dynamic regex switch (PowerShell)

dynamic.regex.switch.ps1

[string[]] $a = ( 
    "  asd",
    "    asd ",
    "      bsd",
    "    XXX",
    "10000"
)

[string] $spacer = ""

$a | ForEach-Object {
    switch -Regex ($_) {
        "^\s+" {
            ($spacer.Length -lt $Matches[0].Length) -and ( $spacer = $Matches[0] ) | out-null
        }

        "^$spacer" {
            Write-Host Spacer with length $($spacer.Length) is present in [$_]
        }

        default { 
            Write-Host Spacer with length $($spacer.Length) is NOT present in [$_]           
        }
     }
}