Validating input

PowerShell provides a variety of different ways to tightly define the content for a parameter. Assigning a .NET type to a parameter is the first of these. If a parameter is set as [String], it will only ever hold a value of that type. PowerShell will attempt to coerce any values passed to the parameter into that type.

The PSTypeName attribute

The PSTypeName attribute can test the type name assigned to a custom object.

It is not uncommon in PowerShell to want to pass an object created in one command, as a PSObject (or PSCustomObject), to another.

Type names are assigned by setting (or adding) a value to the hidden PSTypeName property. There are several ways to tag PSCustomObject with a type name.

The simplest is to set a value for a PSTypeName property, shown as follows:

$object = [PSCustomObject]@{
    Property   = 'Value'
    PSTypeName = 'SomeTypeName'
}

The PSTypeName property does not exist on the resulting object...