typedef boost::variant< boost::function<void(int)> , boost::function<void(std::string)> > CallbackType ;

void fun2 ( std::string str ) {
    std::cout << " Fun2 : " << str << std::endl ;
}

void init(){
    boost::function<void(std::string)>  f( boost::bind( &CB::fun2, this, _1 ) );
callback_["A"] = f ;
    boost::get< boost::function<void(std::string)> >(callback_["A"])("Ankit");
}

std::map<std::string, CallbackType> callback_ ;