A PHP class to access a PHP array via dot notation

Config.php

<?php

namespace Treffynnon;

/**
 * A PHP class to access a PHP array via dot notation
 * (Agavi http://www.agavi.org was the inspiration).
 *
 * This was hacked in to an existing codebase hence the
 * global config array variable.
 *
 * The global $config variable should be an associative array like:
 * $config = array(
 *      'database' => array(
 *          'host' => 'localhost',
 *          'user' => 'Treffynnon',
 *          'pass' => 'password',
 *          'db'   => 'database',
 *      ),
 * );
 *
 * But it can be as deeply nested as you like. An example of how
 * to access the values  for the example config array above is
 * given below.
 *
 * @example $host = Config::get('database.host');
 * @author Simon Holywell
 */
class Config {

    /**
     * Get a particular value back from the config array
     * @global array $config The config array defined in the config files
     * @param string $index The index to fetch in dot notation
     * @param string $default If the requested index/value does not exist then the default value (as long as it is not null) will be returned
     * @return mixed
     */
    public static function get($index, $default = null) {
        global $config;
        $index = explode('.', $index);
        try {
            $return = self::getValue($index, $config);
        } catch (ConfigException $e) {
            if(!is_null($default)) {
                $return = $default;
            } else {
                throw $e;
            }
        }
        return $return;
    }

    /**
     * Navigate through a config array looking for a particular index
     * @param array $index The index sequence we are navigating down
     * @param array $value The portion of the config array to process
     * @return mixed
     */
    protected static function getValue($index, $value) {
        if(is_array($index) and
           count($index)) {
            $current_index = array_shift($index);
        }
        if(is_array($index) and
           count($index) and
           isset($value[$current_index]) and
           is_array($value[$current_index]) and
           count($value[$current_index])) {
            return self::getValue($index, $value[$current_index]);
        } elseif(isset($value[$current_index])) {
            return $value[$current_index];
        } else {
            throw new ConfigException("Attempt to access missing configuration variable: $current_index");
        }
    }
}
class ConfigException extends Exception {}

example.php

<?php
require_once 'classes/Config.php';

// this is a completely contrived example
$config = array(
    'site' => array(
        'title'       => 'Treffynnon',
        'description' => 'an exciting package',
        'keywords'    => 'exciting, demo, example, package',
        'author'      => array(
            'name'  => array(
                'title'  => 'Mr.',
                'first'  => 'Simon',
                'second' => 'Holywell'
            ),
            'email' => 'example@example.org',
        ),
    ),
    'database' => array(
        'host'     => 'localhost',
        'database' => 'my_database_name',
        'username' => 'my_database_username',
        'password' => 'my_database_password',
    ),
    'version' => '0.0.2',
);

$title = Config::get('site.author.name.title');
$second_name = Config::get('site.author.name.second');
$last_name = Config::get('site.author.name.last', 'Holywell'); // Example of setting a default for non-existent values
$email = Config::get('site.author.email');
?>

<p>To email <?php echo $title; ?> <?php echo $second_name; ?> <?php echo $last_name; ?> please click
    <a href="mailto:<?php echo $email; ?>">here</a>.</p>

I just made a super ambitious version of this, as a array object class I call 'Tree' but it turned out to have massive memory leak issues. I now going to rewrite it with a more simple approach like yours!