How do you pass a hash table to a function in PowerShell?

powershell hashtable
Stéphane picture Stéphane · Oct 17, 2012 · Viewed 49.8k times · Source

When passing a hash table to my PowerShell function, it complains that it receives an object.

Function ExtendHash(){
  param(
    [hashtable] $source,
    [hashtable] $extender
  )
  ...
}

And the caller:

$hash1 = @{One = 1; Two = 2}
$hash2 = @{Two = 22; three = 3}
ExtendHash($hash1, $hash2)

Cannot convert the System.Object[] value of type System.Object[] to type System.Collection.Hashtable

So how do I make this work? Suggestions?

Also, am I missing something built-in? I want the same pattern as what JavaScript uses to extend default options (merge and override default values).

Answer

Roman Kuzmin picture Roman Kuzmin · Oct 17, 2012

Do not use parenthesis and commas. This is PowerShell (say, arguments are similar to arguments of commands in CMD). That is, call your function like this:

ExtendHash $hash1 $hash2

In your case expression ($hash1,$hash2) is an array of two items and you pass this array, one argument, to the function. Such a call fails correctly.

If you use Set-StrictMode -Version 2 then this "common" mistake is caught by PowerShell:

The function or command was called as if it were a method. Parameters should be separated by spaces. For information about parameters, see the about_Parameters Help topic.

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