Example of Singleton Pattern in PHP

A guide on the Singleton Pattern in PHP with a detailed example, explaining how to implement and use this design pattern in object-oriented programming.

The Singleton pattern ensures that only one instance of a class is created during the program’s runtime. It is often used for managing shared resources such as database connections.

<?php
// Singleton Pattern in PHP

class Singleton {
    // Property to store the single instance of the class
    private static $instance = null;

    // Private constructor to prevent instantiation from outside the class
    private function __construct() {
        echo "Instance created.\n";
    }

    // Prevent cloning of the instance
    private function __clone() {}

    // Prevent unserialization of the instance
    private function __wakeup() {}

    // Method to get the single instance of the class
    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new Singleton();
        }
        return self::$instance;
    }

    // A simple method to demonstrate functionality
    public function doSomething() {
        echo "Doing something from the Singleton instance.\n";
    }
}

// Retrieve the Singleton instance
$singleton1 = Singleton::getInstance();
$singleton1->doSomething();

// Attempt to get another instance
$singleton2 = Singleton::getInstance();
$singleton2->doSomething();

// Check if both instances are the same object
var_dump($singleton1 === $singleton2);  // Output: true
?>

Detailed explanation:

1. private static $instance = null;: This property holds the single instance of the Singleton class. Initially, it's set to null.

2. private function __construct();: The constructor is made private to prevent creating new instances from outside the class.

3. private function __clone(); and private function __wakeup();: These methods prevent cloning or unserializing the object to avoid multiple instances.

4. public static function getInstance();: This is the core method of the Singleton pattern. It checks if the instance has been created. If not, it creates and stores the instance. If it exists, it returns the existing instance.

5. doSomething();: This method demonstrates an action that the Singleton instance can perform.

6. $singleton1 === $singleton2;: This comparison checks whether both instances are the same object. The result is true, proving that only one instance is created.

PHP Version:

This code is compatible with PHP 5.0 and above.