CodeIgniter：无法在函数内访问$ this

function html_stuff()
{
    $posts = $this->db->query(\'select * from posts\');
}

$this

function html_stuff($ci) {
    $ci->db->query(\'select * from posts\');
}
html_stuff($this);

function html_stuff() {
    $ci = &get_instance();
    $ci->db->query(\'select * from posts\');
}