单例模式

<?php

class Singleton
{
    private static $_instance;

    /**
     * 构造函数私有，不允许在外部实例化
     */
    private function __construct()
    {

    }

    /**
     * 防止对象实例被克隆
     */
    private function __clone()
    {

    }

    /**
     * 防止被反序列化
     */
    private function __wakeup()
    {

    }

    public static function getInstance()
    {
        if (!self::$_instance instanceof self) {
            self::$_instance = new Singleton();
        }

        return self::$_instance;
    }

    public function test()
    {
        echo "This is test";
    }
}


$a = Singleton::getInstance();

echo gettype($a);
echo "<br/>";
$a->test();

// $b = clone $a;
// $c = new Singleton();
 
$d = serialize($a);
$e = unserialize($d);