Passing an foreachable array from C# to PowerShell

Question

How can I pass an array from C# to PowerShell that can be foreached?

Right now I have this script:

[Cmdlet(VerbsCommon.Get, "Numbers")]
public class GetNumbersCmdlet: Cmdlet
{
    protected override void BeginProcessing()
    {
        var list = new List<string>();
        list.Add("1");
        list.Add("2");
        list.Add("3");
        list.Add("4");
        list.Add("5");
        WriteObject(results.ToArray());
    }
}

And this PowerShell script:

foreach ($number in Get-Numbers) {
    Write-Output "Output is $number"
}

Instead of:

Output is 1
Output is 2
Output is 3
Output is 4
Output is 5

I would get:

Output is 1 2 3 4 5

So if I pull out Get-Numbers and assign the results to a variable first then foreach that variable, everything works as intended. I've filed a bug report here. — tyteen4a03
– tyteen4a03, Commented Sep 12, 2017 at 10:57

user4003407 · Accepted Answer · 2017-09-16 10:55:59Z

PowerShell do not automatically enumerate output of commands. That means if command write collection into pipeline, then that collection will be passed to the next command as single object.

WriteObject also do not enumerate objects unless explicitly asked.

So to solve your problem, you can write objects as you go instead of collecting them:

[Cmdlet(VerbsCommon.Get, "Numbers")]
public class GetNumbersCmdlet: Cmdlet
{
    protected override void BeginProcessing()
    {
        WriteObject("1");
        WriteObject("2");
        WriteObject("3");
        WriteObject("4");
        WriteObject("5");
    }
}

Or you can ask WriteObject to enumerate your collection:

[Cmdlet(VerbsCommon.Get, "Numbers")]
public class GetNumbersCmdlet: Cmdlet
{
    protected override void BeginProcessing()
    {
        var list = new List<string>();
        list.Add("1");
        list.Add("2");
        list.Add("3");
        list.Add("4");
        list.Add("5");
        WriteObject(results, true);
    }
}

Note that in both cases you are not writing array anymore, but individual items of it.

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