Passing an ordered hashtable to a function

Question

How can I go about passing an ordered hashtable to a function?

The following throws an error:

The ordered attribute can be specified only on a hash literal node.

function doStuff {
    Param (
        [ordered]$theOrderedHashtable
    )
    $theOrderedHashtable
}

$datFileWithMinSizes  = [ordered]@{"FileA.DAT" = "4"; "FileB.DAT" = "5"; "FileC.DAT" = "91" ; "FileD.DAT" = "847"  }

doStuff -theOrderedHashtable $datFileWithMinSizes

The following does not maintain the correct order:

function doStuff {
    Param (
        [Hashtable]$theOrderedHashtable = [ordered]@{}
    )
    $theOrderedHashtable
}

$datFileWithMinSizes  = [ordered]@{"FileA.DAT" = "4"; "FileB.DAT" = "5"; "FileC.DAT" = "91" ; "FileD.DAT" = "847"  }

doStuff -theOrderedHashtable $datFileWithMinSizes

The only way I can currently get this to work is by not specifying the type as follows, but I want to specify the type:

function doStuff {
    Param (
        $theOrderedHashtable
    )
    $theOrderedHashtable
}

$datFileWithMinSizes  = [ordered]@{"FileA.DAT" = "4"; "FileB.DAT" = "5"; "FileC.DAT" = "91" ; "FileD.DAT" = "847"  }

doStuff -theOrderedHashtable $datFileWithMinSizes

Answer 1

Use the full type name:

function Do-Stuff {
    param(
        [System.Collections.Specialized.OrderedDictionary]$OrderedHashtable
    )
    $OrderedHashtable
}

To support both regular hashtables and ordered dictionaries, you'll have to use separate parameter sets: use the [System.Collections.IDictionary] interface, as suggested by briantist

function Do-Stuff {
    [CmdletBinding(DefaultParameterSetName='Ordered')]
    param(
        [Parameter(Mandatory=$true,Position=0,ParameterSetName='Ordered')]
        [System.Collections.Specialized.OrderedDictionary]$OrderedHashtable,

        [Parameter(Mandatory=$true,Position=0,ParameterSetName='Hashtable')]
        [hashtable]$Hashtable
    )
    if($PSCmdlet.ParameterSetName -eq 'Hashtable'){
        $OrderedHashtable = $Hashtable
    }
    $OrderedHashtable
}