Tuples In Powershell

Tuples in computer science are usually light weight record objects with simple name value pairs. In scripting languages it is very handy to create them on the fly. For quite some time I was using associative arrays in PowerShell to do just that.

PS>$a = @{Name="MyName";Value="MyValue"}

It has essentially everything you would need from a tuple inside of a scripting language. The more and more I use PowerShell though I’ve found that this is not always a good idea. It comes back to PowerShell pipelining. Whenever you pass a collection to a pipeline PowerShell will unroll the collection and pass the individual items.

Under the hood, an associative array is a System.Hashtable. As a result it is a collection of name value pairs. Hence when you pass this tuple through a pipeline, it is torn apart and each element of the tuple is passed as a separate object.

PS>$a = @{Name1="Value1";Name2="Value2"}
PS>$a

Name                           Value
----                           -----
Name2                          Value2
Name1                          Value1

Hence I’ve now taken a new route. Create an actual tuple :)

function New-Tuple()  
{  
    param ( [object[]]$list= $(throw "Please specify the list of names and values") ) 

    $tuple = new-object psobject  
    for ( $i= 0 ; $i -lt $list.Length; $i = $i+2)  
    {  
        $name = [string]($list[$i])  
        $value = $list[$i+1]  
        $tuple | add-member NoteProperty $name $value  
    } 

    return $tuple  
}

PS>$a = New Tuple Name,1,Value,2

The result can now be passed around pipelines as a single entity.