<?php
interface Subject{
    public function attach(Observer $observer);
    public function detach(Observer $observer);
    public function notify();
}

class SubjectItem implements Subject{
    private $observer_list;
    private $num;

    public function __construct(){
        $this->observer_list = new SplObjectStorage;
    }

    public function attach(Observer $observer){
        $this->observer_list->attach($observer);
    }

    public function detach(Observer $observer){
        $this->observer_list->detach($observer);
    }

    public function setNum($num){
        $this->num = $num;
        $this->notify();
    }

    public function getNum(){
        return $this->num;
    }

    public function notify(){
        for($this->observer_list->rewind();$this->observer_list->valid();$this->observer_list->next()){
            $this->observer_list->current()->update($this);
        }

    }
}

abstract class Observer{
    abstract function update(Subject $subject);
}

class BinObserver extends Observer{
    public function update(Subject $subject){
        echo "二进制更新：".decbin($subject->getNum())."\n";
    }
}

class OctObserver extends Observer{
    public function update(Subject $subject){
        echo "八进制更新：".decoct($subject->getNum())."\n";
    }
}

class HexObserver extends Observer{
    public function update(Subject $subject){
        echo "十六进制更新：".dechex($subject->getNum())."\n";
    }
}

$subject = new SubjectItem();
$subject->attach(new BinObserver());
$subject->attach(new OctObserver());
$subject->attach(new HexObserver());
$subject->setNum(22);

二进制更新：10110
八进制更新：26
十六进制更新：16