PHP类实例化与方法调用策略：静态方法与依赖注入

class EmailService
{
    private EntityManagerInterface $entityManager;
    private EmailFactory $emailFactory;

    public function __construct(EntityManagerInterface $em, EmailFactory $emailFactory)
    {
        $this->entityManager = $em;
        $this->emailFactory = $emailFactory;
    }

    public function sendPaymentEmail(string $sender, User $user, string $template): bool
    {
        // 实际发送邮件的逻辑，会用到 $this->entityManager 和 $this->emailFactory
        echo "Sending payment email from {$sender} to {$user->getEmail()} using template {$template}\n";
        return true;
    }
}

class PaymentService
{
    // ... 其他属性和方法

    public function sendPaymentEmail(User $user)
    {
        // 错误：Too few arguments to function App\Service\EmailService::__construct(), 0 passed
        $emailService = new EmailService(); 
        $sender = 'no-reply@example.com'; // 假设这里获取发件人

        return $emailService->sendPaymentEmail($sender, $user, 'customer_home');
    }
}

class EmailService
{
    // 如果方法是静态的，则通常不应依赖实例属性，
    // 因此，__construct 和私有属性可能不再需要，或者需要重新设计。
    // 为了演示，我们假设sendPaymentEmail被简化为不需要这些依赖。
    // 如果静态方法确实需要这些依赖，它们必须作为参数传入。

    public static function sendPaymentEmail(string $sender, User $user, string $template): bool
    {
        // 假设这里直接处理邮件发送，不依赖EntityManagerInterface或EmailFactory
        // 或者这些依赖作为额外参数传入
        echo "Sending payment email from {$sender} to {$user->getEmail()} using template {$template} via static method\n";
        return true;
    }
}

class PaymentService
{
    // ... 其他属性和方法

    public function sendPaymentEmail(User $user)
    {
        $sender = 'no-reply@example.com'; 
        // 直接通过类名调用静态方法
        return EmailService::sendPaymentEmail($sender, $user, 'customer_home');
    }
}

class PaymentService
{
    private EmailService $emailService;

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

    public function sendPaymentEmail(User $user)
    {
        $sender = 'no-reply@example.com'; 
        // 使用注入的 EmailService 实例
        return $this->emailService->sendPaymentEmail($sender, $user, 'customer_home');
    }
}

// 假设在一个入口文件或服务容器配置中
// 首先，容器会创建 EmailService 的依赖
$entityManager = /* 获取 EntityManagerInterface 实例 */;
$emailFactory = /* 获取 EmailFactory 实例 */;

// 然后，容器创建 EmailService 实例
$emailService = new EmailService($entityManager, $emailFactory);

// 最后，容器创建 PaymentService 实例，并注入 EmailService
$paymentService = new PaymentService($emailService);

// 现在可以调用 PaymentService 的方法
$user = new User('test@example.com'); // 假设 User 类存在
$paymentService->sendPaymentEmail($user);

class PaymentService
{
    // 假设 PaymentService 可能有其他核心依赖，但 EmailService 不是
    // ...

    public function sendPaymentEmail(User $user, EmailService $emailService) // EmailService 作为参数
    {
        $sender = 'no-reply@example.com'; 
        // 使用通过方法参数注入的 EmailService 实例
        return $emailService->sendPaymentEmail($sender, $user, 'customer_home');
    }
}

// 同样，通常由容器或更高层级的代码负责创建 EmailService 实例
$entityManager = /* 获取 EntityManagerInterface 实例 */;
$emailFactory = /* 获取 EmailFactory 实例 */;
$emailService = new EmailService($entityManager, $emailFactory);

$paymentService = new PaymentService(); // 如果 PaymentService 构造器没有其他依赖
$user = new User('test@example.com');

// 调用方法时传入 EmailService 实例
$paymentService->sendPaymentEmail($user, $emailService);