PersistentArray, an ArrayObject extension to maintain state in a JSON file (for running batch scripts etc.)

PersistentArray.php

<?php

/*
 * Example:
 *
 * $store = PersistentArray::load('example.json');
 * echo "Key is: " . (isset($store['key']) ? $store['key'] : 'not set') . "\n";
 * $store['key'] = '123';
 *
 * Running this twice will yield:
 * 
 * Key is: not set
 * Key is: 123
 * 
 */

class PersistentArray extends ArrayObject
{
    private $filename = null;

    public static function load ($filename)
    {
        if (file_exists($filename) && filesize($filename))
        {
            $data = json_decode(file_get_contents($filename), true);
        }
        else
        {
            $data = array();
            if (!touch($filename))
            {
                die("Could not create $filename");
            }
        }
        $created = new self($data);
        $created->filename = $filename;
        register_shutdown_function(array($created,'shutdown'));
        return $created;
    }

    public function shutdown ()
    {
        file_put_contents($this->filename, json_encode($this->getArrayCopy(), JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE));
    }
}