class my_fw ($ip_version) {
  Firewall <| |> {
    provider => $ip_version == "IPv6" ? { true => 'ip6tables', default => 'iptables'},
  }
  class { ['my_fw::pre', 'my_fw::post']: }
  class { 'firewall':
    ensure => $ip_version == "IPv6" ? { true => 'stopped', default => 'running'},
    ensure_v6 => $ip_version == "IPv6" ? { true => 'running', default => 'stopped'},
  }
}