cpp-design-patterns-for-humans/examples/structural/flyweight.cpp

#include <iostream>
#include <memory>
#include <unordered_map>

struct Tea
{
};

class TeaMaker
{
  public:
    std::shared_ptr<Tea> make(const std::string& preference)
    {
      auto match = availableTea_.find(preference);
      if (match == availableTea_.end()) {
        availableTea_[preference] = std::make_shared<Tea>();
      }

      return availableTea_[preference];
    }

    int getPreferenceCount(void)
    {
      return availableTea_.size();
    }

  private:
    std::unordered_map<std::string, std::shared_ptr<Tea>> availableTea_;
};

class TeaShop
{
  public:
    TeaShop(std::shared_ptr<TeaMaker> maker)
        : maker_(maker)
    {
    }

    void takeOrder(const std::string& preference, int table)
    {
      orders_[table] = maker_->make(preference);
    }

    void serve(void)
    {
      for (auto order : orders_) {
        std::cout << "Serving tea to table " << order.first << std::endl;
      }
    }

    int getPreferenceCount(void)
    {
      return maker_->getPreferenceCount();
    }

  private:
    std::shared_ptr<TeaMaker> maker_;
    std::unordered_map<int, std::shared_ptr<Tea>> orders_;
};

int main()
{
  std::shared_ptr<TeaMaker> maker = std::make_shared<TeaMaker>();
  TeaShop shop(maker);

  // No orders have been taken, so there are no available teas.
  std::cout << shop.getPreferenceCount() << std::endl; // Output: 0

  // Take some orders.
  shop.takeOrder("half sugar", 1);
  shop.takeOrder("with milk", 2);
  shop.takeOrder("with boba", 5);

  // We create a new batch of tea for each preference.
  std::cout << shop.getPreferenceCount() << std::endl; // Output: 3

  // Take an order with a previously requested preference.
  shop.takeOrder("half sugar", 4);

  // Since we have some tea from the last time this request was made, no new
  // batch was created.
  std::cout << shop.getPreferenceCount() << std::endl; // Output: 3

  // Serve the customers.
  shop.serve(); 
  // Output: (Note: Since the map is unordered, the serving order may vary.)
  // Serving tea to table 4
  // Serving tea to table 5
  // Serving tea to table 1
  // Serving tea to table 2

  return 0;
}