actor_base.cpp

class Actor {
  std::deque<std::function<void()>> m_messages;

public:
  virtual ~Actor() = default;
  
  void enqueue(std::function<void()> const& func) {
    m_messages.push_back(func);
  }
  
  void process_message() {
    if (m_messages.begin() != m_messages.end()) {
      (*m_messages.begin())();
      m_messages.pop_front();
    }
  }
};