読めるけど書けない

Niigata.php

<?php
/**
 * Niigata Class
 *
 * @author  Keisuke SATO aka riaf <[email protected]>
 * @license New BSD License
 **/
class Niigata
{
    protected $_niigata_ = array();

    public function __get($name) {
        if (isset($this->_niigata_[$name])) {
            return $this->_niigata_[$name];
        }
        $class = get_class($this);
        trigger_error("Undefined property: $class::\$$name", E_USER_NOTICE);
    }

    public function __isset($name) {
        return isset($this->_niigata_[$name]);
    }

    public function __set($name, $value) {
        $d = debug_backtrace();
        if (isset($d[1]) && isset($d[1]['class']) && is_subclass_of($d[1]['class'], __CLASS__)) {
            $this->_niigata_[$name] = $value;
        } else {
            $class = get_class($this);
            trigger_error("Cannot access niigata property $class::\$$name", E_USER_WARNING);
        }
    }
}