<?php

use \Exception;

class Singleton

{

    /**

     * 对象实例

     * @var object

     /

    public static $instance;

    /**

     * 获取实例化对象

     /

    public static function getInstance()

    {

        if (!self::$instance instanceof self) {

            self::$instance = new self();

        }

        return self::$instance;

    }

    /**

     * 禁止对象直接在外部实例

     /

    private function __construct(){}

    /**

     * 防止克隆操作

     /

    final public function __clone()

    {

        throw new Exception('Clone is not allowed !');

    }

}

// SingletonFacotry.php

<?php

use \Exception;

abstract class SingletonFacotry

{

    /**

     * 对象实例数组

     * @var array

     /

    protected static $instance = [];

    /**

     * 获取实例化对象

     /

    public static function getInstance()

    {

        $callClass = static::getInstanceAccessor();

        if (!array_key_exists($callClass, self::$instance)) {

            self::$instance[$callClass] = new $callClass();

        }

        return self::$instance[$callClass];

    }

    abstract protected static function getInstanceAccessor();

    /**

     * 禁止对象直接在外部实例

     /

    protected function __construct(){}  

    /**

     * 防止克隆操作

     /

    final public function __clone()

    {

         throw new Exception('Clone is not allowed !');

    }

}

// A.php

<?php

class A extends SingletonFactory

{

    public $num = 0;

    protected static function getInstanceAccessor()

    {

        return A::class;

    }

}

$obj1 = A::getInstance();

$obj1->num++;

var_dump($obj1->num); // 1

$obj2 = A::getInstance();

$obj2->num++;

var_dump($obj2->num); // 2