Question

This is how I’ve set up my Singleton

<?php
    class MySingleton
    {
        private static $instance;
        private static $you;

        private function __construct()
        {
            $this->you = "foo";     
        }

        public static function singleton()
        {
            if (!isset(self::$instance)) {              
                $className = __CLASS__;
                self::$instance = new $className;
            }
            return self::$instance;
        }

        public function getYou()
        {
            return $this->you;
        }       
        public function setYou($val)
        {
            $this->you = $val;
        }

    }
?>

In file1.php, I do this:

require_once('session.php');
$session = MySingleton::singleton();
$session->setYou('bar');
echo $session->getYou(); //echoes 'bar'

In file1.php, I have a hyperlink to file2.php, where I have this code:

require_once('session.php');
$session = MySingleton::singleton();
echo ($session->getYou()); //prints 'foo' which gets set in the constructor

It seems it is creating a new instance for file2, which is why $you has the default value of foo. Where am I going wrong? Why don’t I get the instance I was using in file1.php?

Answer 1

A singleton in PHP is only valid for the current request (as HTTP is stateless).

If you want to preserve the state of that object, save it in a session:

class MySingleton
    {
        private static $instance;
        private static $you;

        private function __construct()
        {
            $this->you = "foo";     
        }

        public static function singleton()
        {
            session_start();
            if (!($_SESSION['MyInstance'] instanceof MySingleton)) {              
                $className = __CLASS__;
                $_SESSION['MyInstance'] = new $className;
            }
            return $_SESSION['MyInstance'];
        }

        public function getYou()
        {
            return $this->you;
        }       
        public function setYou($val)
        {
            $this->you = $val;
        }

    }