CODESAMPLE

Strategy - PHP

Strategy PHP

The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It allows an algorithm to vary independently from the clients that use it. This implementation uses an interface PaymentStrategy to define a common method for making payments. Concrete strategies like CreditCardPayment and PayPalPayment implement this interface with specific payment logic. A ShoppingCart class accepts a PaymentStrategy via dependency injection and uses it to process the payment, without needing to know the specifics of how the payment is made. This fits PHP’s flexible type system and encourages loose coupling through interfaces.

<?php

/**
 * Payment Strategy Interface
 */
interface PaymentStrategy
{
    public function pay(float $amount): bool;
}

/**
 * Concrete Strategy: Credit Card Payment
 */
class CreditCardPayment implements PaymentStrategy
{
    private string $cardNumber;
    private string $cvv;

    public function __construct(string $cardNumber, string $cvv)
    {
        $this->cardNumber = $cardNumber;
        $this->cvv = $cvv;
    }

    public function pay(float $amount): bool
    {
        // Simulate credit card processing
        echo "Paid $amount using Credit Card ($this->cardNumber)\n";
        return true;
    }
}

/**
 * Concrete Strategy: PayPal Payment
 */
class PayPalPayment implements PaymentStrategy
{
    private string $email;

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

    public function pay(float $amount): bool
    {
        // Simulate PayPal processing
        echo "Paid $amount using PayPal ($this->email)\n";
        return true;
    }
}

/**
 * Context: Shopping Cart
 */
class ShoppingCart
{
    private PaymentStrategy $paymentStrategy;

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

    public function setPaymentStrategy(PaymentStrategy $paymentStrategy): void
    {
        $this->paymentStrategy = $paymentStrategy;
    }

    public function checkout(float $amount): bool
    {
        return $this->paymentStrategy->pay($amount);
    }
}

// Usage
$cart = new ShoppingCart(new CreditCardPayment("1234-5678-9012-3456", "123"));
$cart->checkout(100.00);

$cart->setPaymentStrategy(new PayPalPayment("user@example.com"));
$cart->checkout(50.00);

?>