<?php
/**
 * @copyright Copyright (C) 2006-2016 Xue Can <xuecan@gmail.com> and contributors.
 */

namespace Singleton;

/**
 * Singleton Design Pattern
 *
 * THIS IS CONSIDERED TO BE AN ANTI-PATTERN!
 * FOR BETTER TESTABILITY AND MAINTAINABILITY USE DEPENDENCY INJECTION!
 *
 * @author Xue Can <xuecan@netpas.co>
 */
class Singleton
{
    /**
     * @var Singleton[] The reference to *Singleton* instances of any child class.
     */
    private static $instances = [];

    /**
     * Returns the *Singleton* instance of this class.
     *
     * @return static The *Singleton* instance.
     */
    public static function getInstance()
    {
        if (!isset(self::$instances[static::class])) {
            self::$instances[static::class] = new static();
        }
        return self::$instances[static::class];
    }

    /**
     * Protected constructor to prevent creating a new instance of the
     * *Singleton* via the `new` operator from outside of this class.
     */
    protected function __construct()
    {
    }

    /**
     * Private clone method to prevent cloning of the instance of the
     * *Singleton* instance.
     *
     * @return void
     */
    final private function __clone()
    {
    }

    /**
     * Private unserialize method to prevent unserializing of the *Singleton*
     * instance.
     *
     * @return void
     */
    final private function __wakeup()
    {
    }

}