the function.

answered Sep 19, 2010 at 3:53

Sean Fausett

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3 Comments

Sean Fausett Over a year ago

Similar question here stackoverflow.com/questions/2158786/…

Keith Hill Over a year ago

Agreed. I recommend against using the idiom return <expr> in PowerShell because it is misleading. It is functionally equivalent to Write-Output <expr>; return. Best just to put $hashtable as the last line of the function and call it good (just like the caller function does).

Deian Over a year ago

mind you sometimes just a call to some function might trigger output! hence be careful to assign the result to a variable. This way you would remove it from the output. That 'piece' here is critical thing to understand how powershell differs from other languages.

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