function_message_bus.hpp

#include <string>
#include <map>
#include <functional>
#include <cassert>
#include "function_traits.hpp"
#include "type_name.hpp"

    template <typename... Args, typename Func, std::size_t... Idx>
    void for_each(const std::tuple<Args...>& t, Func&& f, std::index_sequence<Idx...>) {
        (void)std::initializer_list<int> { (f(std::get<Idx>(t)), void(), 0)...};
    }
    
struct FnKey {
        std::string key;
    };

    class FunctionMsgBus {
    public:
        static FunctionMsgBus& get()
        {
            static FunctionMsgBus instance;
            return instance;
        }

        template<typename Function, typename=std::enable_if_t<!std::is_member_function_pointer<Function>::value>>
        void register_handler(const Function& f, std::string const & additional="")
        {
            using namespace std::placeholders;
            auto key = get_key<Function>(additional);
            check_duplicate(key);

            invokers_[key] = { std::bind(&invoker<Function>::apply, f, _1, _2) };
        }

        template <typename Function, typename Self, typename = std::enable_if_t<std::is_member_function_pointer<Function>::value>>
        void register_handler(Function f, Self* t, std::string const & additional ="") {
            using namespace std::placeholders;
            auto key = get_key<Function>(additional);
            check_duplicate(key);

            invokers_[key] = { std::bind(&invoker<Function>::template apply_mem<Self>, f, t, _1, _2) };
        }

        //non-void function
        template <typename T, typename U, typename ... Args>
        T call(U&& u, Args&& ... args)
        {
            std::string key = get_key(std::forward<U>(u), std::forward<Args>(args)...);
            auto it = invokers_.find(key);
            assert(it != invokers_.end());

            T t;
            call_impl(it, &t, std::forward<U>(u), std::forward<Args>(args)...);
            return t;
        }

        //void function
        template <typename U, typename ... Args>
        void call(U&& u, Args&& ... args)
        {
            std::string key = get_key(std::forward<U>(u), std::forward<Args>(args)...);
            auto it = invokers_.find(key);
            assert(it != invokers_.end());

            call_impl(it, nullptr, std::forward<U>(u), std::forward<Args>(args)...);
        }

    private:
        FunctionMsgBus() {};
        FunctionMsgBus(const FunctionMsgBus&) = delete;
        FunctionMsgBus(FunctionMsgBus&&) = delete;

        template <typename T, typename U, typename ... Args>
        void call_impl(T it, void* ptr, U&& u, Args&& ... args){
            auto args_tuple = get_args_tuple(std::integral_constant<bool, std::is_same<U, FnKey>::value>{},
                                             std::forward<U>(u), std::forward<Args>(args)...);
            using Tuple = decltype(args_tuple);
            using storage_type = typename std::aligned_storage<sizeof(Tuple), alignof(Tuple)>::type;
            storage_type data;
            Tuple* tp = new (&data) Tuple;
            *tp = args_tuple;

            it->second(tp, ptr);
        }

        void check_duplicate(const std::string& key){
            auto it = invokers_.find(key);
            if(it!=invokers_.end())
                assert("duplicate register");
        }

        template<typename Function>
        std::string get_key(std::string const & additional) {
            if(!additional.empty())
                return additional;

            using tuple_type = typename function_traits<Function>::bare_tuple_type;
            auto key = get_name_from_tuple(tuple_type{});
            return key;
        }

        template <typename U, typename ... Args>
        std::enable_if_t<std::is_same<U, FnKey>::value, std::string> get_key(U&& u, Args&& ... args) {
            return u.key;
        }

        template <typename U, typename ... Args>
        std::enable_if_t<!std::is_same<U, FnKey>::value, std::string> get_key(U&& u, Args&& ... args) {
            return get_name(std::forward<U>(u), std::forward<Args>(args)...);
        }

        template <typename U, typename ... Args>
        auto get_args_tuple(std::true_type, U&& u, Args&& ... args)-> decltype(std::make_tuple(std::forward<Args>(args)...)) {
            return std::make_tuple(std::forward<Args>(args)...);
        }

        template <typename U, typename ... Args>
        auto get_args_tuple(std::false_type, U&& u, Args&& ... args) ->decltype(std::make_tuple(std::forward<U>(u), std::forward<Args>(args)...)){
            return std::make_tuple(std::forward<U>(u), std::forward<Args>(args)...);
        }

        template<typename... Args>
        std::string get_name(Args&&... args) {
            std::string name = "";
            std::initializer_list<int>{(name += type_name<Args>(), 0)...};
            return name;
        }

        struct caller{
            caller(std::string& name):name_(name){

            }
            template<typename T>
            void operator()(const T& t){
                name_+= type_name<T>();
            }

            std::string& name(){
                return name_;
            }

            std::string& name_;
        };

        template<typename T>
        std::string get_name_from_tuple(T t) {
            std::string name = "";

            for_each(t, caller{name}, std::make_index_sequence<std::tuple_size<T>::value>{});
            return name;
        }

        template<typename Function>
        struct invoker
        {
            static inline void apply(const Function& func, void* bl, void* result)
            {
                using tuple_type = typename function_traits<Function>::bare_tuple_type;
                const tuple_type* tp = static_cast<tuple_type*>(bl);
                call(func, *tp, result);
            }

            template<typename F, typename ... Args>
            static typename std::enable_if<std::is_void<typename std::result_of<F(Args...)>::type>::value>::type
            call(const F& f, const std::tuple<Args...>& tp, void*)
            {
                call_helper(f, std::make_index_sequence<sizeof... (Args)>{}, tp);
            }

            template<typename F, typename ... Args>
            static typename std::enable_if<!std::is_void<typename std::result_of<F(Args...)>::type>::value>::type
            call(const F& f, const std::tuple<Args...>& tp, void* result)
            {
                auto r = call_helper(f, std::make_index_sequence<sizeof... (Args)>{}, tp);
                if(result)
                *(decltype(r)*)result = r;
            }

            template<typename F, size_t... I, typename ... Args>
            static auto call_helper(const F& f, const std::index_sequence<I...>&, const std::tuple<Args...>& tup)-> typename std::result_of<F(Args...)>::type
            {
                return f(std::get<I>(tup)...);
            }

            template <typename Self>
            static inline void apply_mem(Function f, Self* self, void* bl, void* result)
            {
                using tuple_type = typename function_traits<Function>::bare_tuple_type;
                const tuple_type* tp = static_cast<tuple_type*>(bl);

                using return_type = typename function_traits<Function>::return_type;
                call_mem(f, self, *tp, result, std::integral_constant<bool, std::is_void<return_type>::value>{});
            }

            template<typename F, typename Self, typename ... Args>
            static void call_mem(F f, Self* self, const std::tuple<Args...>& tp, void*, std::true_type)
            {
                call_member_helper(f, self, std::make_index_sequence<sizeof...(Args)>{}, tp);
            }

            template<typename F, typename Self, typename ... Args>
            static void call_mem(F f, Self* self, const std::tuple<Args...>& tp, void* result, std::false_type)
            {
                auto r = call_member_helper(f, self, std::make_index_sequence<sizeof...(Args)>{}, tp);
                if(result)
                *(decltype(r)*)result = r;
            }

            template<typename F, typename Self, size_t... I, typename ... Args>
            static auto call_member_helper(F f, Self* self, const std::index_sequence<I...>&, const std::tuple<Args...>& tup)-> decltype((self->*f)(std::get<I>(tup)...))
            {
                return (self->*f)(std::get<I>(tup)...);
            }
        };

        private:
        std::map<std::string, std::function<void(void*, void*)>> invokers_;
    };