public function __construct()
{
parent::__construct('list', 'user');
$this->addOption('n|limit:', 'display max n users');
$this->addOption('i|id', 'display id only column');
$this->addOption('s|sort:', 'sort by (username, email or idnumber)');
$this->addOption('d|descending', 'sort in descending order');
$this->addOption('course-inactive', 'limit to users who never accessed course provided with --course.');
$this->addOption('course-role:', 'limit to users with given role in a --course.');
$this->addOption('course:', 'select all enrolled in given course id');
$this->addArgument('sql expression');
$this->minArguments = 0;
}