未定义的类常量＆＃39; FETCH_ASSCOC＆＃39;使用PDO连接数据库时

Question

这是一行，我收到错误：

PDO::ATTR_DEFAULT_FETCH_MODE    => PDO::FETCH_ASSCOC,

有完整的代码：

<?php

class CON {

public static function db() {

$host = "127.0.0.1";
$db = "4";
$user = "danny";
$password = "censored";
$charset = "utf8";

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$opt = [
  PDO::ATTR_ERRMODE               => PDO::ERRMODE_EXCEPTION,
  PDO::ATTR_DEFAULT_FETCH_MODE    => PDO::FETCH_ASSCOC,
  PDO::ATTR_EMULATE_PREPARES      => false,
];
$pdo = new PDO($dsn, $user, $pass, $opt);

}

}

?>