TypedList.php

<?php

function loader($class) {
    if (strpos($class, 'List') !== false) {
       eval("class $class extends TypedList {}");
    }
}
spl_autoload_register('loader');

abstract class TypedList extends ArrayObject
{
    public function __construct()
    {
        $type = str_replace('List', '', get_class($this));
        echo 'I am only going to accept ' . $type;
    }
}

$a = new BlahList;