Just found this snippet of code... it's at least 3 years old. An exception-like event manager for games...

EventManager.hpp

/**
* Template based Event-System by Lukas Kalbertodt <[email protected]>
*/
#pragma once

// needed std headers
#include <map>
#include <memory>
#include <cstring>
#include <set>

/**
* \brief base class for all events
* Has one static method to get a unique id to a event type (nicer than typeid)
* Derived classes should always have a
* typedef MyBase base;
* where "MyBase" is the base class of the derived class.
* Without this typedef the event can not be used with the EventManager!
*/
class Event
{
public:
  template <typename T> static void* GetEventID()
  {
    static int id;
    return static_cast<void*>(&id);
  }
};


/**
* \brief helper traits for lambda function types
* Helper traits to get return type and arg type of a lambda function.
* Uses decltype(&T::operator()) to get types. Works just for one function
* argument, but it is enough for this event system.
* result_type  -> type of the return value
* arg_type     -> type of the argument
*/
template <typename T>
struct lambda_traits
  : public lambda_traits<decltype(&T::operator())>
{};

// specialization for lambdas without parameter (this is an error)
template <typename ClassType, typename ReturnType>
struct lambda_traits<ReturnType(ClassType::*)() const>
{
  static_assert(std::is_void<ClassType>::value,
    "Given lambda function does not have any arguments. It must have const Event& as argument!");
};

// specialization for lambdas we accept
template <typename ClassType, typename ReturnType, typename Arg>
struct lambda_traits<ReturnType(ClassType::*)(Arg) const>
{
  typedef ReturnType result_type;
  typedef Arg arg_type;
};

/**
* \brief Wrapper for different functions
* Wrapper for member functions, normal functions and lambda functions. Is
* sortable, based on
* 1. Size of the function pointer/function object
* 2. Type of the function
* 3. Raw compare of function pointer/function object data
* Attention: Different compilers have different sizes for function pointer/
* function objects. The sort order can differ between different compilers!
*
* Uses type erasure to save different function pointer/objects. Member functions
* do not save the pointer to the object at which it will be called. Object has
* to be passed while calling. This object is ignored when calling a normal
* function or a lambda function.
*/
class EventFunctionWrapper
{
private:
  // Base class for type erasure
  struct FunctionConcept
  {
    FunctionConcept() : m_cmpData(nullptr) {}

    // calling the underlying function on the memberHost (if the underlying
    // function is a member function)
    virtual void operator()(void* memberHost, const Event& event) const = 0;

    // Helper functions for comparing raw data
    virtual void* GetRawData() = 0;
    virtual int GetDataSize() = 0;

    // pointer to data buffer with the comparable data
    char* m_cmpData;
  };

  // class for member functions
  template <typename THost, typename TEvent>
  struct MemberFunctionModel : public FunctionConcept
  {
    // member function pointer
    void(THost::*m_func)(const TEvent&);
    char m_cmpData[sizeof(void(THost::*)(const TEvent&)) + 1];

    MemberFunctionModel(void(THost::*ptr)(const TEvent&)) : m_func(ptr)
    {
      memset(m_cmpData, 0, 1);  // set identifier byte for member function (0)
      memcpy(m_cmpData + 1, &m_func, sizeof(m_func));   // copy member pointer in buffer
    }

    virtual void operator()(void* memberHost, const Event& event) const
    {
      (static_cast<THost*>(memberHost)->*m_func)(static_cast<const TEvent&>(event));
    }

    virtual void* GetRawData()
    {
      return m_cmpData;
    }

    virtual int GetDataSize()
    {
      return sizeof(m_func);
    }
  };

  // class for lambda function
  template <typename TLambda>
  struct LambdaFunctionModel : public FunctionConcept
  {
    // lambda function object of strange type
    TLambda m_func;
    char m_cmpData[sizeof(TLambda) + 1 + sizeof(&TLambda::operator())];

    LambdaFunctionModel(TLambda f) : m_func(f)
    {
      memset(m_cmpData, 1, 1);   // set identifier byte for lambda functions (1)
      memcpy(m_cmpData + 1, &m_func, sizeof(m_func));    // copy lambda data
      auto ptr = &TLambda::operator();
      memcpy(m_cmpData + 1 + sizeof(m_func), &ptr, sizeof(ptr));  // copy function pointer data
    }

    virtual void operator()(void* memberHost, const Event& event) const
    {
      m_func(static_cast<typename lambda_traits<TLambda>::arg_type>(event));
    }

    virtual void* GetRawData()
    {
      return m_cmpData;
    }

    virtual int GetDataSize()
    {
      return sizeof(m_func);
    }
  };

  // class for normal functions
  template <typename TEvent>
  struct RawFunctionModel : public FunctionConcept
  {
    // function pointer
    void(*m_func)(const TEvent&);
    char m_cmpData[sizeof(void(*)(const TEvent&)) + 1];

    RawFunctionModel(void(*ptr)(const TEvent&)) : m_func(ptr)
    {
      memset(m_cmpData, 2, 1);   // set identifier byte for normal function (2)
      memcpy(m_cmpData + 1, &m_func, sizeof(m_func));  // copy function pointer
    }

    virtual void operator()(void* memberHost, const Event& event) const
    {
      m_func(static_cast<const TEvent&>(event));
    }

    virtual void* GetRawData()
    {
      return m_cmpData;
    }

    virtual int GetDataSize()
    {
      return sizeof(m_func);
    }

  };

  // save erased type
  std::shared_ptr<FunctionConcept> m_funcConcept;

public:
  // constructor for member functions
  template <typename THost, typename TEvent>
  EventFunctionWrapper(void(THost::*ptr)(const TEvent&))
    : m_funcConcept(new MemberFunctionModel<THost, TEvent>(ptr))
  {}

  // constructor for lambda functions
  template <typename TLambda>
  EventFunctionWrapper(TLambda ptr)
    : m_funcConcept(new LambdaFunctionModel<TLambda>(ptr))
  {}

  // constructor for normal functions
  template <typename TEvent>
  EventFunctionWrapper(void(*ptr)(const TEvent&))
    : m_funcConcept(new RawFunctionModel<TEvent>(ptr))
  {}

  // calling the underlying function
  void operator()(void* memberHost, const Event& event) const
  {
    (*m_funcConcept)(memberHost, event);
  }

  // compare operator (for more information see above in class description)
  bool operator==(const EventFunctionWrapper& other)
  {
    if(other.m_funcConcept->GetDataSize() != m_funcConcept->GetDataSize())
      return false;
    return (memcmp(other.m_funcConcept->GetRawData(), m_funcConcept->GetRawData(), m_funcConcept->GetDataSize()) == 0);
  }

  // compare operator (for more information see above in class description)
  bool operator<(const EventFunctionWrapper& other) const
  {
    if(other.m_funcConcept->GetDataSize() != m_funcConcept->GetDataSize())
      return m_funcConcept->GetDataSize() < other.m_funcConcept->GetDataSize();
    return (memcmp(other.m_funcConcept->GetRawData(), m_funcConcept->GetRawData(), m_funcConcept->GetDataSize()) > 0);
  }

  // compare operator (for more information see above in class description)
  bool operator>(const EventFunctionWrapper& other) const
  {
    if(other.m_funcConcept->GetDataSize() != m_funcConcept->GetDataSize())
      return m_funcConcept->GetDataSize() > other.m_funcConcept->GetDataSize();
    return (memcmp(other.m_funcConcept->GetRawData(), m_funcConcept->GetRawData(), m_funcConcept->GetDataSize()) < 0);
  }
};


/**
* \brief Manages everything with Events
* Manages Listener to specific event types and calls those Listener when a
* event of that type or a derived type is triggered.
* Works as a singleton!
*/
class EventManager
{
public:
  // typedef for better reading of source code
  typedef void* EventType;
  typedef void* HostType;

  // ---------------------------------------------------------------
  // ------- PUBLIC FUNCTIONS --------------------------------------
  // ---------------------------------------------------------------
  ~EventManager() {}

  /**
  * \brief Returns one instance of EventManager
  */
  static EventManager* GetInstance()
  {
    static EventManager instance;
    return &instance;
  }


  /**
  * \brief Triggers Event and call all Listener
  * When the Event is triggered all Listener on that event are called. Then
  * all Listener on the base event are called (recursive).
  * Note: Never specify the second parameter! You also do not need to specify the template
  * argument, which should be specified with param e.
  * This overloaded function will be called with T!=Event. If T=Event the overloaded method
  * TriggerEvent(T& e, ...) is invoked.
  *
  * \param e The event to trigger. Must be of Type Event or any derived Type.
  */
  template <typename T>
  void TriggerEvent(const T& e)
  {
    // check if T is derived from Event
    static_assert(std::is_base_of<Event, T>::value, "Given Type is not derived from Event!");
    
    // call all functions listening on T
    this->CallAllListener(GetEventID<T>(), e);

    // call all functions listening on base class of T
    this->TriggerEvent(static_cast<const typename T::base&>(e));
  }


  /**
  * \brief Triggers Event and call all Listener
  * When the Event is triggered all Listener on that event are called.
  * Note: Never specify a second parameter! You also do not need to specify the template
  * argument, which should be specified with param e.
  * This overloaded function will be called with T=Event. Every other T will invoke the
  * overloaded function TriggerEvent(T& e, typename T::base* = nullptr).
  *
  * \param e The event to trigger. Must be of Type Event or any derived Type.
  */
  void TriggerEvent(const Event& e)
  {
    // call all functions listening on T
    this->CallAllListener(GetEventID<Event>(), e);
  }


  /**
  * \brief Add a function as listening function to a specific EventType.
  * After registering the function is called when a event of the given type or a derived type is triggered.
  * This method should be used for member functions! For registering other function types see the overloaded
  * methods of RegisterListener below.
  *
  * \param callback pointer to member to the function that should be called if the event is triggered
  * \param obj the object on which the member function should be called
  * \tparam T The type of Event to listen on (must be given as explicit template parameter).
  *      Must be equal to Event or a derived class of Event
  * \tparam F The type of argument, which the member function given with callback accepts.
  *      Implicit given by param callback. F must be T or a baseclass of T!
  */
  template <typename T, typename O, typename F>
  void RegisterListener(void(O::*callback)(const F&), O* obj)
  {
    // check if T is derived from Event or equal to Event
    static_assert(std::is_base_of<Event, T>::value, "Given EventType (Parameter 1) is not derived from Event!");

    // check if the member function fits to T (F must be a baseclass of T or equal to T)
    static_assert(std::is_base_of<F, T>::value, "Given function (Parameter 2) does not accept a Event from type T or any baseclass of T!");

    // wrap pointer to member in our Wrapper and insert it in the set associated with the host and event type
    EventType eID = GetEventID<T>();
    m_Listener[eID][obj].insert(EventFunctionWrapper(callback));
  }

  // RegisterListener for lambda functions (for more information see above)
  template <typename T, typename L>
  void RegisterListener(L lambda, HostType listenerHost = nullptr)
  {
    // check if T is derived from Event or equal to Event
    static_assert(std::is_base_of<Event, T>::value, "Given EventType (Parameter 1) is not derived from Event!");

    // check if lambda function accepts a valid argument
    static_assert(std::is_base_of<typename std::remove_reference<typename lambda_traits<L>::arg_type>::type, T>::value,
      "Given function (Parameter 2) does not accept a Event from type T or any baseclass of T!");

    // wrap lambda in our Wrapper and insert it in the set associated with the event type (host)
    EventType eID = GetEventID<T>();
    m_Listener[eID][listenerHost].insert(EventFunctionWrapper(lambda));
  }

  // RegisterListener for normal functions (for more information see above)
  template <typename T, typename F>
  void RegisterListener(void(*fPtr)(const F&), HostType listenerHost = nullptr)
  {
    // check if T is derived from Event or equal to Event
    static_assert(std::is_base_of<Event, T>::value, "Given EventType (Parameter 1) is not derived from Event!");

    // check if function accepts a valid argument
    static_assert(std::is_base_of<F, T>::value, "Given function (Parameter 2) does not accept a Event from type T or any baseclass of T!");

    // wrap function in our Wrapper and insert it in the set associated with the event type (host)
    EventType eID = GetEventID<T>();
    m_Listener[eID][listenerHost].insert(EventFunctionWrapper(fPtr));
  }



  /**
  * \brief Removes the listener associated with the given event type, function and object
  * This function removes a listener from the intern listener-list. Listener will be
  * deleted, which listen on type T, are associated with the object 'listenerHost' and which
  * function pointer equals the function pointer 'callback'.
  *
  * \param callback pointer to member to a function associated with the listeners to be deleted
  * \param listenerHost the object associated with the listeners to be deleted
  * \tparam T The type of Event associated with the listeners to be deleted
  */
  template <typename T, typename O, typename F>
  void RemoveListener(void(O::*callback)(const F&), O* listenerHost)
  {
    // check if T is derived from Event or equal to Event
    static_assert(std::is_base_of<Event, T>::value, "Given EventType (Parameter 1) is not derived from Event!");

    // check if the member function fits to T (F must be a baseclass of T or equal to T)
    static_assert(std::is_base_of<F, T>::value, "Given function (Parameter 2) does not accept a Event from type T or any baseclass of T!");

    // delete function from set
    EventType eID = GetEventID<T>();
    m_Listener[eID][listenerHost].erase(EventFunctionWrapper(callback));
  }


  /**
  * \brief Removes the listener associated with the given event type and object
  * This function removes a listener from the intern listener-list. Listener will be
  * deleted, which listen on type T and are associated with the object 'obj'
  *
  * \param obj the object associated with the listeners to be deleted
  * \tparam T The type of Event associated with the listeners to be deleted
  */
  template <typename T, typename O>
  void RemoveListener(O* obj)
  {
    EventType eID = GetEventID<T>();
    m_Listener[eID].erase(obj);
  }

  /**
  * \brief Removes the listener associated with the given member function
  *
  * \param callback pointer to member to a function associated with the listeners to be deleted
  * \tparam T The type of Event associated with the listeners to be deleted
  */
  template <typename T, typename O, typename F>
  void RemoveListener(void(O::*callback)(const F&))
  {
    EventType eID = GetEventID<T>();
    for(auto itHosts = m_Listener[eID].begin(); itHosts != m_Listener[eID].end(); itHosts++)
    {
      itHosts->second.erase(EventFunctionWrapper(callback));
    }
  }


  /**
  * \brief Removes the listener associated with the given function and object
  * This function removes a listener from the intern listener-list. Listener will be
  * deleted, which are associated with the object 'obj' and which function pointer
  * equals the function pointer 'callback'. Listener are deleted regardless of event type.
  *
  * \param callback pointer to member to a function associated with the listeners to be deleted
  * \param obj the object associated with the listeners to be deleted
  */
  template <typename O, typename F>
  void RemoveAllListener(void(O::*callback)(const F&), O* listenerHost)
  {
    for(auto itEvents = m_Listener.begin(); itEvents != m_Listener.end(); itEvents++)
    {
      itEvents->second[listenerHost].erase(callback);
    }
  }


  /**
  * \brief Removes the listener associated with the given object
  * This function removes a listener from the intern listener-list. Listener will be
  * deleted, which are associated with the object 'obj', regardless of event type.
  *
  * \param obj the object associated with the listeners to be deleted
  */
  template <typename O>
  void RemoveAllListener(O* obj)
  {
    for(auto it = m_Listener.begin(); it != m_Listener.end(); it++)
    {
      (it->second).erase(obj);
    }
  }

  /**
  * \brief Removes the listener associated with the given member function
  * of all event types
  *
  * \param callback pointer to member to a function associated with the listeners to be deleted
  */
  template <typename O, typename F>
  void RemoveAllListener(void(O::*callback)(const F&))
  {
    for(auto itEvents = m_Listener.begin(); itEvents != m_Listener.end(); itEvents++)
    {
      for(auto itHosts = itEvents->second.begin(); itHosts != itEvents->second.end(); itHosts++)
      {
        itHosts->second.erase(EventFunctionWrapper(callback));
      }
    }
  }


private:
  // ---------------------------------------------------------------
  // ------- PRIVATE FUNCTIONS -------------------------------------
  // ---------------------------------------------------------------
  // private constructor
  EventManager() {}

  /**
  * \brief Calls all listening function to specific EventID
  *
  * \param eID The ID from the EventType
  * \param e The triggered event
  */
  void CallAllListener(EventType eID, const Event& e)
  {
    auto hostMap = m_Listener[eID];
    for(auto itHosts = hostMap.begin(); itHosts != hostMap.end(); itHosts++)
    {
      auto functionSet = itHosts->second;
      for(auto itFunctions = functionSet.begin(); itFunctions != functionSet.end(); itFunctions++)
      {
        (*itFunctions)(itHosts->first, e);
      }
    }
  }

  // small helper to get real event id, independent of references
  template <typename T>
  void* GetEventID()
  {
    return Event::GetEventID<typename std::remove_reference<T>::type>();
  }



  // ---------------------------------------------------------------
  // ------- MEMBER VARIABLEs --------------------------------------
  // ---------------------------------------------------------------
  std::map<EventType, std::map<HostType, std::set<EventFunctionWrapper>>> m_Listener;
};


/**
* \brief Helper to manage event listeners
* Works as base class. The derived class should then register listener
* over the function of this helper class. Then all listener are removed,
* when the destructor of the derived object is called.
*/
template <typename T>
class EventListenerHelper
{
protected:
  EventListenerHelper()
  {
    m_Obj = static_cast<T*>(this);
    m_Mng = EventManager::GetInstance();
  }

  virtual ~EventListenerHelper()
  {
    m_Mng->RemoveAllListener(m_Obj);
  }

  /**
  * \brief Wrapper for EventManager::RegisterListener (see there for further description)
  * notice: There is no wrapper for normal function because it makes no
  * sense to bind normal functions to object
  */
  template <typename E, typename F>
  void RegisterListener(void(T::*callback)(const F&))
  {
    m_Mng->RegisterListener<E>(callback, m_Obj);
  }

  // wrapper for lambda function
  // notice: If the object is deleted, the registered lambda function will
  // be unregistered. If this is not intended use the RegisterListener
  // method directly from EventManager
  template <typename E, typename L>
  void RegisterListener(L lambda)
  {
    m_Mng->RegisterListener<E>(lambda, m_Obj);
  }

private:
  T* m_Obj;
  EventManager* m_Mng;
};