看看PHP迭代器的内部执行过程
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";}
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:
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 [email protected]*/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";}
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: