以下我们来了解怎样实现一个自己定义的迭代器，然后再開始慢慢理解迭代器的内部工作原理。先来看一个官方的样例：

<?

php

class myIterator implements Iterator {

    private $position = 0;

    private $array = array(

        "first_element",

        "second_element",

        "last_element",

    );  

    public function __construct() {

        $this->position = 0;

    }

    function rewind() {

        var_dump(__METHOD__);

        $this->position = 0;

    }

    function current() {

        var_dump(__METHOD__);

        return $this->array[$this->position];

    }

    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) {

	echo '输出键值：';

    var_dump($key, $value);

	//echo $key;

    echo "\n";

}

程序执行输出：

string(18) "myIterator::rewind"

string(17) "myIterator::valid"

string(19) "myIterator::current"

string(15) "myIterator::key"

输出键值：int(0)

string(13) "first_element"

string(16) "myIterator::next"

string(17) "myIterator::valid"

string(19) "myIterator::current"

string(15) "myIterator::key"

输出键值：int(1)

string(14) "second_element"

string(16) "myIterator::next"

string(17) "myIterator::valid"

string(19) "myIterator::current"

string(15) "myIterator::key"

输出键值：int(2)

string(12) "last_element"

string(16) "myIterator::next"

string(17) "myIterator::valid"

一般的迭代器内部须要以下的方法：

• Iterator::current — Return the current element 返回当前元素
• Iterator::key — Return the key of the current element 返回当前元素的键
• Iterator::next — Move forward to next element 移向下一个元素
• Iterator::rewind — Rewind the Iterator to the first element 又一次回到第一个元素
• Iterator::valid — Checks if current position is valid 检查当前位置的有效性

假设不是非常清楚迭代器的内容工作流程。能够查看以下的迭代器对数组的遍历过程：

<?

php

/**

* @author nicesunboy@gmail.com

*/

class MyIterator implements Iterator

{

     private $var = array();

     public function __construct($array)

     {

         if (is_array($array)) {

            $this->var = $array;

         }

     }

     public function rewind() {

         echo "倒回第一个元素\n";

        reset($this->var);

     }

     public function current() {

        $var = current($this->var);

         echo "当前元素: $var\n";

         return $var;

     }

     public function key() {

        $var = key($this->var);

         echo "当前元素的键: $var\n";

         return $var;

     }

     public function next() {

        $var = next($this->var);

         echo "移向下一个元素: $var\n";

         return $var;

     }

     public function valid() {

        $var = $this->current() !== false;

         echo "检查有效性: {$var}\n";

         return $var;

     }

}

$values = array(1,2,3);

$it = new MyIterator($values);

foreach ($it as $k => $v) {

     print "此时键值对 -- key $k: value $v\n\n";

}

程序执行结果：

倒回第一个元素

当前元素: 1

检查有效性: 1

当前元素: 1

当前元素的键: 0

此时键值对 -- key 0: value 1

移向下一个元素: 2

当前元素: 2

检查有效性: 1

当前元素: 2

当前元素的键: 1

此时键值对 -- key 1: value 2

移向下一个元素: 3

当前元素: 3

检查有效性: 1

当前元素: 3

当前元素的键: 2

此时键值对 -- key 2: value 3

移向下一个元素:

当前元素:

检查有效性: 

今天，它是很清楚？