C++ 继承示例

#include <algorithm>
#include <atomic>
#include <cassert>
#include <iostream>
#include <map>
#include <mutex>
#include <vector>

class Container {
 public:
  Container() {
      std::lock_guard<std::mutex> lock(mut);
      auto it = uuid.load();
      uuid.store(++it);
      serial_number_ = it;
      container_map.insert({ serial_number_, this });
  }

  virtual int get_fluid_capacity() = 0;

  friend int totalFluidCapacity() {
    std::lock_guard<std::mutex> lock(mut);
    int result = 0;
    for (auto& it : container_map) {
      result += it.second->get_fluid_capacity();
    }
    return result;
  }

  friend Container* find_container(size_t serial_number) {
    std::lock_guard<std::mutex> lock(mut);
    if(container_map.find(serial_number) != container_map.end()) {
      return container_map[serial_number];
    } else {
      return nullptr;
    }
  }
  inline static std::mutex mut;
  inline static std::atomic<size_t> uuid;
  inline static std::map<size_t, Container*> container_map;

 protected:
  size_t serial_number_;
};

int totalFluidCapacity();
Container* find_container(size_t serial_number);

class Buckets : public Container {
  static constexpr double pi = 3.1415926;

 public:
  Buckets(int height, int radius) : height_(height), radius_(radius) {}
  virtual int get_fluid_capacity() override final {
    return static_cast<int>(radius_ * radius_ * height_ * pi);
  }

 private:
  int height_;
  int radius_;
};

class Boxes : public Container {
 public:
  enum class material_type : int {
    m = 0,  /// for metal
    c = 1,  /// for cardboard
  };

  Boxes(const int length, const int width, const int height, material_type type)
      : length_(length), width_(width), height_(height), type_(type) {}
  virtual int get_fluid_capacity() override final {
    if (type_ == material_type::c) {
      return length_ * width_ * height_;
    } else {
      return 0;
    }
  }

 private:
  int length_;
  int width_;
  int height_;
  material_type type_;
};

int main() {
  Boxes box_c(1, 1, 1, Boxes::material_type::c);
  Boxes box_m(1, 1, 1, Boxes::material_type::m);

  Buckets bucket(1, 1);

  auto capa = totalFluidCapacity();
  assert(capa == 4);

  auto p_container = find_container(2);
  assert(p_container == & box_m);
  return 0;
}