proxy.cpp

// Proxy design pattern

#include <iostream>
#include <memory>

// car interface
struct ICar {
    virtual void drive() const = 0;
    virtual ~ICar() = default;
};

// concrete car
class Car : public ICar {
    void drive() const override { std::cout << "Driving a car!\n"; }
};

// proxy to a car, additional checks
class Car_Proxy : public ICar {
    std::unique_ptr<ICar> car_{std::make_unique<Car>()};
    unsigned age_;

  public:
    Car_Proxy(unsigned age) : age_{age} {}
    void drive() const override {
        if (age_ < 18) {
            std::cout << "You cannot drive a car yet!\n";
        } else {
            car_->drive();
        }
    }
};

int main() {
    Car_Proxy underage_driver(17);
    underage_driver.drive();

    Car_Proxy driver(18);
    driver.drive();
}