Singleton Pattern

A lightweight PHP implementation of the Design Pattern Singleton using trait. Just one class and no dependencies.

Documentation

• Getting Started - Installation and requirements
• Creating a Singleton Class - How to implement the pattern
• Using Your Singleton - Working with singleton instances
• How It Works - Implementation details
• API Reference - Complete API documentation

Requirements

PHP 8.3 or higher

Installation

composer require "byjg/singleton-pattern"

Creating a Singleton Class

<?php
require "vendor/autoload.php";

class Example
{
    // Use the Singleton trait to implement the pattern
    use \ByJG\DesignPattern\Singleton;
    
    // You can add properties to your singleton
    public string $someProperty;
    
    // The constructor MUST be private or protected
    private function __construct()
    {
        // Optional initialization code
        $this->someProperty = "Initial value";
    }
    
    // Add your own methods and properties here
    public function doSomething(): void
    {
        // Your code here
    }
}

IMPORTANT:

1. Your class MUST use a private or protected constructor.
2. Singleton classes do not accept arguments in the constructor.
3. Attempting to clone, serialize, or unserialize a singleton will throw a SingletonException.

Using your Singleton class

// Get the singleton instance
$example = Example::getInstance();

// The same instance is always returned
$anotherReference = Example::getInstance();
$example->someProperty = "Changed value";

// This will output "Changed value" because both variables reference the same instance
echo $anotherReference->someProperty;

// This will throw a SingletonException
try {
    $cloned = clone $example;
} catch (\ByJG\DesignPattern\SingletonException $e) {
    echo "Cannot clone a singleton!";
}

How It Works

The Singleton trait:

• Implements the getInstance() static method to create and manage a single instance
• Prevents cloning by overriding the __clone() method
• Prevents serialization and deserialization by overriding __sleep() and __wakeup()
• Uses a static local variable within getInstance() to store instances of each class that uses the trait

Run Tests

vendor/bin/phpunit

References

• Wikipedia: Singleton Pattern
• Documentation

Dependencies

flowchart TD
    byjg/singleton-pattern

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Open source ByJG