Is it possible to create a variadic template function with a few parameters being non-variadic?

Question

So i am trying to make class Bed inherit from class Device. I know the constructor is called with an int, Socket class and Ini class; the thing i dont know is whether or not more arguments are passed of different classes.

thats what im trying to do here in my Bed.cpp file:

#include "Bed.h"
#include <fstream>
#include <string>
#include <sstream>
#include <iostream>
#include <unistd.h>
#include <string>
#include <vector>
#include "Socket.h"
#include "Ini.h"

using namespace std;

class Socket;
class Ini;

template <typename... Types> Bed<Types...>::Bed(int number, Socket s, Ini i, const Types&... var): id(number), socket(s), ini(i) {
    if (typeid(var).name() == "Button") {
        buttons_.push_back(var);
    } else if (typeid(var).name() == "Led") {
        leds_.push_back(var);
    } else if (typeid(var).name() == "RGBled") {
        rgbleds_.push_back(var);
    } else {
        cout<<"error"<<endl;
    }
}

template <typename... Types> void Bed<Types...>::check() {
    for (int i = 0; i <= buttons_.size() - 1; i++) {
        buttons_[i].getStatus();
    }
    getPressure();
}

template <typename... Types> void Bed<Types...>::getPressure() {

}

this is my Bed.h file:

#ifndef BED_H_
#define BED_H_

#include <string>
#include <vector>
#include <iostream>
#include <cstdarg>

using namespace std;

class Device;
class Socket;
class Ini;

template <typename... Types> class Bed: public Device {
public:
    Bed(int, Socket, Ini, const Types...);
    void getPressure();
    void check();
private:
    int pressureSensor = 0;
};

#endif

and this is my Device.h file:

#ifndef DEVICE_H_
#define DEVICE_H_

#include <string>
#include <vector>
#include <iostream>
#include <cstdarg>

using namespace std;

class Button;
class Led;
class RGBled;
class Socket;
class Ini;

template <typename... Types> class Device {
public:
    //Device(int, Socket, Ini, const Types&...);
    virtual void check();
    //virtual ~Device();
private:
    vector<Led> leds_;
    vector<Button> buttons_;
    vector<RGBled> rgbleds_;
    Socket socket;
    Ini ini;
    int id;
};

#endif

In my Bed.cpp, I get the error

declaration is incompatible with "Bed::Bed(int, Socket, Ini, Types...)" (declared at line 17 of "/home/programmer/project/Bed.h")

which is the line

Bed(int, Socket, Ini, const Types...);

I've been trying to fix this for hours now, and at this point I've got no clue anymore.

Answer 1

One way of getting at this problem would be to let your Device have an add_component function that can add a Led/Button/RGBLed to the vectors. You could then forward your type-pack to that function.

template <typename... Types> class Device {
public:
    //Device(int, Socket, Ini, const Types&...);
    virtual void check();
    //virtual ~Device();
    void add_component(Led led); { leds_.push_back(led); }
    void add_component(Button button); { buttons_.push_back(button); }
    void add_component(RGBled rgbled); { rgbleds_.push_back(rgbled); }
private:
    vector<Led> leds_;
    vector<Button> buttons_;
    vector<RGBled> rgbleds_;
    Socket socket;
    Ini ini;
    int id;
};

template <typename... Types> Bed<Types...>::Bed(int number, Socket s, Ini i, const 
Types&... var): id(number), socket(s), ini(i) {
    (add_component(var), ...);
}

(add_component(var), ...); is a folding expression and will unfold to

(add_component(var1), add_component(var2), ..., add_component(varN));

Overload resultion in the three add_component methods will take care of adding the component to the right vector.

Since it don't know what these types are, the components are passed by value here. A sensible default if the thing is very cheap to copy. Inconsistent with the constructor that takes the arguments by cont-ref, but sorting the details of that out is left as an exercise to the reader.