API Reference

Singleton Trait

Namespace: ByJG\DesignPattern

The Singleton trait provides a complete implementation of the Singleton design pattern.

Methods

getInstance()

public static function getInstance(): static

Returns the singleton instance of the class. Creates the instance on first call.

Returns: The singleton instance of the calling class

Example:

$instance = MyClass::getInstance();

__construct()

protected function __construct()

Protected constructor to prevent direct instantiation. Override this in your class with a private or protected constructor.

Note: Should be overridden as private or protected in implementing classes.

__clone()

public function __clone()

Prevents cloning of the singleton instance.

Throws: ByJG\DesignPattern\SingletonException - Always throws when clone is attempted

Example:

try {
    $cloned = clone $instance;
} catch (\ByJG\DesignPattern\SingletonException $e) {
    // Handle exception
}

__sleep()

public function __sleep()

Prevents serialization of the singleton instance.

Throws: ByJG\DesignPattern\SingletonException - Always throws when serialization is attempted

Example:

try {
    $serialized = serialize($instance);
} catch (\ByJG\DesignPattern\SingletonException $e) {
    // Handle exception
}

__wakeup()

public function __wakeup()

Prevents unserialization of the singleton instance.

Throws: ByJG\DesignPattern\SingletonException - Always throws when unserialization is attempted

Example:

try {
    $instance = unserialize($data);
} catch (\ByJG\DesignPattern\SingletonException $e) {
    // Handle exception
}

SingletonException

Namespace: ByJG\DesignPattern Extends: Exception

Exception thrown when attempting prohibited operations on a singleton instance.

When It's Thrown

This exception is thrown in the following scenarios:

1. Cloning attempt - When trying to clone a singleton instance
2. Serialization attempt - When trying to serialize a singleton instance
3. Unserialization attempt - When trying to unserialize a singleton instance

Properties

Inherits all properties from the standard PHP Exception class:

• $message - The exception message
• $code - The exception code
• $file - The filename where the exception was thrown
• $line - The line number where the exception was thrown

Example

use ByJG\DesignPattern\SingletonException;

try {
    $cloned = clone MyClass::getInstance();
} catch (SingletonException $e) {
    echo "Error: " . $e->getMessage();
    // Output: Error: You can not clone a singleton.
}

Usage Example

Complete example showing all API features:

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

use ByJG\DesignPattern\Singleton;
use ByJG\DesignPattern\SingletonException;

class Logger
{
    use Singleton;

    private array $logs = [];

    private function __construct()
    {
        // Initialize logger
    }

    public function log(string $message): void
    {
        $this->logs[] = [
            'time' => time(),
            'message' => $message
        ];
    }

    public function getLogs(): array
    {
        return $this->logs;
    }
}

// Get instance
$logger = Logger::getInstance();
$logger->log("Application started");

// Same instance is returned
$sameLogger = Logger::getInstance();
echo count($sameLogger->getLogs()); // Output: 1

// These operations throw SingletonException:
try {
    clone $logger;
} catch (SingletonException $e) {
    echo $e->getMessage(); // You can not clone a singleton.
}

try {
    serialize($logger);
} catch (SingletonException $e) {
    echo $e->getMessage(); // You can not serialize a singleton.
}

Type Safety

The trait uses the static return type for getInstance(), which provides proper type hinting in IDEs:

// IDE knows $logger is of type Logger, not just Singleton
$logger = Logger::getInstance();
$logger->log("test"); // IDE autocomplete works correctly