CODESAMPLE

Proxy - C++

Proxy C++

The Proxy pattern provides a surrogate or placeholder for another object to control access to it. This is useful for scenarios like remote access, security checks, or lazy initialization. The Subject interface defines the common access point, the RealSubject is the actual object of interaction, and the Proxy controls access to the RealSubject.

This C++ implementation uses smart pointers (std::shared_ptr) to manage the lifetime of the RealSubject within the Proxy. The Proxy intercepts requests and performs actions (like logging or access control) before forwarding them to the RealSubject. Using interfaces (std::enable_shared_from_this) allows the RealSubject to be safely shared through the Proxy. This approach is idiomatic C++ due to its emphasis on resource management and the use of RAII principles.

#include <iostream>
#include <memory>
#include <string>

// Forward declaration
class RealSubject;

// Subject interface
class Subject {
public:
    virtual ~Subject() = default;
    virtual void request() = 0;
};

// RealSubject
class RealSubject : public std::enable_shared_from_this<RealSubject> {
public:
    void request() {
        std::cout << "RealSubject: Handling request." << std::endl;
    }
};

// Proxy
class Proxy : public Subject {
public:
    Proxy(std::shared_ptr<RealSubject> realSubject) : realSubject_(realSubject) {}

    void request() override {
        std::cout << "Proxy: Logging the request before forwarding." << std::endl;
        // Add access control or other logic here if needed
        if (realSubject_) {
            realSubject_->request();
        } else {
            std::cout << "Proxy: RealSubject is unavailable." << std::endl;
        }
    }

private:
    std::shared_ptr<RealSubject> realSubject_;
};

// Client code
int main() {
    auto realSubject = std::make_shared<RealSubject>();
    auto proxy = std::make_shared<Proxy>(realSubject);

    proxy->request();

    // Simulate RealSubject becoming unavailable
    realSubject.reset();
    proxy->request();

    return 0;
}