File a.php

<?php
class a {
public function request($key, $default = '') {
return (isset($_REQUEST[$key])) ? $_REQUEST[$key] : $default;
}
}
?>

File b.php

<?php
class b {
const CONST_NAME = 'OK';
}
?>

File main.php

<?php
function __autoload($class_name) {
include_once $class_name . '.php';
}
class Foo {
public function bar() {
echo a::request('var', b::CONST_NAME);
}
}
$foo = new Foo;
$foo->bar();
?>