PHP设计模式：与行为型编程的关系

interface Observer {
    public function update($subject);
}

class ConcreteObserver1 implements Observer {
    public function update($subject) {
        echo "ConcreteObserver1 received update from $subject\n";
    }
}

class ConcreteObserver2 implements Observer {
    public function update($subject) {
        echo "ConcreteObserver2 received update from $subject\n";
    }
}

class Subject {
    private $observers = [];

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

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

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

// 实战案例
$subject = new Subject();
$observer1 = new ConcreteObserver1();
$observer2 = new ConcreteObserver2();
$subject->attach($observer1);
$subject->attach($observer2);
$subject->notify(); // 输出："ConcreteObserver1 received update from Subject" 和 "ConcreteObserver2 received update from Subject"

interface Strategy {
    public function doOperation($a, $b);
}

class ConcreteStrategyA implements Strategy {
    public function doOperation($a, $b) {
        return $a + $b;
    }
}

class ConcreteStrategyB implements Strategy {
    public function doOperation($a, $b) {
        return $a - $b;
    }
}

class Context {
    private $strategy;

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

    public function doOperation($a, $b) {
        return $this->strategy->doOperation($a, $b);
    }
}

// 实战案例
$context = new Context(new ConcreteStrategyA());
echo $context->doOperation(10, 5); // 输出：15

$context = new Context(new ConcreteStrategyB());
echo $context->doOperation(10, 5); // 输出：5

interface Command {
    public function execute();
}

class ConcreteCommand implements Command {
    private $receiver;

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

    public function execute() {
        $this->receiver->action();
    }
}

class Receiver {
    public function action() {
        echo "Receiver action executed\n";
    }
}

class Invoker {
    private $commands = [];

    public function setCommand(Command $command) {
        $this->commands[] = $command;
    }

    public function invoke() {
        foreach ($this->commands as $command) {
            $command->execute();
        }
    }
}

// 实战案例
$receiver = new Receiver();
$command = new ConcreteCommand($receiver);
$invoker = new Invoker();
$invoker->setCommand($command);
$invoker->invoke(); // 输出："Receiver action executed"