看看PHP迭代器的内部执行过程

来源：互联网发布：京都议定书知乎编辑：程序博客网时间：2024/04/29 17:21

下面我们来了解如何实现一个自定义的迭代器，然后再开始慢慢理解迭代器的内部工作原理。先来看一个官方的例子：

<?phpclass 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";}

程序运行输出：

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"

一般的迭代器内部需要下面的方法：

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 重新回到第一个元素
Iterator::valid — Checks if current position is valid 检查当前位置的有效性

如果不是很清楚迭代器的内容工作流程，可以查看下面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";}

程序运行结果：

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:

现在就很清晰了吧？

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