iterator.php

<?php

class TestIterator implements \IteratorAggregate
{
    public function getIterator()
    {
        return new ArrayIterator(array(1, 2, 3));
    }
}

class Test implements \IteratorAggregate
{

    public function getIterator()
    {
        return new TestIterator();
    }

}

foreach (new Test as $v) {
    echo $v;
}

// 123