php singleton registry

<?php

class Registry
{
    /**
     * Static instance
     *
     * @var Registry
     */
    private static $_instance;

    /**
     * Object hash map
     *
     * @var array
     */
    private $_map;

    /**
     * Private constructor
     *
     */
    private function __construct()
    {}

    /**
     * Get the single instance
     *
     * @return Registry
     */
    public static function getInstance()
    {
            if(self::$_instance === null)
            {
                    //First and only construction.
                    self::$_instance = new self();
            }
            return self::$_instance;
    }

    /**
     * Get an object by key
     *
     * @param string|int $key
     * @return object
     */
    public function get($key)
    {
            return $this->_map[$key];
    }

    /**
     * Set an object by key
     *
     * @param string|int $key
     */
    public function set($key, $object)
    {
            return $this->_map[$key] = $object;
    }

    /**
     * Disallow cloning
     *
     */
    private function __clone()
    {}
}

?>