PHP 設計パターン: 保守性のベスト プラクティス

class Singleton
{
    private static $instance = null;

    public static function getInstance(): Singleton
    {
        if (self::$instance === null) {
            self::$instance = new Singleton();
        }

        return self::$instance;
    }
}

// 使用单例模式
$instance1 = Singleton::getInstance();
$instance2 = Singleton::getInstance();

// 验证是否是同个实例
var_dump($instance1 === $instance2); // true

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

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

class User implements Subject
{
    private $observers = [];

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

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

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

class Logger implements Observer
{
    public function update(Subject $subject)
    {
        // 记录用户状态更改
        echo "User状态已更改为：" . $subject->getState() . PHP_EOL;
    }
}

// 使用观察者模式
$user = new User();
$logger = new Logger();
$user->attach($logger);

// 用户状态更改
$user->setState("已登录");

// 记录用户状态更改
$user->notify();

interface DatabaseConnectionFactory
{
    public function createConnection(): DatabaseConnection;
}

class MySQLConnectionFactory implements DatabaseConnectionFactory
{
    public function createConnection(): DatabaseConnection
    {
        return new MySQLConnection();
    }
}

class PostgreSQLConnectionFactory implements DatabaseConnectionFactory
{
    public function createConnection(): DatabaseConnection
    {
        return new PostgreSQLConnection();
    }
}

// 使用工厂方法模式
$factory = new MySQLConnectionFactory();
$connection = $factory->createConnection();

// 现在您可以使用 $connection 对象连接到数据库

interface SortStrategy
{
    public function sort(array $data);
}

class BubbleSortStrategy implements SortStrategy
{
    public function sort(array $data)
    {
        // 实现插入排序算法
    }
}

class QuickSortStrategy implements SortStrategy
{
    public function sort(array $data)
    {
        // 实现快速排序算法
    }
}

// 使用战略模式
$data = [1, 5, 2, 3, 4];
$strategy = new QuickSortStrategy();
$sortedData = $strategy->sort($data);

// 现在 $sortedData 中包含已排序的数据