Trait for Singleton Pattern for PHP

Singleton.php

<?php

trait Singleton
{
    /**
     * Stores the instance, implementing a Singleton pattern.
     *
     * @var self
     */
    private static self $instance;

    /**
     * The Singleton's constructor should always be private to prevent direct
     * construction calls with the `new` operator.
     */
    final private function __construct() {}

    /**
     * Singletons should not be cloneable.
     */
    final private function __clone() {}

    /**
     * Singletons should not be restorable from strings.
     *
     * @throws Exception Cannot unserialize a singleton.
     */
    final public function __wakeup() {
        throw new \Exception('Cannot unserialize a singleton.');
    }

    /**
     * This is the static method that controls the access to the singleton
     * instance. On the first run, it creates a singleton object and places it
     * into the static property. On subsequent runs, it returns the client existing
     * object stored in the static property.
     *
     * @return self
     */
    final public static function getInstance(): self
    {
        if (! isset(self::$instance)) {
            self::$instance = new self();
        }

        return self::$instance;
    }
}