switch (zend_iterator_unwrap(array, &iter TSRMLS_CC)) {
        default:
        case ZEND_ITER_INVALID:
               .....
               break
        case ZEND_ITER_PLAIN_OBJECT: {
                ......
            break;
     case ZEND_ITER_PLAIN_ARRAY:
            .....
            break;
        case ZEND_ITER_OBJECT:
            ......
            break;
}

從這個(gè)結(jié)構(gòu)，我們可以看到，對(duì)象分為ZEND_ITER_OBJECT和ZEND_ITER_PLAIN_OBJECT, 這是什么意思呢？

復(fù)制代碼代碼如下:

ZEND_API enum zend_object_iterator_kind zend_iterator_unwrap(
    zval *array_ptr, zend_object_iterator **iter TSRMLS_DC)
{
    switch (Z_TYPE_P(array_ptr)) {
        case IS_OBJECT:
            if (Z_OBJ_HT_P(array_ptr) == &iterator_object_handlers) {
                *iter = (zend_object_iterator *)zend_object_store_get_object(array_ptr TSRMLS_CC);
                return ZEND_ITER_OBJECT;
            }
            if (HASH_OF(array_ptr)) {
                return ZEND_ITER_PLAIN_OBJECT;
            }
            return ZEND_ITER_INVALID;
        case IS_ARRAY:
            if (HASH_OF(array_ptr)) {
                return ZEND_ITER_PLAIN_ARRAY;
            }
            return ZEND_ITER_INVALID;
        default:
            return ZEND_ITER_INVALID;
    }
}

這就要講到PHP的內(nèi)置接口Iterator了，PHP5開始支持了接口，并且內(nèi)置了Iterator接口，所以如果你定義了一個(gè)類，并實(shí)現(xiàn)了Iterator接口，那么你的這個(gè)類對(duì)象就是ZEND_ITER_OBJECT,否則就是ZEND_ITER_PLAIN_OBJECT.

對(duì)于ZEND_ITER_PLAIN_OBJECT的類，foreach會(huì)通過HASH_OF獲取該對(duì)象的默認(rèn)屬性數(shù)組，然后對(duì)該數(shù)組進(jìn)行foreach.

而對(duì)于ZEND_ITER_OBJECT的類對(duì)象，則會(huì)通過調(diào)用對(duì)象實(shí)現(xiàn)的Iterator接口相關(guān)函數(shù)來進(jìn)行foreach，iterator接口：

復(fù)制代碼代碼如下:

Iterator extends Traversable {
/* 方法 */
abstract public mixed current ( void )
abstract public scalar key ( void )
abstract public void next ( void )
abstract public void rewind ( void )
abstract public boolean valid ( void )
}

所以，對(duì)于這道筆試題，可以作出如下的答案：

復(fù)制代碼代碼如下:

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