一文探讨常见PHP设计模式之间的区别

class Database
{
   private static $instance;
   private $connection;

   private function __construct()
   {
       $this->connection = new mysqli('localhost', 'user', 'password', 'database');
   } 

   public static function getInstance()
   {
       if (!isset(self::$instance)) {
           self::$instance = new Database();
       }

       return self::$instance;
   }

   public function getConnection()
   {
       return $this->connection;
   }
}

$database = Database::getInstance();
$connection = $database->getConnection();

interface Car
{
   public function run();
}

class BMW implements Car
{
   public function run()
   {
       echo "BMW is running\n";
   }
}

class Benz implements Car
{
   public function run()
   {
       echo "Benz is running\n";
   }
}

interface CarFactory
{
   public function createCar();
}

class BMWFactory implements CarFactory
{
   public function createCar()
   {
       return new BMW();
   }
}

class BenzFactory implements CarFactory
{
   public function createCar()
   {
       return new Benz();
   }
}

$bmwFactory = new BMWFactory();
$bmw = $bmwFactory->createCar();
$bmw->run();

$benzFactory = new BenzFactory();
$benz = $benzFactory->createCar();
$benz->run();

class NewsPublisher implements SplSubject
{
   private $observers = [];
   private $news;

   public function attach(SplObserver $observer)
   {
       $this->observers[] = $observer;
   }

   public function detach(SplObserver $observer)
   {
       $key = array_search($observer, $this->observers, true);
       if ($key !== false) {
           unset($this->observers[$key]);
       }
   }

   public function notify()
   {
       foreach ($this->observers as $observer) {
           $observer->update($this);
       }
   }

   public function publish($news)
   {
       $this->news = $news;
       $this->notify();
   }

   public function getNews()
   {
       return $this->news;
   }
}

class MailSubscriber implements SplObserver
{
   private $email;

   public function __construct($email)
   {
       $this->email = $email;
   }

   public function update(SplSubject $subject)
   {
       echo "Mail sent to ".$this->email." with news: ".$subject->getNews()."\n";
   }
}

$publisher = new NewsPublisher();

$subscriber1 = new MailSubscriber('subscriber1@example.com');
$subscriber2 = new MailSubscriber('subscriber2@example.com');
$subscriber3 = new MailSubscriber('subscriber3@example.com');

$publisher->attach($subscriber1);
$publisher->attach($subscriber2);
$publisher->attach($subscriber3);

$publisher->publish('Breaking news!');

$publisher->detach($subscriber3);

$publisher->publish('Another breaking news!');