PowerShell: Difference [array] vs [array[]]

Question

I need to declare an array parameter in an called PS script. The array coming in from the caller/source script is in a hash table:

$Array = @(1, 2, 3)
$myHashTable = @{myArr = $Array}

Call: Z:\called.ps1 $myHashTable

In 'called.ps1', what is the difference between

Param(
$myArr
)

,

Param(
[array] $myArr
)

and

Param(
[array[]] $myArr
)

?

the 1st will accept any object type. the 2nd will accept most any type, but convert it to an array if not already one. the 3rd accepts most any type - and will convert it to a two-dimensional array. — Lee_Dailey
– Lee_Dailey, Commented Sep 22, 2019 at 20:20

mklement0 · Accepted Answer · 2019-09-22 22:53:54Z

1

You can test that fairly directly. [grin] your examples give ...

any type = remains that type
1d array = converts to an array if not one already
2d array = converts to a jagged array (array of arrays) if not one already

demo code ...

function Test-Parameter
    {
    Param
        (
        $GenericVar,
        [array]$OneD_Array,
        [array[]]$TwoD_Array
        )

    $GenericVar.GetType()
    $OneD_Array.GetType()
    $TwoD_Array.GetType()
    }

Test-Parameter -GenericVar 'One' -OneD_Array 'Two' -TwoD_Array 'Three'

output ...

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     String                                   System.Object
True     True     Object[]                                 System.Array
True     True     Array[]                                  System.Array

edited Sep 22, 2019 at 22:53

mklement0

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answered Sep 22, 2019 at 20:28

Lee_Dailey

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