关注点分离 (SoC)

// bad - mixed concernsclass user {    public function save() {        $db = new pdo('mysql:host=localhost;dbname=app', 'user', 'pass');        $stmt = $db->prepare("insert into users (name, email) values (?, ?)");        $stmt->execute([$this->name, $this->email]);    }}// good - separated database logicclass user {    private string $name;    private string $email;}class userrepository {    private pdo $db;    public function save(user $user) {        $stmt = $this->db->prepare("insert into users (name, email) values (?, ?)");        $stmt->execute([$user->getname(), $user->getemail()]);    }}

// bad - mixed validation and business logicclass order {    public function process() {        if (empty($this->items)) {            throw new exception('order cannot be empty');        }        if ($this->total < 0) {            throw new exception('invalid total amount');        }        // process order...    }}// good - separated validationclass ordervalidator {    public function validate(order $order): array {        $errors = [];        if (empty($order->getitems())) {            $errors[] = 'order cannot be empty';        }        if ($order->gettotal() < 0) {            $errors[] = 'invalid total amount';        }        return $errors;    }}class order {    public function process() {        // only handles order processing    }}

// bad - mixed html and logicclass productpage {    public function show($id) {        $product = $this->getproduct($id);        echo "<h1>{$product->name}</h1>";        echo "<p>price: ${$product->price}</p>";    }}// good - separated presentationclass productcontroller {    public function show($id) {        $product = $this->productrepository->find($id);        return $this->view->render('product/show', ['product' => $product]);    }}// product/show.php template<h1><?= htmlspecialchars($product->name) ?></h1><p>price: $<?= htmlspecialchars($product->price) ?></p>

// bad - mixed business logicclass ordercontroller {    public function checkout() {        $order = new order($_post['items']);        $payment = new payment($_post['card']);        $payment->process();        $order->updatestatus('paid');        $email = new emailservice();        $email->sendconfirmation($order);    }}// good - separated servicesclass orderservice {    private paymentservice $paymentservice;    private emailservice $emailservice;    public function processorder(order $order, paymentdata $paymentdata): void {        $this->paymentservice->process($paymentdata);        $order->updatestatus('paid');        $this->emailservice->sendconfirmation($order);    }}class ordercontroller {    public function checkout() {        $this->orderservice->processorder($order, $paymentdata);    }}

// Bad - Hardcoded configurationclass EmailSender {    private $host = 'smtp.example.com';    private $port = 587;    public function send($message) {        // Sending logic using hardcoded values    }}// Good - Separated configuration// config/mail.phpreturn [    'host' => 'smtp.example.com',    'port' => 587];class EmailSender {    private array $config;    public function __construct(array $config) {        $this->config = $config;    }    public function send($message) {        // Sending logic using config values    }}