PHP 单例模式

<?php

namespace app\comman\auth;
// 单例 一次请求中所有出现都是一个用户
class JwtAuth{
    /**
     * 单例模式
     * @var [type]
     */
    private static $instance;

    private function __construct()
    {
         echo '实例初始化';
    }

    public static function getInstance()
    {
        if (is_null(self::$instance)) {
            self::$instance = new self();
        }
        return self::$instance;
    }


    //阻止用户复制对象实例
    private function __clone()
    {
        trigger_error('禁止克隆' ,E_USER_ERROR);
    }

    function test()
    {
        echo("this is a test");
    }
}

$test = JwtAuth::getInstance();
$test = JwtAuth::getInstance();
$test = JwtAuth::getInstance();
$test = JwtAuth::getInstance();
$test->test();

// 输出结果：实例初始化 this is a test