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
class MyClass
{
public $var1 = 1;
public $var2 = 2;
public $var3 = 3;
protected $protected = 'protected var';
private $private = 'private var';
function iterateVisible(){
echo "MyClass::iterateVisible:<br>";
foreach($this as $key => $value){
print "$key=>$value<br>";
}
}
}
$class = new MyClass();
foreach($class as $key => $value){
print "$key => $value<br>";
}
echo "<br>";
$class->iterateVisible();输出结果：
var1 => 1
var2 => 2
var3 => 3
MyClass::iterateVisible:
var1=>1
var2=>2
var3=>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。
class MyIterator implements Iterator{
private $var = array();
public function __construct($array)
{
if(is_array($array)){
$this->var = $array;
}
}
public function rewind(){
echo "rewinding<br>";
reset($this->var);
}
public function current(){
$var = current($this->var);
echo "current:$var<br>";
return $var;
}
public function key(){
$var = key($this->var);
echo "key:$var<br>";
return $var;
}
public function next(){
$var = next($this->var);
echo "next:$var<br>";
return $var;
}
public function valid(){
$var = $this->current()!==false;
echo "valid:$var<br>";
return $var;
}
}
$values = array(1,2,3);
$it = new MyIterator($values);
foreach($it as $a => $b){
print "$a:$b<br>";
}输出结果：
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
include_once('class2.php');
class MyCollection implements IteratorAggregate
{
private $items = array();
private $count = 0;
public function getIterator(){
return new MyIterator($this->items);
}
public function add($value){
$this->items[$this->count++] = $value;
}
}
$coll = new MyCollection();
$coll -> add('1');
$coll -> add('2');
$coll -> add('3');
foreach($coll as $k => $v){
echo "key/value:[$k->$v]<br><br>";
}输出结果：
rewinding
current:1
valid:1
current:1
key:0
key/value:[0->1]
next:2
current:2
valid:1
current:2
key:1
key/value:[1->2]
next:3
current:3
valid:1
current:3
key:2
key/value:[2->3]
next:
current:
valid:
