实现PHP内部的通知机制，如当一个类的属性发生变化时，另外一个类就可以收到通知设计模式：观察者模式使用场景参考链接

<?php
abstract class EventGenerator
{
    public $observers = [];
    public function addObservers(Observer $observer)
    {
        $this->observers[] = $observer;
    }
    public function notify($info = '')
    {
        foreach ($this->observers as $observer) {
            $observer->getInfo($info);
        }
    }
}

interface Observer
{
    function getInfo($info = '');
}

class Observer1 implements Observer
{
    
    public function getInfo($info = '')
    {
        echo $info;
    }
}

class Events extends EventGenerator
{
    private $info = 'init';

    public function trigger($info = '')
    {
        echo "before:".$this->info."\r\n";
        $this->info = $info;
        echo "after:".$this->info."\r\n";
        $this->notify($info);
    }
}

$event = new Events();
$event->addObservers(new Observer1());
$event->trigger('hello world');