$users = new \IMooc\AllUser();
foreach ($users as $user)
{
    var_dump($user);
}

<?php
namespace IMooc;

class AllUser implements \Iterator
{
    protected $ids;
    protected $data = array();
    protected $index;

    function __construct()
    {
        $db = new \IMooc\Database\MySQLi();
        $db->connect(‘127.0.0.1‘, ‘root‘, ‘root‘,‘test‘);
        $result = $db->query("select id from user");
        $this->ids = $result->fetch_all(MYSQLI_ASSOC);
    }
    //返回当前的数据
    function current()
    {
        $id = $this->ids[$this->index][‘id‘];
        return Factory::getUser($id);
    }

    //将索引值向下移动
    function next()
    {
        $this->index ++;
    }

    //查询当前是否有数据
    function valid()
    {
        return $this->index < count($this->ids);
    }

    //将迭代器移动到集合的开头
    function rewind()
    {
        $this->index = 0;
    }

    //返回当前key
    function key()
    {
        return $this->index;
    }
}

<?php
namespace IMooc;

class Factory
{
    static function getUser($id)
    {
        $key = ‘user_‘.$id;
        $user = Register::get($key);
        if (!$user)
        {
            $user = new User($id);
            Register::set($key, $user);
        }
        return $user;
    }
}