<?php
class Animal {

}

$dog = new Animal();
$cat = new Animal();
$mouse = new Animal();

$spl = new SplObjectStorage();

$spl->attach($dog);
$spl->attach($cat);
$spl->attach($mouse);

foreach ($spl as $a) {
	echo "Outer start\n";
	
	foreach ($spl as $b) {
		echo "Inner\n";
	}
	
	echo "Outer end\n";
}