PHP内置接口Iterator

PHP的内置接口Iterator了，PHP5开始支持了接口， 并且内置了Iterator接口， 所以如果你定义了一个类，并实现了Iterator接口，那么你的这个类对象就是ZEND_ITER_OBJECT,否则就是ZEND_ITER_PLAIN_OBJECT.

对于ZEND_ITER_PLAIN_OBJECT的类，foreach会通过HASH_OF获取该对象的默认属性数组，然后对该数组进行foreach.
而对于ZEND_ITER_OBJECT的类对象，则会通过调用对象实现的Iterator接口相关函数来进行foreach， 所以， 对于这道笔试题， 可以作出如下的答案：

1. class sample implements Iterator
2. {
3.     private $_items = array(1,2,3,4,5,6,7);
4.  
5.     public function __construct() {
6.                   ;//void
7.     }
8.     public function rewind() { reset($this->_items); }
9.     public function current() { return current($this->_items); }
10.     public function key() { return key($this->_items); }
11.     public function next() { return next($this->_items); }
12.     public function valid() { return ( $this->current() !== false ); }
13. }
14.  
15. $sa = new sample();
16. foreach($sa as $key => $val){
17.     print $key . "=>" .$val;
18. }