class AppConfig { private static $instance; private $settings = []; private function __construct() { // load configuration settings from file or database $this->settings = [ 'db_host' => 'localhost', 'db_name' => 'mydb', 'db_user' => 'root', 'db_pass' => 'password' ]; } public static function getInstance(): AppConfig { if (self::$instance === null) { self::$instance = new AppConfig(); } return self::$instance; } public function getSetting(string $key): ?string { return $this->settings[$key] ?? null; } }
class Logger { private static $instance; private $messages = []; private function __construct() { // initialize the logger } public static function getInstance(): Logger { if (self::$instance === null) { self::$instance = new Logger(); } return self::$instance; } public function log(string $message) { $this->messages[] = $message; } public function getLogs(): array { return $this->messages; } }In this case, the `Logger` class has a private constructor and a static method `getInstance` that returns the single instance of the class. The `log` method allows adding a message to the logger, and the `getLogs` method returns all logged messages as an array. The PHP package library that implements the singleton pattern is not a specific one, as this design pattern is a language construct. However, some PHP frameworks, such as Laravel, provide built-in support for singleton classes through the dependency injection container.