<?php
class MyClass extends RecursiveIteratorIterator
{
    public function __construct()
    {
        parent::__construct(new MyClass_Letters);
    }
}

class MyClass_Letters extends RecursiveArrayIterator
{
	public function __construct()
	{
		parent::__construct(array('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
			'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
			'y', 'z'));
	}
	
	public function hasChildren()
	{
		return true;
	}
	
	public function getChildren()
	{
		return new MyClass_Things($this->current());
	}
}

class MyClass_Things extends RecursiveArrayIterator
{
    public function __construct($letter)
    {
        //do something with $letter and construct it self
        $array = array();

        parent::__construct($array);
    }
}

$obj = new MyClass;

foreach($obj as $entry){
   //I expect each iteration of _Things over each iteration of _Letters

   //It works. Is it a bad idea?
}
?>