An iterator example which provides a memory efficient way of handling arrays of objects.

TrainsIterator.php

<?php 

class Trains implements Iterator
{
    protected $objectIds;
    private $idx = 0;
    
    public function __construct($objectIds)
    {
        $this->objectIds = $objectIds;
    }
    
    public function current()
    {
        return new Model_Train($objectIds[$this->idx]);
    }
    
    public function rewind()
    {
        $this->idx = 0;
    }
    
    public function key()
    {
        return $this->idx;
    }
    
    public function next()
    {
        ++$this->idx;
    }
    
    public function valid()
    {
        return isset($this->objectIds[$this->idx]);
    }
}


$myTrains = new Trains(array(1,2,3));
foreach ($myTrains as $train)
{
    // $train is Model_Train instance
}