php中的迭代器

<?php
class myIterator implements Iterator {
    private $position = 0;
    private $array = array(
        "firstelement",
        "secondelement",
        "lastelement",
    );  

    public function __construct() {
        $this->position = 0;
    }

    function rewind() {
       var_dump(__METHOD__);
        $this->position = 0;
    }

    function current() {
       var_dump(__METHOD__);
        return ‘one_‘ . $this->array[$this->position] . ‘_two‘;
    }

    function key() {
       var_dump(__METHOD__);
        return $this->position;
    }

    function next() {
        var_dump(__METHOD__);
        ++$this->position;
    }

    function valid() {
        var_dump(__METHOD__);
        return isset($this->array[$this->position]);
    }

}

$it = new myIterator;

foreach($it as $key => $value) {
    //var_dump($key,$value);
    echo $value;
    echo "\n";
}