Get-DistinctUnion.ps1

function Get-DistinctUnion
{
    param(
        [array]$Source,
        [array]$Other
    )

    $temp = [System.Collections.Generic.HashSet[object]]::new($Source)
    $temp.UnionWith($Other)

    return $temp
}

$array1 = 1..3
$array2 = 3..5

Get-DistinctUnion -Source $array1 -Other $array2

# This will also work
$set1 = [System.Collections.Generic.HashSet[int]]::new([int[]]$array1)
$set2 = [System.Collections.Generic.HashSet[int]]::new([int[]]$array2)

Get-DistinctUnion -Source $set1 -Other $set2