So you noticed that when you pipe some cmdlets to the Select-Object cmdlet, you can hit the TAB key and enumerate all properties of the former cmdlet.

And this works with other cmdlets too. Here is a non-exhaustive list:

• ForEach-Object
• Format-Custom
• Format-List
• Format-Table
• Format-Wide
• Measure-Object
• Select-Object
• Sort-Object
• Where-Object

Now you want to do the same with your function/script/cmdlet but it doesn’t work… Huh!

Let’s work on a simple example:

function test{
    param(
        [int]$Number
    )

    [PSCustomObject]@{
        InitialNumber = $Number
        Twice = $Number * 2
    }
}

This basic function takes the number you give as a parameter and computes the double.

2 steps

Step one: Use the OutputType attribute

All the cmdlets listed above use the OutputType attribute from the former cmdlet/function/script to know which type of object is coming down the pipeline.
So you have to declare it before the param() section.

function test{

    [outputtype('MyType')]

    param(
        [int]$Number
    )

    [PSCustomObject]@{
        InitialNumber = $Number
        Twice = $Number * 2
    }
}

But which type will you declare?
Because you are really outputting a PSCustomObject you would be tempted to declare a PSCustomObject.
But as you notice, you won’t get the expected properties…

In fact, you get the properties of a basic PSCustomObject, and what you want are 2 properties:

• InitialNumber
• Twice

Step two: Create your own class

Please stay here for a few more seconds! You don’t need to be a “class” expert to make the second step. It is really easy.

Before the function section, create a class section (which looks like a Param() section) and name it with your own type. And this is the type name you will use for the OutputType attribute.

class MyType{
    [int]$InitialNumber
    [int]$Twice
}

function test{

    [OutputType('MyType')]

    param(
        [int]$Number
    )

    [PSCustomObject]@{
        InitialNumber = $Number
        Twice = $Number * 2
    }
}

That’s it :)