PHP面试题之设计模式

/**
 * 单例模式
 * 
 */
class Config
{
    static private $_instance = NULL;
    private $_settings = array();
    private function __construct(){}
    private function __clone(){};

    static function getInstance()
    {
        if(self::$_intance == NULL){
            self::$_intance = new Config();
        }
        return self:$_intance;
    }

    public function set($index,$value)
    {
        $this->_setting[$index] = $value;
    }

    public function get($index)
    {
        return $this->_settings[$index];
    }
}