How to make objects in PHP perform foreach loop like arrays

How to make objects in PHP perform foreach loop like arrays_PHP Tutorial

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Release： 2016-07-21 14:59:42

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When I first came across the problem, I didn’t consider the Iterator mode. I tried a few general ideas and failed. . . . I went directly to look at the source code implementation of foreach, hoping to find out whether there are any special features when foreach handles objects, which can be used as a breakthrough.

After tracking for a long time, I found a strange switch in the core logic:

Copy the code The code is as follows:

 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;
}

From this structure, we can see that the objects are divided into ZEND_ITER_OBJECT and ZEND_ITER_PLAIN_OBJECT. What does this mean?

Copy code The code is as follows:

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;                                                      ;
 }
 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;
     }
}


This Let’s talk about PHP’s built-in interface Iterator. PHP5 starts to support the interface and has a built-in Iterator interface. So if you define a class and implement the Iterator interface, then your class object is ZEND_ITER_OBJECT, otherwise it is ZEND_ITER_PLAIN_OBJECT. 


For the ZEND_ITER_PLAIN_OBJECT class, foreach will obtain the default attribute array of the object through HASH_OF, and then perform foreach on the array.

For ZEND_ITER_OBJECT class objects, foreach will be performed by calling the Iterator interface related functions implemented by the object. Iterator interface:

Copy code

The code is as follows :Iterator extends Traversable {/* method*/

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 )
}

So, for this written test question, you can give the following answer:

Copy the code The code is as follows:

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;
}

The above code runs normally under my php 5.3.