php - Mysqli prepared statement function in class -

i want make prepared statement function in class, how make dry code. after this, want try make crud system prepared statements, 1 thing bogus me..

//class method

        public function insert($sql, $types=array()){                 $count = count($types);                 $params = implode(',', $types);                 $stmt = mysqli_prepare($this->link, $sql);                  mysqli_stmt_bind_param($stmt, $params, ???);                  mysqli_stmt_execute($stmt);              } $sql = "insert users (username, password,date_reg) values(?,?, now())"; $arr= array('s','s'); $db->insert($sql, $arr); 

so.. in line mysqli_stmt_bind_param($stmt, $params, ???); how can complete statement, 3rd parameter works (i need insert variables bind params) sorry bad english..