<?php
class Example
{
// Hold an instance of the class
private static $instance;
// A private constructor; prevents direct creation of object
private function __construct()
{
echo 'I am constructed';
}
// The singleton method
public static function singleton()
{
if (!isset(self::$instance)) {
$c = __CLASS__;
self::$instance = new $c;
}
return self::$instance;
}
// Example method
public function bark()
{
echo 'Woof!';
}
// Prevent users to clone the instance
public function __clone()
{
trigger_error('Clone is not allowed.', E_USER_ERROR);
}
}
?>
This allows a single instance of the Example
class to be retrieved.
<?php
// This would fail because the constructor is private
$test = new Example;
// This will always retrieve a single instance of the class
$test = Example::singleton();
$test->bark();
// This will issue an E_USER_ERROR.
$test_clone = clone $test;
?>
Load balance : Server 04
