How to implement singleton pattern in php

How to implement singleton mode in php: To implement singleton mode, you need to ensure that a class has only one instance and provide a global access point to access it. The singleton pattern does not create a copy of the instance, but returns a reference to the instance stored inside the singleton class.

Definition of singleton pattern:

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Ensure that a class has only one instance and provide a global access point to access it. It does not create a copy of the instance, but returns a reference to the instance stored inside the singleton class.

Three elements of the singleton pattern:

• Requires a static member variable that holds the only instance of the class.

• Constructors and clone functions must be declared private to prevent external programs from creating or making copies of the instance.

• Must provide a public static method to access this instance, thereby returning a reference to the unique instance.

Code implementation:

class Singleton
{
    //创建静态私有的变量保存该类对象
    static private $instance;

    //防止使用new直接创建对象
    private function __construct(){}

    //防止使用clone克隆对象
    private function __clone(){}

    static public function getInstance()
    {
        //判断$instance是否是Singleton的对象，不是则创建
        if (!self::$instance instanceof self) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    public function test()
    {
        echo "我是一个单例模式";
    }
}

$sing = Singleton::getInstance();
$sing->test();
$sing2 = new Singleton(); //Fatal error: Uncaught Error: Call to private Singleton::__construct() from invalid context in
$sing3 = clone $sing; //Fatal error: Uncaught Error: Call to private Singleton::__clone() from context

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