The SplObserver interface

<?php/** * Subject,that who makes news */class Newspaper implements \SplSubject{    private $name;    private $observers = array();    private $content;        public function __construct($name) {        $this->name = $name;    }    //add observer    public function attach(\SplObserver $observer) {        $this->observers[] = $observer;    }        //remove observer    public function detach(\SplObserver $observer) {                $key = array_search($observer,$this->observers, true);        if($key){            unset($this->observers[$key]);        }    }        //set breakouts news    public function breakOutNews($content) {        $this->content = $content;        $this->notify();    }        public function getContent() {        return $this->content." ({$this->name})";    }        //notify observers(or some of them)    public function notify() {        foreach ($this->observers as $value) {            $value->update($this);        }    }}/** * Observer,that who recieves news */class Reader implements SplObserver{    private $name;        public function __construct($name) {        $this->name = $name;    }        public function update(\SplSubject $subject) {        echo $this->name.' is reading breakout news <b>'.$subject->getContent().'</b><br>';    }}$newspaper = new Newspaper('Newyork Times');$allen = new Reader('Allen');$jim = new Reader('Jim');$linda = new Reader('Linda');//add reader$newspaper->attach($allen);$newspaper->attach($jim);$newspaper->attach($linda);//remove reader$newspaper->detach($linda);//set break outs$newspaper->breakOutNews('USA break down!');//=====output======//Allen is reading breakout news USA break down! (Newyork Times)//Jim is reading breakout news USA break down! (Newyork Times)

Beware, you have written :        if($key){            unset($this->observers[$key]);        }When this should be :        if(false !== $key){            unset($this->observers[$key]);        }If the observer you want to delete is the first in your array, you will never delete it because the key would equal 0 and 0 == false as you know.