EventEmitter.cpp

//
// Copyright (c) 2014 Sean Farrell
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy 
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights 
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
// copies of the Software, and to permit persons to whom the Software is 
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in 
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
// SOFTWARE.
//

#include "EventEmitter.h"

#include <stdexcept>

EventEmitter::EventEmitter() {}

EventEmitter::~EventEmitter() {}

unsigned int EventEmitter::add_listener(unsigned int event_id, std::function<void ()> cb)
{
    if (!cb)
    {
        throw std::invalid_argument("EventEmitter::add_listener: No callbak provided.");
    }
    
    std::lock_guard<std::mutex> lock(mutex);

    unsigned int listener_id = ++last_listener;
    listeners.insert(std::make_pair(event_id, std::make_shared<Listener<>>(listener_id, cb)));

    return listener_id;       
}

unsigned int EventEmitter::on(unsigned int event_id, std::function<void ()> cb)
{
    return add_listener(event_id, cb);
}

void EventEmitter::remove_listener(unsigned int listener_id)
{
    std::lock_guard<std::mutex> lock(mutex);

    auto i = std::find_if(listeners.begin(), listeners.end(), [&] (std::pair<const unsigned int, std::shared_ptr<ListenerBase>> p) {
        return p.second->id == listener_id;
    });
    if (i != listeners.end())
    {
        listeners.erase(i);
    }
    else
    {
        throw std::invalid_argument("EventEmitter::remove_listener: Invalid listener id.");
    }
}

EventEmitter.h

//
// Copyright (c) 2014 Sean Farrell
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy 
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights 
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
// copies of the Software, and to permit persons to whom the Software is 
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in 
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
// SOFTWARE.
//

#ifndef _EVENT_EMITTER_H_
#define _EVENT_EMITTER_H_

#include <functional>
#include <map>
#include <memory>
#include <mutex>
#include <list>
#include <algorithm>

class EventEmitter
{
public:
    
    EventEmitter();

    ~EventEmitter();

    template <typename... Args>
    unsigned int add_listener(unsigned int event_id, std::function<void (Args...)> cb);

    unsigned int add_listener(unsigned int event_id, std::function<void ()> cb);

    template<typename LambdaType>
    unsigned int add_listener(unsigned int event_id, LambdaType lambda) {
        return add_listener(event_id, make_function(lambda));
    }

    template <typename... Args>
    unsigned int on(unsigned int event_id, std::function<void (Args...)> cb);
    
    unsigned int on(unsigned int event_id, std::function<void ()> cb);

    template<typename LambdaType>
    unsigned int on(unsigned int event_id, LambdaType lambda) {
        return on(event_id, make_function(lambda));
    }

    void remove_listener(unsigned int listener_id);

    template <typename... Args>
    void emit(unsigned int event_id, Args... args);

private:
    struct ListenerBase
    {
        ListenerBase() {}

        ListenerBase(unsigned int i)
        : id(i) {}

        virtual ~ListenerBase() {}

        unsigned int id;
    };

    template <typename... Args>
    struct Listener : public ListenerBase
    {
        Listener() {}

        Listener(unsigned int i, std::function<void (Args...)> c)
        : ListenerBase(i), cb(c) {}

        std::function<void (Args...)> cb;
    };

    std::mutex mutex;
    unsigned int last_listener;
    std::multimap<unsigned int, std::shared_ptr<ListenerBase>> listeners;

    EventEmitter(const EventEmitter&) = delete;  
    const EventEmitter& operator = (const EventEmitter&) = delete;



    // http://stackoverflow.com/a/21000981
    template <typename T>
    struct function_traits
       : public function_traits<decltype(&T::operator())>
    {};

    template <typename ClassType, typename ReturnType, typename... Args>
    struct function_traits<ReturnType(ClassType::*)(Args...) const> {
       typedef std::function<ReturnType (Args...)> f_type;
    };

    template <typename L> 
    typename function_traits<L>::f_type make_function(L l){
      return (typename function_traits<L>::f_type)(l);
    }
};

template <typename... Args>
unsigned int EventEmitter::add_listener(unsigned int event_id, std::function<void (Args...)> cb)
{
    if (!cb)
    {
        throw std::invalid_argument("EventEmitter::add_listener: No callbak provided.");
    }

    std::lock_guard<std::mutex> lock(mutex);

    unsigned int listener_id = ++last_listener;
    listeners.insert(std::make_pair(event_id, std::make_shared<Listener<Args...>>(listener_id, cb)));

    return listener_id;        
}

template <typename... Args>
unsigned int EventEmitter::on(unsigned int event_id, std::function<void (Args...)> cb)
{
    return add_listener(event_id, cb);
}

template <typename... Args>
void EventEmitter::emit(unsigned int event_id, Args... args)
{
    std::list<std::shared_ptr<Listener<Args...>>> handlers;
    
    {
        std::lock_guard<std::mutex> lock(mutex);

        auto range = listeners.equal_range(event_id);
        handlers.resize(std::distance(range.first, range.second));
        std::transform(range.first, range.second, handlers.begin(), [] (std::pair<const unsigned int, std::shared_ptr<ListenerBase>> p) {
            auto l = std::dynamic_pointer_cast<Listener<Args...>>(p.second);
            if (l)
            {
                return l;
            }
            else
            {
                throw std::logic_error("EventEmitter::emit: Invalid event signature.");
            }
        });
    }

    for (auto& h : handlers)
    {
        h->cb(args...);
    }        
}

#endif

test.cpp

#include "EventEmitter.h"
#include <iostream>
#include <functional>

using namespace std;

void print(const char* str) {
    cout << str << endl;
}

class Baz {
public:
    void act(const char* action) {
        cout << "Baz doing " << action << endl;
    }
};

int main() {
    EventEmitter emitter;

    // Using lambda:
    emitter.on(0, [](int foo, double bar) { 
        cout << "foo: " << foo << endl;
        cout << "bar: " << bar << endl;
    });
    emitter.emit(0, 2, 3.7);

    // Using std::function
    emitter.on(1, std::function<void(const char*)>(print));
    emitter.emit(1, "Hello World!");

    // Using std::bind
    Baz baz;
    std::function<void(const char*)> action = std::bind(&Baz::act, &baz, std::placeholders::_1);
    emitter.on(2, action);
    emitter.emit(2, "something awesome");

    return 0;
}

How about a lambda function?

class Data: public EventEmitter{
public:
    void activate(){
        this->on(1, [this] (auto message) {
            this->show(message);
        }
    }
    
    void show(const char* message){
        cout << message << endl;        
    }
};

Also you probably want to use enums as event identifiers. See the associated blog post: http://www.rioki.org/2014/12/29/eventemitter-in-c.html