将对象放到session中形成单列模式

<?php
/*
燕十八 公益PHP培训    课堂地址:YY频道88354001   学习社区:www.zixue.it
	将对象放到SESSION中形成单列模式
*/
                //打开session
                session_start();
	final class CartTool{
		private static $cart = null;
		public static $items = array();
		//保护构造函数,防止new
		final protected function __construct(){
			$this->test = mt_rand(10,48);
		}
		private function __clone(){}
		//判断是否存在了对象
		protected function getIns(){
			if(!self::$cart instanceof self){
				self::$cart = new self;
			}
			return self::$cart;
		}
		//将对象放到session中形成单列模式
		public static function getCart(){
			if(!isset($_SESSION['cart']) || !($_SESSION['cart'] instanceof self)){
				$_SESSION['cart'] = self::getIns();
			}
			return $_SESSION['cart'];
		}