Question

PowerShell 3.0 CTP1 introduces a new feature [ordered] which is somewhat a shortcut for OrderedDictionary. I cannot imagine practical use cases of it. Why is this feature really useful? Can somebody provide some useful examples?

Example: this is, IMHO, rather demo case than practical:

$a = [ordered]@{a=1;b=2;d=3;c=4}

(I do not mind if it is still useful, then I am just looking for other useful cases).

I am not looking for use cases of OrderedDictionary, it is useful, indeed. But we can use it directly in v2.0 (and I do a lot). I am trying to understand why is this new feature [ordered] needed in addition.

---

Collected use cases from answers:

$hash = [ordered]@{}

is shorter than

$hash = New-Object System.Collections.Specialized.OrderedDictionary

N.B. ordered is not a real shortcut for the type. New-Object ordered does not work.

N.B. 2: But this is still a good shortcut because (I think, cannot try) it creates typical for PowerShell case insensitive dictionary. The equivalent command in v2.0 is too long, indeed:

New-Object System.Collections.Specialized.OrderedDictionary]([System.StringComparer]::OrdinalIgnoreCase)

Answer 1

First I will start by asking – Why not have them?

I can think of a use case in my project where we use Powershell scripts for build and deploy and yml for config ( using https://github.com/scottmuc/PowerYaml )

The config from yml is read in as hashtables. The tasks are specified in the yml like deploy to database, deploy to iis, deploy service and so on. I would like to do the database deploy and then website deploy so that I can avoid iisreset afterwards. Currently I have to explicitly look at that. Now, I can have an Ordered hash table and specify the deploy database first and hence it happens first.

Snippet:

function Convert-YamlMappingNodeToHash($node)
{
    $hash = @{}
    $yamlNodes = $node.Children

    foreach($key in $yamlNodes.Keys)
    {
        $hash[$key.Value] = Explode-Node $yamlNodes[$key]
    }
    return $hash
}

Now the $hash =@{} become $hash=[ordered]@{}

I don’t know how this means for a bloated product. OrderedDictionary is there in .NET ( I have lots of use cases for it in programming ) and they have just added an accelerator for it.