DynamicParam class example

AlternativeDynamicParamMethod.ps1

Add-Type -TypeDefinition @'
    using System;
    using System.Management.Automation;

    public class DynamicParamExample
    {
        [Parameter()]
        [ValidateSet("one", "two", "three")]
        public string MyDynamicParameter { get; set; }
    }
'@

function Test-Function
{
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]
        [string] $MyStaticParameter
    )

    dynamicparam
    {
        New-Object DynamicParamExample
    }

    end
    {
        $PSBoundParameters
    }
}

Get-Command Test-Function -Syntax

Test-Function -MyStaticParameter Static -MyDynamicParameter three

Note: The dynamicparam block could have logic that chooses between which class to return, etc. This is how Get-ChildItem and other similar cmdlets work, rather than building a RuntimeDefinedParameterDictionary.