Laravel学习笔记之PHP对象遍历(Iterator)
说明：本文章主要讲述PHP的对象遍历(Iterator)知识点。由于Laravel框架中就在集合(Collection)中用到了对象遍历知识点，故记录并学习之。同时，作者会将开发过程中的一些截图和代码黏上去，提高阅读效率。
Laravel中在基础集合类Illuminate\Support\Collection、路由类中Illuminate\Routing\RouteCollection和分页类中Illuminate\Pagination\Paginator等，都用到了对象遍历这个小知识点，这些类都是实现了IteratorAggregate这个接口，这个接口定义getIterator()，返回的是迭代器对象。PHP标准扩展库中提供了很多默认迭代器实现类，比较常用的是数组迭代器对象ArrayIterator，参考官网：迭代器。
对象遍历(Iterator)
基本遍历
PHP5提供了遍历对象属性的方法，而且默认是可见属性，如代码中foreach遍历对象属性，默认的都是可见属性：
$value) { echo $key.':'.$value.PHP_EOL;}输出的是：
name:PHPaddress:php.net如果需要遍历对象的不可见属性，则在对象内部定义一个遍历方法：
public function unAccessIterator() { echo 'Iterator the unaccess fields:'.PHP_EOL; foreach ($this as $key => $value) { echo $key.':'.$value.PHP_EOL; } }对象外部访问：
$testIterator->unAccessIterator();将可以遍历对象的不可见属性，输出结果：
Iterator the unaccess fields:name:PHPaddress:php.netsex:manage:20Iterator接口
PHP提供了Iterator接口，用来定义迭代器对象来自定义遍历，所以利用Iterator接口来构造迭代器，需要实现Iterator定义的几个方法：
composerPackage = $composerPackage; } public function unAccessIterator() { echo 'Iterator the unaccess fields:'.PHP_EOL; foreach ($this as $key => $value) { echo $key.':'.$value.PHP_EOL; } } / * Return the current element * @link http://php.net/manual/en/iterator.current.php * @return mixed Can return any type. * @since 5.0.0 */ public function current() { // TODO: Implement current() method. echo 'Return the current element:'.PHP_EOL; return current($this->composerPackage); } / * Move forward to next element * @link http://php.net/manual/en/iterator.next.php * @return void Any returned value is ignored. * @since 5.0.0 */ public function next() { // TODO: Implement next() method. echo 'Move forward to next element:'.PHP_EOL; return next($this->composerPackage); } / * Return the key of the current element * @link http://php.net/manual/en/iterator.key.php * @return mixed scalar on success, or null on failure. * @since 5.0.0 */ public function key() { // TODO: Implement key() method. echo 'Return the key of the current element:'.PHP_EOL; return key($this->composerPackage); } / * Checks if current position is valid * @link http://php.net/manual/en/iterator.valid.php * @return boolean The return value will be casted to boolean and then evaluated. * Returns true on success or false on failure. * @since 5.0.0 */ public function valid() { // TODO: Implement valid() method. echo 'Checks if current position is valid:'.PHP_EOL; return current($this->composerPackage) !== false; } / * Rewind the Iterator to the first element * @link http://php.net/manual/en/iterator.rewind.php * @return void Any returned value is ignored. * @since 5.0.0 */ public function rewind() { // TODO: Implement rewind() method. echo 'Rewind the Iterator to the first element:'.PHP_EOL; reset($this->composerPackage); }}/*$testIterator = new TestIterator();foreach ($testIterator as $key => $value) { echo $key.':'.$value.PHP_EOL;}$testIterator->unAccessIterator();*/$testIterator = new TestIterator([ 'symfony/http-foundation', 'symfony/http-kernel', 'guzzle/guzzle', 'monolog/monolog']);foreach ($testIterator as $key => $value) { echo $key.':'.$value.PHP_EOL;}成员变量$composerPackage是不可见的，通过实现Iterator接口，同样可以遍历自定义的可不见属性，输出结果如下：
Rewind the Iterator to the first element:Checks if current position is valid:Return the current element:Return the key of the current element:0:symfony/http-foundationMove forward to next element:Checks if current position is valid:Return the current element:Return the key of the current element:1:symfony/http-kernelMove forward to next element:Checks if current position is valid:Return the current element:Return the key of the current element:2:guzzle/guzzleMove forward to next element:Checks if current position is valid:Return the current element:Return the key of the current element:3:monolog/monologMove forward to next element:Checks if current position is valid:IteratorAggregate接口
PHP真心为程序员考虑了很多，实现IteratorAggragate接口后只需实现getIterator()方法直接返回迭代器对象，就不需要实现Iterator接口需要的一些方法来创建一些迭代器对象，因为PHP已经提供了很多迭代器对象如ArrayIterator对象。所以再重构下上面代码：
class TestCollection implements IteratorAggregate{ ... / * @var array */ private $composerPackage; ... / * Retrieve an external iterator * @link http://php.net/manual/en/iteratoraggregate.getiterator.php * @return Traversable An instance of an object implementing Iterator or * Traversable * @since 5.0.0 */ public function getIterator() { // TODO: Implement getIterator() method. return new ArrayIterator($this->composerPackage); }}$testCollection = new TestCollection([ 'symfony/http-foundation', 'symfony/http-kernel', 'guzzle/guzzle', 'monolog/monolog']);foreach ($testCollection as $key => $value) { echo $key.':'.$value.PHP_EOL;}同样的，能遍历$testCollection对象的不可见属性$composerPackage，输出结果：
0:symfony/http-foundation1:symfony/http-kernel2:guzzle/guzzle3:monolog/monolog文章开头聊到Laravel中就用到了IteratorAggragate这个接口，可以看看文件的源码。
总结：PHP提供的对象遍历特性功能还是很有用处的，下一篇准备看下generator生成器知识点，generator提供了另外一种方式定义Iterator。多多使用Laravel，研究Laravel源码并模仿之，也不错哦。
关键字：php, laravel, iterator
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