发布具有不同内容的订阅消息

如何解决发布具有不同内容的订阅消息

嗨，我正在尝试实现pub / sub模式，当消息具有不同的内容类型时，我对实现此模式几乎没有疑问。我的第一种方法（使用单个类型的消息（在这种情况下为字符串））如下：

#pragma once

#include <functional>
#include <list>
#include <memory>
#include <tuple>
#include <unordered_map>

class Broker {

private:
  bool is_running;
  std::unordered_map<TOPIC,std::list<std::function<void(const Message &)>>>
      subscriptions;
  static inline std::shared_ptr<Broker> instance{nullptr};

  Broker() {}

public:
  ~Broker() {}

  static std::shared_ptr<Broker> getInstance() {
    if (instance.get() == nullptr) {
      instance = std::make_shared<Broker>(Broker());
    }
    return instance;
  }

  void subscribe(const TOPIC &topic,const std::function<void(const Message&)> &callback) {
    if (subscriptions.find(topic) == subscriptions.end()) {
      subscriptions.insert({topic,std::list{callback}});
    } else {
      subscriptions[topic].push_back(callback);
    }
  }

  void publish(const Message &message) {
    if (subscriptions.find(message.get_topic()) != subscriptions.end()) {
      for (auto const &call : subscriptions[message.get_topic()]) {
        call(message);
      }
    }
  }
};

// message

#include <string>

enum TOPIC { TOPIC_A,TOPIC_B,TOPIC_C };

class Message {
private:
  TOPIC topic;
  std::string content;

public:
  Message(TOPIC topic,const std::string &content) : topic{topic},content{content} {}
  TOPIC get_topic() const { return this->topic; }
  std::string get_content() const { return this->content; }
};

// in a subscriber
...
broker->subscribe(TOPIC::TOPIC_A,std::bind(...);
broker->subscribe(TOPIC::TOPIC_B,std::bind(...);
...

// in a publisher
....
broker->publish(Message{TOPIC::TOPIC_A,std::string{"some message"});
broker->publish(Message{TOPIC::TOPIC_A,std::string{"other message"});
...

然后我意识到我需要具有不同内容类型的消息，因此我尝试重构代码，这就是我所拥有的：

#pragma once

#include <functional>
#include <list>
#include <memory>
#include <tuple>
#include <unordered_map>

template <class Content>
class Broker {

private:
  bool is_running;
  std::unordered_map<TOPIC,std::list<std::function<void(const Message<Content> &)>>>
      subscriptions;
  static inline std::shared_ptr<Broker> instance{nullptr};

  Broker() {}

public:
  ~Broker() {}

  static std::shared_ptr<Broker> getInstance() {
    if (instance.get() == nullptr) {
      instance = std::make_shared<Broker>(Broker());
    }
    return instance;
  }

  void subscribe(const TOPIC &topic,const std::function<void(const Message<Content> &)> &callback) {
    if (subscriptions.find(topic) == subscriptions.end()) {
      subscriptions.insert({topic,std::list{callback}});
    } else {
      subscriptions[topic].push_back(callback);
    }
  }

  void publish(const Message<Content> &message) {
    if (subscriptions.find(message.get_topic()) != subscriptions.end()) {
      for (auto const &call : subscriptions[message.get_topic()]) {
        call(message);
      }
    }
  }
};

// message
template <class Content> class Message {
private:
  TOPIC topic;
  Content content;

public:
  Message(TOPIC topic,const Content &content) : topic{topic},content{content} {}
  TOPIC get_topic() const { return this->topic; }
  Content get_content() const { return this->content; }
};

// in a subscriber
...
std::shared_ptr<Broker<std::string>> broker =
        Broker<std::string>::getInstance();
broker->subscribe(TOPIC::TOPIC_A,std::bind(...));
std::shared_ptr<Broker<int>> broker1 =
        Broker<int>::getInstance();
broker1->subscribe(TOPIC::TOPIC_B,std::bind(...));
...

因此，现在每次需要具有不同内容类型的消息时，我都必须创建一个不同的Broker。我在打破格局吗？是否有更好（更标准/更有效）的方法来解决此问题？