php聚合式迭代器是什么

class MainIterator implements Iterator

{

    private $var = array();

    public function __construct($array)    //构造函数, 初始化对象数组

    {

        if (is_array($array)) {

        $this->var = $array;

        }

    }

    public function rewind() {  

        echo "rewinding\n";

        reset($this->var);    //将数组的内部指针指向第一个单元

    }

    public function current() {

        $var = current($this->var);    // 返回数组中的当前值

        echo "current: $var\n";

        return $var;

    }

    public function key() {

        $var = key($this->var);       //返回数组中内部指针指向的当前单元的键名

        echo "key: $var\n";

        return $var;

    }

    public function next() {

        $var = next($this->var);     //返回数组内部指针指向的下一个单元的值

        echo "next: $var\n";

        return $var;

    }

    public function valid() {

    return !is_null(key($this->var); //判断当前单元的键是否为空

    }

}