gistfile1.pp

$groups = ['adm', 'plugdev']
$user = 'foo'
$users = [$user]

# method 1

user { $user:
	groups => $groups,
}

# method 2

define manager(
  $groups
) {
	user { $name:
		groups => $groups,
	}
}

manager { $users: 
  groups => $groups,
}