<?php
class misc_class { 
  public  $var1 = "abc";
  public  $var2 = 123;
  public  $var3 = "def";
  private $var4 = 456;
}
$test = new misc_class;
foreach($test as $key=>$value)
  echo "$key = $value<br />\n";
?>
Output
var1 = abc
var2 = 123
var3 = def
You can overload PHP's internal iterator by redefining the rewind(), current(), key(), next() and valid() methods like this: 

<?php
class MyIterator implements Iterator {
   private $var = array();

   public function __construct($array) {
       if (is_array($array)) {
           $this->var = $array;
       }
   }
   public function rewind() {
       echo "rewinding<br />\n";
       reset($this->var);
   }
   public function current() {
       $var = current($this->var);
       echo "current: $var<br />\n";
       return $var;
   }
   public function key() {
       $var = key($this->var);
       echo "key: $var<br />\n";
       return $var;
   }
   public function next() {
       $var = next($this->var);
       echo "next: $var<br />\n";
       return $var;
   }
   public function valid() {
       $var = $this->current() !== false;
       echo "valid: {$var}<br />\n";
       return $var;
   }
}

$it = new MyIterator(array(1,2,3));
foreach ($it as $key=>$value) {
   echo "$key: $value<br />\n";
}
?>
Output
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:
If you just want to override some of them, use the IteratorAggregate class.