PHP 5 提供了一种定义对象的方法使其可以通过单元列表来遍历，例如用 foreach 语句。默认情况下，所有可见属性都将被用于遍历。
Example #1 简单的对象遍历
<?php
class MyClass
{
public $var1 = ‘value 1‘ ;
public $var2 = ‘value 2‘ ;
public $var3 = ‘value 3‘ ;
protected $protected = ‘protected var‘ ;
private $private = ‘private var‘ ;
function iterateVisible () {
echo "MyClass::iterateVisible:\n" ;
foreach( $this as $key => $value ) {
print " $key => $value \n" ;
}
}
}
$class = new MyClass ();
foreach( $class as $key => $value ) {
print " $key => $value \n" ;
}
echo "\n" ;
$class -> iterateVisible ();
?>
以上例程会输出：
var1 => value 1 var2 => value 2 var3 => value 3MyClass::iterateVisible: var1 => value 1 var2 => value 2 var3 => value 3 protected => protected var private => private var
如上所示，foreach 遍历了所有其能够访问的可见属性。
更进一步，可以实现 Iterator 接口。可以让对象自行决定如何遍历以及每次遍历时那些值可用。
Example #2 实现 Iterator 接口的对象遍历
<?php
class MyIterator implements Iterator
{
private $var = array();
public function __construct ( $array )
{
if ( is_array ( $array )) {
$this -> var = $array ;
}
}
public function rewind () {
echo "rewinding\n" ;
reset ( $this -> var );
}
public function current () {
$var = current ( $this -> var );
echo "current: $var \n" ;
return $var ;
}
public function key () {
$var = key ( $this -> var );
echo "key: $var \n" ;
return $var ;
}
public function next () {
$var = next ( $this -> var );
echo "next: $var \n" ;
return $var ;
}
public function valid () {
$var = $this -> current () !== false ;
echo "valid: { $var } \n" ;
return $var ;
}
}
$values = array( 1 , 2 , 3 );
$it = new MyIterator ( $values );
foreach ( $it as $a => $b ) {
print " $a : $b \n" ;
}
?>
以上例程会输出：
rewinding current: 1 valid: 1 current: 1 key: 0 0: 1 next: 2 current: 2 valid: 1 current: 2 key: 1 1: 2 next: 3 current: 3 valid: 1 current: 3 key: 2 2: 3 next: current: valid:
可以用 IteratorAggregate 接口以替代实现所有的 Iterator 方法。 IteratorAggregate 只需要实现一个方法 IteratorAggregate::getIterator() ，其应返回一个实现了 Iterator 的类的实例。
Example #3 通过实现 IteratorAggregate 来遍历对象
<?php
class MyCollection implements IteratorAggregate
{
private $items = array();
private $count = 0 ;
// Required definition of interface IteratorAggregate
public function getIterator () {
return new MyIterator ( $this -> items );
}
public function add ( $value ) {
$this -> items [ $this -> count ++] = $value ;
}
}
$coll = new MyCollection ();
$coll -> add ( ‘value 1‘ );
$coll -> add ( ‘value 2‘ );
$coll -> add ( ‘value 3‘ );
foreach ( $coll as $key => $val ) {
echo "key/value: [ $key -> $val ]\n\n" ;
}
?>
以上例程会输出：
rewinding current: value 1 valid: 1 current: value 1 key: 0 key/value: [0 -> value 1]next: value 2 current: value 2 valid: 1 current: value 2 key: 1 key/value: [1 -> value 2]next: value 3 current: value 3 valid: 1 current: value 3 key: 2 key/value: [2 -> value 3]next: current: valid: