Advanced Design Patterns in PHP: Code Examples

Design Patterns in PHP: Advanced Level

Design patterns are proven solutions to typical problems that arise in software development. At the beginner level, developers learn Singleton, Factory, or Adapter. However, in complex, high-load, or flexible systems in PHP, more powerful and abstract patterns are required. In this article, we will cover four advanced patterns with real code examples in PHP: Strategy, Factory Method, Observer, and State.

1. Strategy Pattern

Purpose: Defines a family of algorithms, encapsulates each one, and makes them interchangeable. Allows changing the behavior of an object at runtime without modifying its code.

Example: A payment processing system. We have several payment methods: credit card, PayPal, cryptocurrency. Each method has its own validation and processing logic.

<?php\n\n// Strategy interface\ninterface PaymentStrategy\n{\n    public function pay(float $amount): void;\n    public function validate(): bool;\n}\n\n// Concrete strategies\nclass CreditCardPayment implements PaymentStrategy\n{\n    private string $cardNumber;\n    private string $cvv;\n\n    public function __construct(string $cardNumber, string $cvv)\n    {\n        $this->cardNumber = $cardNumber;\n        $this->cvv = $cvv;\n    }\n\n    public function validate(): bool\n    {\n        // Simple check of card number length\n        return strlen($this->cardNumber) === 16 && strlen($this->cvv) === 3;\n    }\n\n    public function pay(float $amount): void\n    {\n        if (!$this->validate()) {\n            throw new \\InvalidArgumentException("Invalid card data");\n        }\n        echo "Paid {$amount} via credit card {$this->cardNumber}.<br>";\n    }\n}\n\nclass PayPalPayment implements PaymentStrategy\n{\n    private string $email;\n\n    public function __construct(string $email)\n    {\n        $this->email = $email;\n    }\n\n    public function validate(): bool\n    {\n        return filter_var($this->email, FILTER_VALIDATE_EMAIL) !== false;\n    }\n\n    public function pay(float $amount): void\n    {\n        if (!$this->validate()) {\n            throw new \\InvalidArgumentException("Invalid PayPal email");\n        }\n        echo "Paid {$amount} via PayPal ({$this->email}).<br>";\n    }\n}\n\n// Context (client)\nclass OrderProcessor\n{\n    private PaymentStrategy $strategy;\n\n    public function setPaymentStrategy(PaymentStrategy $strategy): void\n    {\n        $this->strategy = $strategy;\n    }\n\n    public function processOrder(float $total): void\n    {\n        if (!isset($this->strategy)) {\n            throw new \\RuntimeException("Payment method not selected");\n        }\n        $this->strategy->pay($total);\n    }\n}\n\n// Usage\n$order = new OrderProcessor();\n$order->setPaymentStrategy(new CreditCardPayment('1234567812345678', '123'));\n$order->processOrder(150.00);\n// Output: Paid 150 via credit card 1234567812345678.\n\n?>

Advantages: Easily add new algorithms (new payment methods) without modifying existing code. The code becomes flexible and testable.

2. Factory Method Pattern

Purpose: Defines an interface for creating an object but allows subclasses to alter the type of object that will be created. This is the base pattern for all creational patterns.

Example: Generating different types of reports (PDF, HTML, JSON) depending on user request.

<?php\n\n// Abstract product\ninterface Report\n{\n    public function generate(): string;\n}\n\n// Concrete products\nclass PdfReport implements Report\n