Explanation of PHP singleton mode (code example)

This article brings you an explanation (code example) about the PHP singleton mode. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

The singleton pattern is a commonly used design pattern and can be seen in many frameworks. The singleton mode can ensure that there is only one instance of a class, thereby facilitating control of the number of instances and saving system resources.

<?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(&#39;Clone is not allowed !&#39;);
    }
}

The singleton pattern may be used multiple times in a system. For easier creation, you can try to establish a general abstraction:

// 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(&#39;Clone is not allowed !&#39;);
    }
}

// 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

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