Following is a basic instance of what I am doing in my C++ program. I have a list of listeners which are all std::functions. I have a concept DataType which means what kind of data the listener is interested in. The idea here is the same as publish-subscribe pattern. A method interested in certain kind of data should be able to add itself to the list of listeners using AddListener. Some methods are added & they receive a callback whenever required.
The program works fine !!
#include <iostream>
#include <functional>
#include <vector>
#include <string>
enum class DataType {
Type_1,
Type_2
// and so on
};
typedef std::function<void(std::pair<DataType, std::string>)> MyListenerType;
//template <typename T>
//typedef std::function<void(T>)> MyListenerType;
// How can I emulate the above so that a method passing any kind of primitive data-type namely "int, bool, float or double" can be added into
// my vector of listners.
std::vector<MyListenerType> my_data_listeners_1;
std::vector<MyListenerType> my_data_listeners_2;
void ListenerMethod_Instance_1(std::pair<DataType, std::string> information) {
DataType data_type = information.first;
std::string message = information.second;
std::cout << "ListenerMethod_Instance_1 called with message " << message << "\n";
}
void ListenerMethod_Instance_2(std::pair<DataType, std::string> information) {
DataType data_type = information.first;
std::string message = information.second;
std::cout << "ListenerMethod_Instance_2 called with message " << message << "\n";
}
void AddListener (MyListenerType listener, DataType type_of_interest) {
if (DataType::Type_1 == type_of_interest) {
my_data_listeners_1.push_back(listener);
std::cout << "Added a method instance for DataType::Type_1" << "\n";
}
else if (DataType::Type_2 == type_of_interest) {
my_data_listeners_2.push_back(listener);
std::cout << "Added a method instance for DataType::Type_2" << "\n";
}
else {
std::cout << "Listener type not supported" << "\n";
}
}
void CallAllListnersWhohaveSuscribed() {
if (!my_data_listeners_1.empty()) {
std::string send_message_1 = "some message 123";
std::pair <DataType, std::string> info_to_send_1 = std::make_pair (DataType::Type_1, send_message_1);
for(auto const &listener : my_data_listeners_1) {
listener(info_to_send_1);
}
}
if (!my_data_listeners_2.empty()) {
std::string send_message_2 = "some message 456";
std::pair <DataType, std::string> info_to_send_2 = std::make_pair (DataType::Type_2, send_message_2);
for(auto const &listener : my_data_listeners_2) {
listener(info_to_send_2);
}
}
}
int main() {
// Add ListenerMethod_Instance_1 for instance
DataType data_type_1 = DataType::Type_1;
auto listener_instance_1 = std::bind(ListenerMethod_Instance_1, std::placeholders::_1);
AddListener(listener_instance_1, data_type_1);
// Add ListenerMethod_Instance_2 for instance
DataType data_type_2 = DataType::Type_2;
auto listener_instance_2 = std::bind(ListenerMethod_Instance_2, std::placeholders::_1);
AddListener(listener_instance_2, data_type_2);
CallAllListnersWhohaveSuscribed();
return 0;
}
Following is the output of the program:
./stdFunctionTest
Added a method instance for DataType::Type_1
Added a method instance for DataType::Type_2
ListenerMethod_Instance_1 called with message some message 123
ListenerMethod_Instance_2 called with message some message 456
But here is how I want to modify & struggling with. The caveat is that every ListenerMethod_Instance_1 & ListenerMethod_Instance_2 have to parse the pair to get their info which I don't want to. I want to enable a method of any C++ primitive data type be it "int, bool, float or double" to be able to be added into the listeners vector & receive the callback. For example following method should be "add-able" into AddListener. Looking at this link here looks some
void ListenerMethod_Instance_3(int integer_data) {
std::cout << "ListenerMethod_Instance_3 called with integer_data " << integer_data << "\n";
}
So, basically how can I achieve templates functionality with std::functions ?
Aucun commentaire:
Enregistrer un commentaire