Return array of all classes implementing the Iterator Interface

gistfile.php

<?php

// Source: http://stackoverflow.com/questions/3993759/php-how-to-get-a-list-of-classes-that-implement-certain-interface

print_r(
    array_filter(
        get_declared_classes(), 
        function ($className) {
            return in_array('Iterator', class_implements($className));
        }
    )
);