README

sidebar_key	singleton-pattern
tags	php

Singleton Pattern

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

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👁 GitHub source
👁 GitHub license
👁 GitHub release

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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